water

Water
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This article is about general aspects of water. For a detailed discussion of its properties, see water (properties). For other uses, see Water (disambiguation).
Water in three states: liquid, solid (ice), and (invisible) water vapor in the air. Clouds are the accumulations of the droplets, condensed from vapor-saturated air.

Water is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.[1]

In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface[2]. On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation.[3] Oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within biological bodies and manufactured products.

Water moves continually through a cycle of evaporation or transpiration (evapotranspiration), precipitation, and runoff, usually reaching the sea. Over land, evaporation and transpiration contribute to the precipitation over land.

Clean, fresh drinking water is essential to human and other lifeforms. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world.[4][5] There is a clear correlation between access to safe water and GDP per capita.[6] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[7] Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70 percent of freshwater is consumed by agriculture.[8]
Contents
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* 1 Chemical and physical properties
* 2 Taste and odor
* 3 Distribution of water in nature
o 3.1 Water in the universe
o 3.2 Water and habitable zone
* 4 Water on Earth
o 4.1 Water cycle
o 4.2 Fresh water storage
o 4.3 Sea water
o 4.4 Tides
* 5 Effects on life
o 5.1 Aquatic life forms
* 6 Effects on human civilization
o 6.1 Health and pollution
o 6.2 Human uses
+ 6.2.1 Agriculture
+ 6.2.2 Water as a scientific standard
+ 6.2.3 For drinking
+ 6.2.4 Hygiene
+ 6.2.5 Chemical uses
+ 6.2.6 As a heat transfer fluid
+ 6.2.7 Extinguishing fires
+ 6.2.8 Recreation
+ 6.2.9 Water industry
+ 6.2.10 Industrial applications
+ 6.2.11 Food processing
* 7 Water politics and water crisis
* 8 Water in culture
o 8.1 Religion
o 8.2 Philosophy
o 8.3 Literature
* 9 See also
o 9.1 Other topics
* 10 References
* 11 Further reading
o 11.1 Water as a natural resource
* 12 External links

Chemical and physical properties
Main articles: Water (properties), Water (data page), and Water model
Model of hydrogen bonds between molecules of water
Impact from a water drop causes an upward "rebound" jet surrounded by circular capillary waves.
Snowflakes by Wilson Bentley, 1902
Dew drops adhering to a spider web
Capillary action of water compared to mercury

Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.

Water appears in nature in all three common states of matter and may take many different forms on Earth: water vapor and clouds in the sky; seawater and icebergs in the polar oceans; glaciers and rivers in the mountains; and the liquid in aquifers in the ground.

The major chemical and physical properties of water are:

* Water is a tasteless, odorless liquid at standard temperature and pressure. The color of water and ice is, intrinsically, a very light blue hue, although water appears colorless in small quantities. Ice also appears colorless, and water vapor is essentially invisible as a gas.[9]

* Water is transparent, and thus aquatic plants can live within the water because sunlight can reach them. Only strong UV light is slightly absorbed.

* Since the water molecule is not linear and the oxygen atom has a higher electronegativity than hydrogen atoms, it carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar molecule with an electrical dipole moment. The net interactions between the dipoles on each molecule cause an effective skin effect at the interface of water with other substances, or air at the surface, the latter given rise to water's high surface tension. This dipolar nature contributes to water molecules' tendency to form hydrogen bonds which cause water's many special properties.[10] The polar nature also favors adhesion to other materials.

* A result of interplay of these properties, Capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.

* Water is a good solvent and is often referred to as the universal solvent. Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases – especially oxygen, carbon dioxide (carbonation) are known as hydrophilic (water-loving) substances, while those that do not mix well with water (e.g., fats and oils), are known as hydrophobic (water-fearing) substances.

* All the major components in cells (proteins, DNA and polysaccharides) are also dissolved in water.

* Pure water has a low electrical conductivity, but this increases significantly with the dissolution of a small amount of ionic material such as sodium chloride.

* The boiling point of water (and all other liquids) is dependent on the barometric pressure. For example, on the top of Mt. Everest water boils at about 68 °C (154 °F), compared to 100 °C (212 °F) at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.

* Water has the second highest specific heat capacity of any known substance, after ammonia, as well as a high heat of vaporization (40.65 kJ·mol−1), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.

* The maximum density of water occurs at 3.98 °C (39.16 °F).[11] Water becomes even less dense upon freezing, expanding 9%. This results in an unusual phenomenon: water's solid form, ice, floats upon water, allowing organisms to survive inside a partially-frozen water body because the water on the bottom has a temperature of around 4 °C (39 °F).

ADR label for transporting goods dangerously reactive with water

* Water is miscible with many liquids, for example ethanol, in all proportions, forming a single homogeneous liquid. On the other hand, water and most oils are immiscible usually forming layers according to increasing density from the top. As a gas, water vapor is completely miscible with air.

* Water forms an azeotrope with many other solvents.

* Water can be split by electrolysis into hydrogen and oxygen.

* As an oxide of hydrogen, water is formed when hydrogen or hydrogen-containing compounds burn or react with oxygen or oxygen-containing compounds. Water is not a fuel, it is an end-product of the combustion of hydrogen. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy released when the hydrogen and oxygen recombine.[12]

* Elements which are more electropositive than hydrogen such as lithium, sodium, calcium, potassium and caesium displace hydrogen from water, forming hydroxides. Being a flammable gas, the hydrogen given off is dangerous and the reaction of water with the more electropositive of these elements may be violently explosive.

* At ultrahigh pressures found in deep interiors of giant planets Uranus and Neptune water may become metallic, which would have important implications for the generation of the magnetic fields of these planets.[citation needed]

Taste and odor

Water can dissolve many different substances, giving it varying tastes and odors. Humans and other animals have developed senses which (more or less) enable them to evaluate the potability of water by avoiding water that is too salty or putrid. Humans also tend to prefer cold water to lukewarm water since cold water is likely to contain fewer microbes. The taste advertised in spring water or mineral water derives from the minerals dissolved in it: Pure H2O is tasteless and odorless. The advertised purity of spring and mineral water refers to absence of toxins, pollutants and microbes.
Distribution of water in nature
Water in the universe

Much of the universe's water may be produced as a byproduct of star formation. When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.[13]

Water has been detected in interstellar clouds within our galaxy, the Milky Way. Water probably exists in abundance in other galaxies, too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Interstellar clouds eventually condense into solar nebulae and solar systems such as ours.

Water vapor is present on:

* Mercury - 3.4% in the atmosphere, and large amounts of water in Mercury's exosphere[14]
* Venus - 0.002% in the atmosphere
* Earth - trace in the atmosphere (varies with climate)
* Mars - 0.03% in the atmosphere
* Jupiter - 0.0004% in the atmosphere
* Saturn - in ices only
* Enceladus (moon of Saturn) - 91% in the atmosphere
* exoplanets known as HD 189733 b[15] and HD 209458 b.[16]

Liquid water is present on:

* Earth - 71% of surface
* Moon - small amounts of water have been found (in 2008) in the inside of volcanic pearls brought from Moon to Earth by the Apollo 15 crew in 1971.[17] NASA reported the detection of water molecules by NASA's Moon Mineralogy Mapper aboard the Indian Space Research Organization's Chandrayaan-1 spacecraft in September 2009.[18]

Strong evidence suggests that liquid water is present just under the surface of Saturn's moon Enceladus and on Jupiter's moon Europa.

Water ice is present on:

* Earth - mainly as ice sheets
* polar ice caps on Mars
* Titan
* Europa
* Enceladus
* Comets and comet source populations (Kuiper belt and Oort cloud objects).

Water ice may be present on the Moon, Ceres, and Tethys. Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune.
Water and habitable zone
The Solar System along center row range of possible habitable zones of varying size stars.

The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the solar system; if it were slightly closer to or further from the Sun (about 5%, or about 8 million kilometres), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.[19][20]

Earth's gravity allows it to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in polar ice caps (as on Mars).

The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity.

There are various theories about origin of water on Earth.
Water on Earth
Main articles: Hydrology and Water distribution on Earth
Water covers 71% of the Earth's surface; the oceans contain 97.2% of the Earth's water. The Antarctic ice sheet, which contains 90% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as clouds, contributing to the Earth's albedo.

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in focus of ecohydrology.

The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1,360,000,000 km3 (326,000,000 mi3). Of this volume:[citation needed]
A graphical distribution of the locations of water on Earth.

* 1,320,000,000 km3 (316,900,000 mi3 or 97.2%) is in the oceans.
* 25,000,000 km3 (6,000,000 mi3 or 1.8%) is in glaciers, ice caps and ice sheets.
* 13,000,000 km3 (3,000,000 mi3 or 0.9%) is groundwater.
* 250,000 km3 (60,000 mi3 or 0.02%) is fresh water in lakes, inland seas, and rivers.
* 13,000 km3 (3,100 mi3 or 0.001%) is atmospheric water vapor at any given time.

Groundwater and fresh water are useful or potentially useful to humans as water resources.

Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.

Water is important in many geological processes. Groundwater is ubiquitous in rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes at subduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes. Water and, to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic record of Earth history.
Water cycle
Main article: Water cycle
Water cycle

The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.

Water moves perpetually through each of these regions in the water cycle consisting of following transfer processes:

* evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into air.
* precipitation, from water vapor condensing from the air and falling to earth or ocean.
* runoff from the land usually reaching the sea.

Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year. Precipitation, at a rate of 107 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew. Condensed water in the air may also refract sunlight to produce rainbows.

Water runoff often collects over watersheds flowing into rivers. A mathematical model used to simulate river or stream flow and calculate water quality parameters is hydrological transport model. Some of water is diverted to irrigation for agriculture. Rivers and seas offer opportunity for travel and commerce. Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water. It is when a river overflows its banks or flood from the sea. A drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation.
Fresh water storage
Bay of Fundy High Tide.jpgBay of Fundy Low Tide.jpg
High tide (left) and low tide (right).
Main article: Water resources

Some runoff water is trapped for periods of time, for example in lakes. At high altitude, during winter, and in the far north and south, snow collects in ice caps, snow pack and glaciers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. This water storage is important, since clean, fresh water is essential to human and other land-based life. In many parts of the world, it is in short supply.
Sea water
Main article: Seawater

Sea water contains about 3.5% salt on average, plus smaller amounts of other substances. The physical properties of sea water differ from fresh water in some important respects. It freezes at a lower temperature (about -1.9C) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing. The salinity of water in major seas varies from about 0.7% in the Baltic Sea to 4.0% in the Red Sea.
Tides
Main article: Tide

Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.
Effects on life
An oasis is an isolated water source with vegetation in desert
Overview of photosynthesis and respiration. Water (at right), together with carbon dioxide (CO2), form oxygen and organic compounds (at left), which can be respired to water and (CO2).

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g. starches, triglycerides and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g. glucose, fatty acids and amino acids to be used for fuels for energy use or other purposes). Water is thus essential and central to these metabolic processes. Therefore, without water, these metabolic processes would cease to exist, leaving us to muse about what processes would be in its place, such as gas absorption, dust collection, etc.

Water is also central to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as hydroxide ion (OH−) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7.
Some of the biodiversity of a coral reef

Stomach acid (HCl) is useful to digestion. However, its corrosive effect on the esophagus during reflux can temporarily be neutralized by ingestion of a base such as aluminum hydroxide to produce the neutral molecules water and the salt aluminum chloride. Human biochemistry that involves enzymes usually performs optimally around a biologically neutral pH of 7.4.

For example a cell of Escherichia coli contains 70% of water, a human body 60–70%, plant body up to 90% and the body of an adult jellyfish is made up of 94–98% water.
Aquatic life forms
Main articles: Hydrobiology and Aquatic plant
Some marine diatoms - a key phytoplankton group

Earth's waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales that also live in the water. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.

Aquatic animals must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Smaller life forms are able to absorb oxygen through their skin.
Effects on human civilization
Water Fountain

Civilization has historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.
Health and pollution
Environmental Science Program, Iowa State University student sampling water.

Water fit for human consumption is called drinking water or potable water. Water that is not potable can be made potable by filtration or distillation (heating it until it becomes water vapor, and then capturing the vapor without any of the impurities it leaves behind), or by other methods (chemical or heat treatment that kills bacteria). Sometimes the term safe water is applied to potable water of a lower quality threshold (i.e., it is used effectively for nutrition in humans that have weak access to water cleaning processes, and does more good than harm). Water that is not fit for drinking but is not harmful for humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water).

This natural resource is becoming scarcer in certain places, and its availability is a major social and economic concern. Currently, about a billion people around the world routinely drink unhealthy water. Most countries accepted the goal of halving by 2015 the number of people worldwide who do not have access to safe water and sanitation during the 2003 G8 Evian summit.[21] Even if this difficult goal is met, it will still leave more than an estimated half a billion people without access to safe drinking water and over a billion without access to adequate sanitation. Poor water quality and bad sanitation are deadly; some five million deaths a year are caused by polluted drinking water. The World Health Organization estimates that safe water could prevent 1.4 million child deaths from diarrhea each year.[22] Water, however, is not a finite resource, but rather re-circulated as potable water in precipitation in quantities many degrees of magnitude higher than human consumption. Therefore, it is the relatively small quantity of water in reserve in the earth (about 1 percent of our drinking water supply, which is replenished in aquifers around every 1 to 10 years), that is a non-renewable resource, and it is, rather, the distribution of potable and irrigation water which is scarce, rather than the actual amount of it that exists on the earth. Water-poor countries use importation of goods as the primary method of importing water (to leave enough for local human consumption), since the manufacturing process uses around 10 to 100 times products' masses in water.

In the developing world, 90% of all wastewater still goes untreated into local rivers and streams.[23] Some 50 countries, with roughly a third of the world’s population, also suffer from medium or high water stress, and 17 of these extract more water annually than is recharged through their natural water cycles.[24] The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
Human uses
Agriculture
Irrigation of field crops

The most important use of water in agriculture is for irrigation, which is a key component to produce enough food. Irrigation takes up to 90% of water withdrawn in some developing countries[25] and significant proportions in developed countries (United States, 30% of freshwater usage is for irrigation).[26]
Water as a scientific standard

On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one hundredth of a metre, and to the temperature of the melting ice."[27] For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).[28]

The Kelvin temperature scale of the SI system is based on the triple point of water, defined as exactly 273.16 K or 0.01 °C. The scale is a more accurate development of the Celsius temperature scale, which was originally defined according the boiling point (set to 100 °C) and melting point (set to 0 °C) of water.

Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also small quantity of heavier isotopes such as hydrogen-2 (deuterium). The amount of deuterium oxides or heavy water is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less deuterium than seawater. Therefore, standard water is defined in the Vienna Standard Mean Ocean Water specification.
For drinking
Main article: Drinking water
A young girl drinking bottled water

The human body is anywhere from 55% to 78% water depending on body size.[29] To function properly, the body requires between one and seven litres of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though most advocates agree that 6–7 glasses of water (approximately 2 litres) daily is the minimum to maintain proper hydration.[30] Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.[31] For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source.[32] There are other myths such as the effect of water on weight loss and constipation that have been dispelled.[33]
Hazard symbol for No drinking water

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."[34] The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.[35] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicine—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—this is recommended to be 2.4 litres (10 cups) for pregnant women and 3 litres (12 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.[36] Also noted is that normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water that does not contain too many impurities. Common impurities include metal salts and oxides (including copper, iron, calcium and lead)[37] and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.[38]

The single largest freshwater resource suitable for drinking is Lake Baikal in Siberia, which has a very low salt and calcium content and is therefore very clean.
Hygiene

The ability of water to make solutions and emulsions is used for washing. Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances.
Chemical uses

Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.
As a heat transfer fluid
Ice used for cooling.

Water and steam are used as heat transfer fluids in diverse heat exchange systems, due to its availability and high heat capacity, both as a coolant and for heating. Cool water may even be naturally available from a lake or the sea. Condensing steam is a particularly efficient heating fluid because of the large heat of vaporization. A disadvantage is that water and steam are somewhat corrosive. In almost all electric power stations, water is the coolant, which vaporizes and drives steam turbines to drive generators. In the U.S., cooling power plants is the largest use of water.[26]

In the nuclear industry, water can also be used as a neutron moderator. In a pressurized water reactor, water is both a coolant and a moderator. This provides a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down.
Extinguishing fires
Water is used for fighting wildfires.

Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. However, water cannot be used to fight fires of electric equipment, because impure water is electrically conductive, or of oils and organic solvents, because they float on water and the explosive boiling of water tends to spread the burning liquid.

Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot graphite, decompose the water, producing hydrogen gas.

The power of such explosions was seen in the Chernobyl disaster, although the water involved did not come from fire-fighting at that time but the reactor's own water cooling system. A steam explosion occurred when the extreme over-heating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of reaction between steam and hot zirconium.
Recreation
Main article: Water sport (recreation)

Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice. Lakesides, beaches and waterparks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other water features in public or private decorations.. Some keep fish and other life in aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports i.e. skiing, sledding, snowmobiling or snowboarding, which requires the water to be frozen. People may also use water for play fighting such as with snowballs, water guns or water balloons.
Water industry
A water-carrier in India, 1882. In many places where running water is not available, water has to be transported by people.
A manual water pump in China
Water purification facility
Main articles: Water industry and :Category:Water supply and sanitation by country

The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities includes for example water wells cisterns for rainwater harvesting, water supply network, water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development.

Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid climates.

The distribution of drinking water is done through municipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource and to finance the boring of wells or the construction of dams and reservoirs.

Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources.

Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market cannot account. Thus other people pay the price of water pollution, while the private firms' profits are not redistributed to the local population victim of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

Wastewater facilities are storm sewers and wastewater treatment plants. Another way to remove pollution from surface runoff water is bioswale.
Industrial applications

Water is used in power generation. Hydroelectricity is electricity obtained from hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the sun. Heat from the sun evaporates water, which condenses as rain in higher altitudes, from where it flows down.
Three Gorges Dam is the largest hydro-electric power station

Pressurized water is used in water blasting and water jet cutters. Also, very high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent over-heating, or prevent saw blades from over-heating.

Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge.
Food processing
Water can be used to cook foods such as noodles.

Water plays many critical roles within the field of food science. It is important for a food scientist to understand the roles that water plays within food processing to ensure the success of their products.

Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water is affected by solutes. One mole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C, and one mole of salt per kg raises the boiling point by 1.02 °C; similarly, increasing the number of dissolved particles lowers water's freezing point.[39] Solutes in water also affect water activity which affects many chemical reactions and the growth of microbes in food.[40] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.[39] Solutes in water lower water activity. This is important to know because most bacterial growth ceases at low levels of water activity.[40] Not only does microbial growth affect the safety of food but also the preservation and shelf life of food.

Water hardness is also a critical factor in food processing. It can dramatically affect the quality of a product as well as playing a role in sanitation. Water hardness is classified based on the amounts of removable calcium carbonate salt it contains per gallon. Water hardness is measured in grains; 0.064 g calcium carbonate is equivalent to one grain of hardness.[39] Water is classified as soft if it contains 1 to 4 grains, medium if it contains 5 to 10 grains and hard if it contains 11 to 20 grains.[vague] [39] The hardness of water may be altered or treated by using a chemical ion exchange system. The hardness of water also affects its pH balance which plays a critical role in food processing. For example, hard water prevents successful production of clear beverages. Water hardness also affects sanitation; with increasing hardness, there is a loss of effectiveness for its use as a sanitizer.[39]

Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam, While cooking water is used for dishwashing too.
Water politics and water crisis
Best estimate of the share of people in developing countries with access to drinking water 1970–2000.
Main articles: Water politics and Water crisis
See also: Water resources, Water law, and Water right

Water politics is politics affected by water and water resources. For this reason, water is a strategic resource in the globe and an important element in many political conflicts. It causes health impacts and damage to biodiversity.

1.6 billion people have gained access to a safe water source since 1990 [1]. The proportion of people in developing countries with access to safe water is calculated to have improved from 30 percent in 1970[4] to 71 percent in 1990, 79 percent in 2000 and 84 percent in 2004. This trend is projected to continue.[5] To halve, by 2015, the proportion of people without sustainable access to safe drinking water is one of the Millennium Development Goals. This goal is projected to be reached.

A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption.[41]

UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30 percent. 40 percent of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from waterborne diseases (related to the consumption of contaminated water) or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases; often this means lack of sewage disposal; see toilet.

Organizations concerned in water protection include International Water Association (IWA), WaterAid, Water 1st, American Water Resources Association. Water related conventions are United Nations Convention to Combat Desertification (UNCCD), International Convention for the Prevention of Pollution from Ships, United Nations Convention on the Law of the Sea and Ramsar Convention. World Day for Water takes place on 22 March and World Ocean Day on 8 June.

Water used in the production of a good or service is virtual water.
Water in culture
Religion
A Hindu ablution as practiced in Tamil Nadu

Water is considered a purifier in most religions. Major faiths that incorporate ritual washing (ablution) include Christianity, Hinduism, Rastafarianism, Islam, Shinto, Taoism, and Judaism. Immersion (or aspersion or affusion) of a person in water is a central sacrament of Christianity (where it is called baptism); it is also a part of the practice of other religions, including Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the five daily prayers can be done in most cases (see Tayammum) after completing washing certain parts of the body using clean water (wudu). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of misogi). Water is mentioned in the Bible 442 times in the New International Version and 363 times in the King James Version: 2 Peter 3:5(b) states, "The earth was formed out of water and by water" (NIV).

Some faiths use water especially prepared for religious purposes (holy water in some Christian denominations, Amrita in Sikhism and Hinduism). Many religions also consider particular sources or bodies of water to be sacred or at least auspicious; examples include Lourdes in Roman Catholicism, the Jordan River (at least symbolically) in some Christian churches, the Zamzam Well in Islam and the River Ganges (among many others) in Hinduism.

Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganges is also personified as a goddess, while Saraswati have been referred to as goddess in Vedas. Also water is one of the "panch-tatva"s (basic 5 elements, others including fire, earth, space, air). Alternatively, gods can be patrons of particular springs, rivers, or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids.
Philosophy

The Ancient Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic substance of the universe. Water was considered cold and moist. In the theory of the four bodily humors, water was associated with phlegm. The classical element of Water was also one of the five elements in traditional Chinese philosophy, along with earth, fire, wood, and metal.

Water is also taken as a role model in some parts of traditional and popular Asian philosophy. James Legge's 1891 translation of the Dao De Jing states "The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the Tao" and "There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it;--for there is nothing (so effectual) for which it can be changed."[42]
Literature

Water is used in literature as a symbol of purification. Examples include the critical importance of a river in As I Lay Dying by William Faulkner and the drowning of Ophelia in Hamlet.
See also
Water portal
Main article: Outline of water

* The Outline of water is a collection of links to Wikipedia articles which discuss water's importance in chemistry, physics, electronics, geography, geology, meteorology, biology, agriculture, medicine, geology, hydrology, paleontology, politics, society, and culture.
* The Water (data page) is a collection of the chemical and physical properties of water.

Water is described in many terms and contexts:

* according to state
o solid - ice
o liquid - water
o gaseous - water vapor

* according to meteorology:
o hydrometeor
+ precipitation

precipitation according to movement precipitation according to state


* vertical (falling) precipitation
o rain
o freezing rain
o drizzle
o freezing drizzle
o snow
o snow pellets
o snow grains
o ice pellets
o frozen rain
o hail
o ice crystals
* horizontal (seated) precipitation
o dew
o hoarfrost
o atmospheric icing
o glaze ice



* liquid precipitation
o rain
o freezing rain
o drizzle
o freezing drizzle
o dew
* solid precipitation
o snow
o snow pellets
o snow grains
o ice pellets
o frozen rain
o hail
o ice crystals
o hoarfrost
o atmospheric icing
o glaze ice
* mixed precipitation
o in temperatures around 0 °C

*
o levitating particles
+ clouds
+ fog
+ mist
o ascending particles (drifted by wind)
+ spindrift
+ stirred snow
* according to occurrence
o groundwater
o meltwater
o meteoric water
o connate water
o fresh water
o surface water
o mineral water – contains many minerals
o brackish water
o dead water – strange phenomenon which can occur when a layer of fresh or brackish water rests on top of denser salt water, without the two layers mixing. It is dangerous for ship traveling.
o seawater
o brine
* according to uses
o tap water
o bottled water
o drinking water or potable water – useful for everyday drinking, without fouling, it contains balanced minerals that are not harmful to health (see below)
o purified water, laboratory-grade, analytical-grade or reagent-grade water – water which has been highly purified for specific uses in science or engineering. Often broadly classified as Type I, Type II, or Type III, this category of water includes, but is not limited to the following:
+ distilled water
+ double distilled water
+ deionized water

* according to other features
o soft water – contains less minerals
o hard water – from underground, contains more minerals
o distilled water, double distilled water, deionized water - contains no minerals
o Water of crystallization — water incorporated into crystalline structures
o Hydrates — water bound into other chemical substances
o heavy water – made from heavy atoms of hydrogen - deuterium. It is in nature in normal water in very low concentration. It was used in construction of first nuclear reactors.
o tritiated water

* according to microbiology
o drinking water
o wastewater
o stormwater or surface water

* according to religion
o holy water

Other topics
Sustainable development portal

* Dihydrogen monoxide hoax
* Water Pasteurization Indicator
* Water intoxication

References

1. ^ United Nations
2. ^ "CIA- The world fact book". Central Intelligence Agency. https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html#Geo. Retrieved 2008-12-20.
3. ^ Water Vapor in the Climate System, Special Report, [AGU], December 1995 (linked 4/2007). Vital Water UNEP.
4. ^ a b Björn Lomborg (2001). The Skeptical Environmentalist. Cambridge University Press. p. 22. ISBN 0521010683. http://www.lomborg.com/dyn/files/basic_items/69-file/skeptenvironChap1.pdf.
5. ^ a b MDG Report 2008
6. ^ "Public Services", Gapminder video
7. ^ Kulshreshtha, S.N (1998). "A Global Outlook for Water Resources to the Year 2025". Water Resources Management 12 (3): 167–184. doi:10.1023/A:1007957229865.
8. ^ Baroni, L.; Cenci, L.; Tettamanti, M.; Berati, M. (2007). "Evaluating the environmental impact of various dietary patterns combined with different food production systems". European Journal of Clinical Nutrition 61: 279–286. doi:10.1038/sj.ejcn.1602522.
9. ^ Braun, Charles L.; Sergei N. Smirnov (1993). "Why is water blue?". J. Chem. Educ. 70 (8): 612. http://www.dartmouth.edu/~etrnsfer/water.htm.
10. ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. http://www.phschool.com/el_marketing.html.
11. ^ Kotz, J. C., Treichel, P., & Weaver, G. C. (2005). Chemistry & Chemical Reactivity. Thomson Brooks/Cole.
12. ^ Ball, Philip (14 September 2007). "Burning water and other myths". Nature News. http://www.nature.com/news/2007/070910/full/070910-13.html. Retrieved 2007-09-14.
13. ^ Gary Melnick, Harvard-Smithsonian Center for Astrophysics and David Neufeld, Johns Hopkins University quoted in: "Discover of Water Vapor Near Orion Nebula Suggests Possible Origin of H20 in Solar System (sic)". The Harvard University Gazette. April 23, 1998. http://www.news.harvard.edu/gazette/1998/04.23/DiscoverofWater.html. "Space Cloud Holds Enough Water to Fill Earth's Oceans 1 Million Times". Headlines@Hopkins, JHU. April 9, 1998. http://www.jhu.edu/news_info/news/home98/apr98/clouds.html. "Water, Water Everywhere: Radio telescope finds water is common in universe". The Harvard University Gazette. February 25, 1999. http://www.hno.harvard.edu/gazette/1999/02.25/telescope.html. (linked 4/2007)
14. ^ "MESSENGER Scientists 'Astonished' to Find Water in Mercury's Thin Atmosphere". Planetary Society. 2008-07-03. http://www.planetary.org/news/2008/0703_MESSENGER_Scientists_Astonished_to.html. Retrieved 2008-07-05.
15. ^ Water Found on Distant Planet July 12, 2007 By Laura Blue, Time
16. ^ Water Found in Extrasolar Planet's Atmosphere - Space.com
17. ^ Versteckt in Glasperlen: Auf dem Mond gibt es Wasser - Wissenschaft - Der Spiegel - Nachrichten
18. ^ http://science.nasa.gov/headlines/y2009/24sep_moonwater.htm Water Molecules Found on the Moon, NASA
19. ^ E. Ehlers, T. Krafft., ed (2001). "J. C. I. Dooge. "Integrated Management of Water Resources"". Understanding the Earth System: compartments, processes, and interactions. Springer. p. 116.
20. ^ "Habitable Zone". The Encyclopedia of Astrobiology, Astronomy and Spaceflight. http://www.daviddarling.info/encyclopedia/H/habzone.html.
21. ^ G8 "Action plan" decided upon at the 2003 Evian summit
22. ^ World Health Organization. Safe Water and Global Health.
23. ^ UNEP International Environment (2002). Environmentally Sound Technology for Wastewater and Stormwater Management: An International Source Book. IWA Publishing. ISBN 1843390086. OCLC 49204666.
24. ^ Ravindranath, Nijavalli H.; Jayant A. Sathaye (2002). Climate Change and Developing Countries. Springer. ISBN 1402001045. OCLC 231965991.
25. ^ WBCSD Water Faacts & Trends
26. ^ a b Water Use in the United States, National Atlas.gov
27. ^ Decree relating to the weights and measurements
28. ^ here L'Histoire Du Mètre, La Détermination De L'Unité De Poids
29. ^ Re: What percentage of the human body is composed of water? Jeffrey Utz, M.D., The MadSci Network
30. ^ "Healthy Water Living". http://www.bbc.co.uk/health/healthy_living/nutrition/drinks_water.shtml. Retrieved 2007-02-01.
31. ^ Rhoades RA, Tanner GA (2003). Medical Physiology (2nd ed.). Baltimore: Lippincott Williams & Wilkins. ISBN 0781719364. OCLC 50554808.
32. ^ "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 × 8"? by Heinz Valdin, Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire
33. ^ Drinking Water - How Much?, Factsmart.org web site and references within
34. ^ Food and Nutrition Board, National Academy of Sciences. Recommended Dietary Allowances.. National Research Council, Reprint and Circular Series, No. 122. 1945. pp. 3–18.
35. ^ Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate, Food and Nutrition Board
36. ^ Water: How much should you drink every day? - MayoClinic.com
37. ^ "Conquering Chemistry" 4th Ed. Published 2008
38. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. OCLC 32308337.
39. ^ a b c d e Vaclacik and Christian, 2003
40. ^ a b DeMan, 1999
41. ^ UNESCO, (2006), Water, a shared responsibility. The United Nations World Water Development Report 2.
42. ^ Internet Sacred Text Archive Home

Further reading

Find more about water on Wikipedia's sister projects:
Search Wiktionary Definitions from Wiktionary
Search Wikibooks Textbooks from Wikibooks
Search Wikiquote Quotations from Wikiquote
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Search Wikinews News stories from Wikinews
Search Wikiversity Learning resources from Wikiversity

* John M. DeMan (1999). Principles of Food Chemistry 3rd Edition.
* Vickie A. Vaclavik and Elizabeth W. Christian (2003). Essentials of Food Science 2nd Edition.
* OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
* Franks, F (Ed), Water, A comprehensive treatise, Plenum Press, New York, 1972–1982
* PH Gleick and associates, The World's Water: The Biennial Report on Freshwater Resources. Island Press, Washington, D.C. (published every two years, beginning in 1998.)
* Marks, William E., The Holy Order of Water: Healing Earth's Waters and Ourselves. Bell Pond Books ( a div. of Steiner Books), Great Barrington, MA, November 2001 [ISBN 0-88010-483-X]
* Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", Physics Today 56 (6), p. 40–46 (2003). Downloadable PDF (1.9 MB)

Water as a natural resource

* Anderson (1991). Water Rights: Scarce Resource Allocation, Bureaucracy, and the Environment.
* Maude Barlow, Tony Clarke (2003). Blue Gold: The Fight to Stop the Corporate Theft of the World's Water.
* Gleick, Peter H.. The World's Water: The Biennial Report on Freshwater Resources. Washington: Island Press. (November 10, 2006)| ISBN 9781597261050]
* Miriam R. Lowi (1995). Water and Power: The Politics of a Scarce Resource in the Jordan River Basin. (Cambridge Middle East Library)
* William E. Marks (2001). The Holy Order of Water: Healing Earths Waters and Ourselves.
* Postel, Sandra (1997, second edition). Last Oasis: Facing Water Scarcity. New York: Norton Press.
* Reisner, Marc (1993). Cadillac Desert: The American West and Its Disappearing Water.
* Vandana Shiva (2002). Water Wars: Privatization, Pollution, and Profit. London: Pluto Press [u.a.]. ISBN 0-7453-1837-1. OCLC 231955339.
* Anita Roddick, et al (2004). Troubled Water: Saints, Sinners, Truth And Lies About The Global Water Crisis.
* Marq de Villiers (2003, revised edition). Water: The Fate of Our Most Precious Resource.
* Diane Raines Ward (2002). Water Wars: Drought, Flood, Folly and the Politics of Thirst.
* Worster, Donald (1992). Rivers of Empire: Water, Aridity, and the Growth of the American West.

tank

Tank
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Tank
T-55 skos RB.jpg
T-55 in the Museum of Armament, Poznań
Type Armoured Fighting Vehicle
Place of origin United Kingdom, France
Service history
In service 1916–present
Specifications
Armour Steel plate or composite armour. May be supplemented by explosive reactive armour plating.
Primary
armament Tank gun
Suspension Caterpillar track
For other uses, see Tank (disambiguation).

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility and tactical offensive and defensive capabilities. Firepower is normally provided by a large-calibre main gun in a rotating turret and secondary machine guns, while heavy armour and all-terrain mobility provide protection for the tank and its crew, allowing it to perform all primary tasks of the armoured troops on the battlefield.[1]

Tanks were first introduced by the French and first used in combat by the British during World War I as a means to break the deadlock of trench warfare. They were first deployed at the Battle of Somme in limited numbers. During construction, to conceal their true identity as weapons, they were designated as water carriers for the Mesopotamian campaign and referred to as "tanks" (as in "water tank").

Interwar developments in both design and tactics evolved during World War II, producing important concepts of armoured warfare which persist to this day and were prominently displayed during World War II. The Soviet Union introduced the T-34, one of the best tanks in service throughout the war and one of the forerunners to the main battle tank. Germany introduced blitzkrieg, a strategy which makes use of massed concentrations of tanks supported by artillery and air power to break through the enemy front and cause a complete collapse in enemy resistance.

Today, tanks seldom operate alone, as they are organized into armoured units which involve the support of infantry, who may accompany the tanks in armoured personnel carriers or infantry fighting vehicles. They are also usually accompanied by reconnaissance or ground-attack aircraft.

Due to its formidable capabilities and versatility the battle tank is generally considered a key component of modern armies.[2] However, the prevalence of unconventional and asymmetric warfare have put into question the utility of the armoured force.[3] Ongoing research and development attempts to equip the tank to meet the challenges of the 21st century.
Contents
[hide]

* 1 History
o 1.1 Conception
o 1.2 World War I
o 1.3 Interwar years
o 1.4 World War II
o 1.5 The Cold War arms race
o 1.6 Twenty-first century
* 2 Tank design
o 2.1 Firepower
o 2.2 Protection
+ 2.2.1 Avoiding detection
+ 2.2.2 Armour
o 2.3 Mobility
+ 2.3.1 Water operations
+ 2.3.2 Tank power plants
* 3 Command, control and communications
o 3.1 Early communications
o 3.2 Modern communications and the networked battlefield
* 4 Research and development
* 5 Etymology
* 6 See also
* 7 Notes
* 8 References
* 9 Recommended reading
* 10 External links

[edit] History
Main article: History of the tank
[edit] Conception
The Levavasseur project described a crawler-tracked armoured vehicle equiped with artillery as early as 1903.[4][5]

Apart from Leonardo da Vinci's drawing of a round, tank-like armoured wagon, the first description of a tank-like vehicle and its usefulness in trench warfare is found in an H.G. Wells short story, "The Land Ironclads", in the Strand Magazine, December 1903. The concept of the tank is implicit, however, in two letters published in 1833 in The London United Service Magazine. In the first (January 1833) “A Constant Reader” wrote from Bombay to propose the creation of “Steam Chariots of War”: “The great forte of steam is its passiveness. Secure the boiler and the machinery from the stroke of a cannon-ball, and you might drive a steam-chariot triumphantly through a regiment. Imagine three or four of these machines driven at a galloping speed through a square of infantry; the director might be seated in perfect safety in the rear of the engine, and a body of cavalry, about fifty yards in rear, would enter the furrows ploughed by these formidable chariots, and give the coup-de-grace to the unfortunate infantry. The chariots might be armed with scythes, both in front and flank; and, if the first shock were avoided by the men opening their ranks, they might easily be made sufficiently manageable to wheel round and return on any part of the square which stood firm” (118). In the second letter (May 1833), a correspondent identified only as “C.” discussed the “Application of Steam to Engines of War,” advocating the construction of “Chariots of Iron”—“locomotive engines” covered in “proof iron plate” and capable of running “upon ordinary roads”—for use in battle (118).

Joseph Hawker is attributed as being the father of the modern tank when in 1872, Hawker took out a patent for: 'propelling a road locomotive employing endless flat linked pitch or other chains passing round the rims of the main moving wheels.' The details of his patent reveal clearly the influence his idea had on the whole concept of crawler tractors and tanks employing drive and clutch steering.[6] In 1903, the Levavasseur project describes a caterpillar-based armoured vehicle, and some eight years later, in 1911, two practical tank designs were developed independently by Austrian engineering officer Günther Burstyn and Australian civil engineer Lancelot de Mole, but all were rejected by governmental administrations.

Burstyn designed his tank with a sprung suspension and armed with a single gun located in a revolving turret—a design quite similar to modern tanks—but he was unable to design a track that could carry the weight of the vehicle and propel it at reasonable speed. He submitted his idea of a "land torpedo boat" to the Military Technical Committee in Vienna but the idea was rejected as lacking sufficient merit; he did, however manage to patent his invention (Zl. 252 815 DRP).[7][8]

Around the same time, de Mole designed "a tracked armoured vehicle" and sent his sketches to the British War Office. His idea was rejected, but after the Great War the Royal Commission awarded de Mole £965 for expenses, and in 1920 he was appointed C.B.E.[8][9]
[edit] World War I
Main article: Tanks in World War I
Tanks of WWI.ogg
Play video
Film clip of tanks in Langres, France, during the First World War (1918)
British World War I Mark V tank

Landship development, originally conducted by the Royal Navy under the auspices of the Landships Committee, was sponsored by the First Lord of the Admiralty, Winston Churchill, and proceeded through a number of prototypes, importantly among them the Little Willie, designed by William Ashbee Tritton and Walter Gordon Wilson, as the first-ever completed tracked tank prototype vehicle, culminating in the Mark I tank prototype, named Mother.[10]

The descriptor "tank" is reputed to have evolved from the construction of the early batches by North British Locomotive Company in Glasgow. The order was coded as "special tanks", and ironically much of the work was undertaken in the NBLC Tank shops and the name stuck.[11]

The first tank to engage in battle was designated D1, a British Mark I, during the Battle of Flers-Courcellette on 15 September 1916.[12]

In contrast to World War II, Germany fielded very few tanks during World War I, with only 15 of the A7V type being produced in Germany during the war.[13] The first tank versus tank action took place on 24 April 1918 at Villers-Bretonneux, France, when three British Mark IVs met three German A7Vs. Though both sides revealed serious flaws, the British prevailed.[14]

The French pioneered the use of a full 360º rotation turret in a tank for the first time in 1917, with the creation and deployment of the Renault FT-17 light tank, with the turret containing the tank's main armament.

Mechanical problems, poor mobility and piecemeal tactical deployment limited the military significance of the tank in World War I, and the tank did not fulfil its promise of rendering trench warfare obsolete. Nonetheless, it was clear to military thinkers on both sides that tanks would play a significant role in future conflicts.[10]
[edit] Interwar years
Main article: Tanks (1919–1939)
French Hotchkiss H-39 light tank of 1939

In the interwar period tanks underwent further mechanical development. In terms of tactics, J.F.C. Fuller's doctrine of spearhead attacks with massed tank formations was the basis for work by Heinz Guderian in Germany, Percy Hobart in Britain, Adna R. Chaffee, Jr., in the U.S., Charles de Gaulle in France, and Mikhail Tukhachevsky in the USSR. All came to similar conclusions, but in the Second World War only Germany would initially put the theory into practice on a large scale, and it was their superior tactics and French blunders, not superior weapons, that made blitzkrieg so successful in May 1940.[15] For information regarding tank development in this period, see tank development between the wars.

Germany, Italy and the Soviet Union all experimented heavily with tank warfare during their clandestine and “volunteer” involvement in the Spanish Civil War, which saw some of the earliest examples of successful mechanised combined arms—such as when Republican troops, equipped with Soviet-supplied medium tanks and supported by aircraft, eventually routed Italian troops fighting for the Nationalists in the seven-day Battle of Guadalajara in 1937.[16]
[edit] World War II
Main article: Tanks in World War II
Heinz Guderian, 1941

World War II was the first conflict where armoured vehicles were critical to success on the battlefield and in this period the tank developed rapidly as a weapon system. It showed how an armoured force was capable of achieving victory in an unprecedentedly short amount of time. At the same time however, the development of effective anti-tank weaponry demonstrated that the tank was not invulnerable.

Prior to World War II the tactics and strategy of deploying tank forces underwent a revolution. Heinz Guderian, a tactical theoretician who was heavily involved in the formation of the first independent German tank force, said "Where tanks are, the front is", and this concept became a reality in World War II.[17] Following the Invasion of Poland where tanks performed in a more traditional role in close cooperation with infantry units, in the Battle of France deep independent armoured strategic penetrations were executed by the Germans, a tactic later called blitzkrieg or 'lightning war'. Blitzkrieg made use of innovative combined arms tactics and radios in all of the tanks to provide a level of tactical flexibility and power that surpassed that of the Allied armour. The French Army, with tanks equal or superior to the German tanks in both quality and quantity, employed a linear defensive strategy in which the armoured cavalry units were made subservient to infantry as "support weapons".[15] In addition, they lacked radios in many of their tanks and headquarters[18], which limited their ability to respond to German attacks.

In accordance with blitzkrieg tactics, German tanks bypassed enemy strongpoints and could radio for close air support to destroy them, or leave them to the infantry. A related development, motorized infantry, allowed some of the troops to keep up with the tanks and create highly mobile combined arms forces.[15] The defeat of a major military power within weeks shocked the rest of the world, resulting in an increased focus on tank and anti-tank weapon development.

The North African Campaign also provided an important battleground for tanks, as the flat, desolate terrain with relatively few obstacles or urban environments was ideal for conducting mobile armoured warfare. However, this battlefield also showed the importance of logistics, especially in an armoured force, as the principal warring armies, the German Afrika Korps and the British Eighth Army, often outpaced their supply trains in repeated attacks and counter-attacks on each other, resulting in complete stalemate. This situation would not be resolved until 1942, when during the Second Battle of El Alamein, the Afrika Korps, crippled by disruptions in their supply lines, was forced to retreat by a massively-reinforced Eighth Army, the first in a series of defeats that would eventually lead to the surrender of the remaining Axis forces in Tunisia.
Soviet T-34 tank column advancing near Leningrad, 1942

The German invasion of the Soviet Union, Operation Barbarossa, started with the Soviets having a superior tank design, the T-34.[19] A lack of preparations for the Axis surprise attack, mechanical problems, poor training of the crews and incompetent leadership caused the Soviet machines to be surrounded and destroyed in large numbers. However, interference from Adolf Hitler,[20] the geographic scale of the conflict, the dogged resistance of the Soviet combat troops, Soviet manpower and production capability prevented a repeat of the blitzkrieg of 1940.[21] Despite early successes against the Soviets, the Germans were forced to up-gun their Panzer IVs, and design and build larger and more expensive Panther and Tiger tanks. In doing so, the Wehrmacht denied the infantry and other support arms the production priorities that they needed to remain equal partners with the increasingly sophisticated tanks, in turn violating the principle of combined arms they had pioneered.[2] Soviet developments following the invasion included upgunning the T-34, development of self-propelled anti-tank guns such as the SU-152 and deployment of the IS-2 in the closing stages of the war.
Sherman tanks joining the U.S. Fifth Army forces in the beachhead at Anzio during the Italian Campaign, 1944

When entering World War II, America's mass production capacity enabled her to rapidly construct thousands of relatively cheap M4 Medium tanks. A compromise all round, the Sherman was reliable and formed a large part of the Anglo-American ground forces, but in a tank-versus-tank battle was no match for the Panther or Tiger.[22] Numerical and logistical superiority and the successful use of combined arms allowed the Allies to overrun the German forces during the Battle of Normandy. Upgunned versions with the 76 mm gun M1 and the 17 pounder were introduced to improve the M4's firepower, but concerns about protection remained.

Tank chassis were modified to produce flame tanks, mobile rocket artillery, and combat engineering vehicles for tasks including mine-clearing and bridging. Specialised self-propelled guns were also developed: tank destroyers and assault guns were cheap, stripped down tanks carrying heavy guns, often in a fixed hull mounting. The firepower and low cost of these vehicles made them attractive but as manufacturing techniques improved and larger turret rings made larger tank guns feasible, the gun turret was recognised as the most effective mounting for the main gun to allow movement in a different direction from firing, enhancing tactical flexibility.[15]
[edit] The Cold War arms race
Main article: Tanks in the Cold War
At one time, the Soviet T-72 was the most widely deployed main battle tank across the world[23] and remains in service with the armies of several other countries.

During the Cold War, tension between the Warsaw Pact countries and North Atlantic Treaty Organisation (NATO) countries created an arms race that ensured that tank development proceeded largely as it had during World War II. The essence of tank designs during the Cold War had been hammered out in the closing stages of World War II. Large turrets, capable suspension systems, greatly improved engines, sloped armour and large-calibre (90 mm and larger) guns were standard. Tank design during the Cold War built on this foundation and included improvements to fire control, gyroscopic gun stabilisation, communications (primarily radio) and crew comfort and saw the introduction of laser rangefinders and infrared night vision equipment. Armour technology progressed in an ongoing race against improvements in anti-tank weapons, especially antitank guided missiles like the TOW.

Medium tanks of World War II, evolved into the main battle tank (MBT) of the Cold War and took over the majority of tank roles on the battlefield. This gradual transition occurred in the 1950s and 1960s due to anti-tank guided missiles, sabot ammunition and high explosive anti-tank warheads. World War II had shown that the speed of a light tank was no substitute for armour and firepower and heavy tanks were as vulnerable as medium tanks to newer weapon technology, rendering them obsolete.

In a trend started in World War II, economies of scale led to serial production of progressively upgraded models of all major tanks during the Cold War. For the same reason many upgraded post-World War II tanks and their derivatives (for example, the T-55 and T-72) remain in active service around the world, and even an obsolete tank may be the most formidable weapon on battlefields in many parts of the world.[24] Among the tanks of the 1950s were the British Centurion and Soviet T-54/55 in service from 1946, and the US M48 from 1951.[25] These three vehicles formed the bulk of the armoured forces of NATO and the Warsaw Pact throughout much of the Cold War. Lessons learned from tanks such as the Leopard 1, M48 Patton series, Chieftain, and T-72 led to the contemporary Leopard 2, M1 Abrams, Challenger 2, C1 Ariete, T-90 and Merkava IV.

Tanks and anti-tank weapons of the Cold War era saw action in a number of proxy wars like the Korean War, Vietnam War, Indo-Pakistani War of 1971, Soviet war in Afghanistan and Arab-Israeli conflicts, culminating with the Yom Kippur War. The T-55, for example, has seen action in no fewer than 32 conflicts. In these wars the USA or NATO countries and the Soviet Union or China consistently backed opposing forces. Proxy wars were studied by Western and Soviet military analysts and provided a grim contribution to the Cold War tank development process.
A timeline of major technological advances in tank and infantry anti-tank equipment 1945-2008. The top region shows Western tanks and at the bottom are USSR and Russian tank developments. Selected conflicts are shown along the centre-line.
[edit] Twenty-first century

As of 2005, there were 1,100 M1 Abrams used by the United States Army in the course of the Iraq War, and they have proven to have an unexpectedly high level of vulnerability to roadside bombs.[26] A relatively new type of remotely-detonated mine, the explosively formed penetrator has been used with some success against American armoured vehicles (particularly the Bradley fighting vehicle). However, with upgrades to their armour in the rear, M1s have proven invaluable in fighting insurgents in urban combat, particularly at the Battle of Fallujah, where the Marines brought in two extra brigades.[27] Britain deployed its Challenger 2 tanks to support its operations in southern Iraq.
[edit] Tank design
Schematic diagram of a tank

The three traditional factors determining a tank's effectiveness in battle are its firepower, protection, and mobility. Since the Second World War, the economics of tank production governed by the ease of manufacture and cost, and the impact of a given tank design on logistics and field maintenance capabilities, have also been accepted as important in determining how many tanks a nation can afford to field in its force structure.

No tank design has ever been fielded in significant numbers that proved to be too complex or expensive to manufacture, and made unsustainable demands on the logistics services support of the armed forces. The affordability of the design therefore takes precedence over the field performance characteristics. Nowhere was this principle illustrated better than during the Second World War when two Allied designs, the T-34 and the M4 Sherman, although both simple designs which accepted engineering compromises, were used successfully against more sophisticated designs by Germany which were harder to produce, were more expensive and demanding on overstretched logistics of the Wehrmacht. Given that a tank crew will spend most of its time occupied with maintenance of the vehicle, engineering simplicity has become the primary constraint on tank design since the Second World War despite advances in mechanical, electrical and electronics technologies.

Firepower is the ability of a tank to identify, engage, and destroy. Protection is the tank's ability to resist being detected, engaged, and disabled or destroyed. Mobility includes tactical (short range) movement over the battlefield including over rough terrain and obstacles, as well as strategic (long range) mobility, the ability of the tank to be transported by road, rail, sea, or air to the battlefield.

Tank design is a compromise; it is not possible to maximise firepower, protection and mobility simultaneously. For example, increasing protection by adding armour will result in an increase in weight and therefore decrease mobility; increasing firepower by installing a larger gun will force the designer to sacrifice speed or armour to compensate for the added weight and cost. Even in the case of the Abrams MBT which has good firepower, speed and armour, these advantages are counterbalanced by its notably thirsty engine, which ultimately reduces its range and in a larger sense its mobility.

Since World War II tank development has shifted focus from experimenting with large scale mechanical changes to the tank design to focusing on technological advances in the tank's subsystems to improve its performance. However, a number of novel designs have appeared throughout this period with mixed success, including the Soviet IT-1, the Swedish S-tank, the Israeli Merkava, and the incorporation of autoloaders to reduce the crew complement in a number of tanks.
Further information: Tank classification
[edit] Firepower
Main article: Tank gun
Rifling of a 105 mm Royal Ordnance L7 tank gun.
An M1 Abrams firing.

The main weapon of all modern tanks is a single, large-calibre gun mounted in a fully traversing turret. The typical tank gun is a smoothbore weapon capable of firing armour-piercing kinetic energy penetrators (KEP), also known as armour-piercing discarding sabot (APDS), and/or armour piercing fin stabilised discarding sabot (APFSDS) and high explosive anti-tank (HEAT) shells, and/or high explosive squash head (HESH) and/or anti-tank guided missiles (ATGM) to destroy armoured targets, as well as high explosive (HE) shells for engaging soft targets or fortifications. Canister shot may be used in close or urban combat situations where the risk of hitting friendly forces with shrapnel from HE rounds is unacceptably high.[27]

A gyroscope is used to stabilise the main gun, allowing it to be effectively aimed and fired at the "short halt" or on the move. Modern tank guns are also commonly fitted with insulating thermal jackets to reduce gun-barrel warping caused by uneven thermal expansion, bore evacuators to minimise fumes entering the crew compartment and sometimes muzzle brakes to minimise the effect of recoil on accuracy and rate of fire.

Traditionally, target detection relied on visual identification. This was accomplished from within the tank through telescopic periscopes; occasionally however, tank commanders would open up the hatch to view the outside surroundings, which improved situational awareness but incurred the penalty of vulnerability to sniper fire, especially in jungle and urban conditions. Though several developments in target detection have taken place especially recently, these methods are still common practice.

In some cases spotting rifles were used confirm proper trajectory and range to a target. These spotting rifles were mounted co-axially to the main gun, and fired tracer ammunition ballistically matched to the gun itself. The gunner would track the movement of the tracer round in flight, and upon impact with a hard surface, it would give off a flash and a puff of smoke, after which the main gun was immediately fired. However these have been mostly superseded by laser rangefinding equipment.

Modern tanks also use sophisticated light intensification and thermal imaging equipment to improve fighting capability at night, in poor weather and in smoke. The accuracy of modern tank guns is pushed to the mechanical limit by computerised fire-control systems. A fire-control system uses a laser rangefinder to determine the range to the target, a thermocouple, anemometer and wind vane to correct for weather effects and a muzzle referencing system to correct for gun-barrel temperature, warping and wear. Two sightings of a target with the range-finder enable calculation of the target movement vector. This information is combined with the known movement of the tank and the principles of ballistics to calculate the elevation and aim point that maximises the probability of hitting the target.

Usually, tanks carry smaller calibre armament for short-range defence where fire from the main weapon would be ineffective, for example when engaging infantry, light vehicles or aircraft. A typical complement of secondary weapons is a general-purpose machine gun mounted coaxially with the main gun, and a heavier antiaircraft machine gun on the turret roof. These weapons are often modified variants of those used by infantry, and so utilise the same kinds of ammunition.
[edit] Protection
The British Challenger II is protected by Dorchester armour: second-generation Chobham armour
See also: Anti-tank warfare

The measure of a tank's protection is the combination of its ability to avoid detection, to avoid being hit by enemy fire, its resistance to the effects of enemy fire, and its capacity to sustain damage whilst still completing its objective, or at least protecting its crew. In common with most unit types, tanks are subject to additional hazards in wooded and urban combat environments which largely negate the advantages of the tank's long-range firepower and mobility, limit the crew's detection capabilities and can restrict turret traverse. Despite these disadvantages, tanks retain high survivability against previous-generation Rocket-Propelled Grenades in all combat environments by virtue of their armour.

Almost every advanced Main Battle Tank is fitted with the British 'Chobham Armour' design; with two examples being the American 'M1 Abrams' and the German 'Leopard II'. This is the most advanced armour plating available for any tank (with the exception of the British 'Challenger II') and has been proven against a wide array of Rocket Propelled Weaponry and Exlposives.

However, as effective and advanced as armour plating has become, tank survivability against newer-generation tandem-warhead anti-tank missiles is a concern for military planners.[28]
[edit] Avoiding detection
Further information: Military deception

A tank avoids detection using the doctrine of CCD: camouflage (looks the same as the surroundings), concealment (cannot be seen) and deception (looks like something else).

Working against efforts to avoid detection is the fact that a tank is a large metallic object with a distinctive, angular silhouette that emits copious heat and noise. Consequently, it is difficult to effectively camouflage a hull-up tank in the absence of some form of cover or concealment (e.g., woods). The tank becomes easier to detect when moving (typically, whenever it is in use) due to the large, distinctive auditory, vibration and thermal signature of its power plant. Tank tracks and dust clouds also betray past or present tank movement. Switched-off tanks are vulnerable to infra-red detection due to differences between the thermal conductivity and therefore heat dissipation of the metallic tank and its surroundings. At close range the tank can be detected even when powered down and fully concealed due to the column of warmer air above the tank and the smell of diesel.

Thermal blankets slow the rate of heat emission and camouflage nets use a mix of materials with differing thermal properties to operate in the infra-red as well as the visible spectrum. Camouflage attempts to break up the distinctive appearance and silhouette of a tank. Adopting a turret-down or hull-down position reduces the visible silhouette of a tank as well as providing the added protection of a position in defilade.
[edit] Armour
M4 Sherman tank of 741st Tank Battalion, U.S. First Army, burns in a street in Leipzig, Germany, 1945.
The TUSK for the M1 Abrams is intended to improve survivability in urban environments
Main article: Vehicle armour

To effectively protect the tank and its crew, tank armour must counter a wide variety of antitank threats. Protection against kinetic energy penetrators and high explosive anti-tank (HEAT) shells fired by other tanks is of primary importance, but tank armour also aims to protect against infantry antitank missiles, antitank mines, bombs, direct artillery hits, and (less often) nuclear, biological and chemical threats, any of which could disable or destroy a tank or its crew.

Steel armour plate was the earliest type of armour. The Germans pioneered the use of face hardened steel during World War II and the Soviets also achieved improved protection with sloped armour technology. World War II developments also spelled the eventual doom of homogeneous steel armour with the development of shaped-charge warheads, exemplified by the Panzerfaust and bazooka infantry weapons which were lethally effective, despite some early success with spaced armour. Magnetic mines led to the development of anti-magnetic paste and paint.

British tank researchers took the next step with the development of Chobham armour, or more generally composite armour, incorporating ceramics and plastics in a resin matrix between steel plates, which provided good protection against HEAT weapons. Squash head warheads led to anti-spall armour linings, and KEPs led to the inclusion of exotic materials like a matrix of depleted uranium into a composite armour configuration. Reactive armour consists of small explosive-filled metal boxes that detonate when hit by the metallic jet projected by an exploding HEAT warhead, causing their metal plates to disrupt it. Tandem warheads defeat reactive armour by causing the armour to detonate prematurely. Grenade launchers which can rapidly deploy a smoke screen and the modern Shtora soft-kill countermeasure system provide additional protection by interfering with enemy targeting and fire-control systems.

The latest generation of protective measures for tanks are active protection systems, particularly hard-kill countermeasures. The Israeli TROPHY and Iron Fist, the American Quick Kill, the Soviet Drozd, and Russian Arena systems show the potential to dramatically improve protection for tanks against missiles, RPGs and potentially KEP attacks, but concerns regarding a danger zone for nearby dismounted troops remain.
[edit] Mobility

The mobility of a tank is described by its battlefield or tactical mobility, its operational mobility, and its strategic mobility. Tactical mobility can be broken down firstly into agility, describing the tank's acceleration, braking, speed and rate of turn on various terrain, and secondly obstacle clearance: the tank's ability to travel over vertical obstacles like low walls or trenches or through water. Operational mobility is a function of manoeuvre range; but also of size and weight, and the resulting limitations on options for manoeuvre. For example, in a given sector of front, a T-80 equipped tank formation might have many more potential axes for rapid advance than a heavier M-1 Abrams equipped formation, because of the capacity limits of roads and bridges. Strategic mobility is the relative ease with which a military asset can be transported between theatres of operation and falls within the scope of military logistics. For example, a smaller tank, able to travel through rail tunnels on flatbed rolling stock, might have greater strategic mobility than a larger one.

Tank agility is a function of the weight of the tank due to its inertia while manoeuvring and its ground pressure, the power output of the installed power plant and the tank transmission and track design. In addition, rough terrain effectively limits the tank's speed through the stress it puts on the suspension and the crew. A breakthrough in this area was achieved during World War II when improved suspension systems were developed that allowed better cross-country performance and limited firing on the move. Systems like the earlier Christie or later torsion-bar suspension developed by Ferdinand Porsche dramatically improved the tank's cross-country performance and overall mobility.[29]

A main battle tank is highly mobile and able to travel over most types of terrain due to its continuous tracks and advanced suspension. The tracks disperse the significant weight of the vehicle over a large area, resulting in a ground pressure comparable to that of a walking man.[30] A tank can travel at approximately 40 kilometres per hour (25 mph) across flat terrain and up to 70 kilometres per hour (43 mph) on roads, but due to the mechanical strain this places on the vehicle and the logistical strain on fuel delivery and tank maintenance, these must be considered "burst" speeds that invite mechanical failure of engine and transmission systems. Consequently, wheeled tank transporters and rail infrastructure is used wherever possible for long-distance tank transport. The limitations of long-range tank mobility can be viewed in sharp contrast to that of wheeled armoured fighting vehicles. The majority of blitzkrieg operations were conducted at the pedestrian pace of 5 kilometres per hour (3.1 mph), that only was achieved on the roads of France.[31]
[edit] Water operations
Gepanzerte Pioniermaschine fitted with the same snorkel as used on the Leopard 2 tank

In the absence of combat engineers, most tanks are limited to fording rivers. The typical fording depth for MBTs is approximately 1 metre (3.3 ft), being limited by the height of the engine air intake and driver's position. Modern Soviet tanks and the German Leopard I and Leopard II tanks can ford to a depth of 3-4 meters when properly prepared and equipped with a snorkel to supply air for the crew and engine. Tank crews usually have a negative reaction towards deep fording but it adds considerable scope for surprise and tactical flexibility in water crossing operations by opening new and unexpected avenues of attack.

Amphibious tanks are specially designed or adapted for water operations, but they are rare in modern armies, being replaced by purpose-built amphibious assault vehicles or armoured personnel carriers in amphibious assaults. Advances such as the EFA mobile bridge and MT-55 scissors bridge have also reduced the impediment to tank advance that rivers posed in World War II.[32]
[edit] Tank power plants

The tank's power plant supplies kinetic energy to move the tank, and electric power via a generator to components such as the turret rotation motors and the tank's electronic systems. The tank power plant has evolved from predominantly petrol and adapted large-displacement aeronautical or automotive engines during World Wars I and II, through diesel engines to advanced multi-fuel diesel engines, and powerful (per unit weight) but fuel-hungry gas turbines in the T-80 and M1 Abrams.

Tank power output in context:
Vehicle Power output Power/weight
Mid-sized car: Toyota Camry 2.4L 158 horsepower (118 kW) 106 hp/tonne
Sports car: Lamborghini Murciélago 6.5L 632 horsepower (471 kW) 383 hp/tonne
Racing car: Formula One car 3.0L 950 horsepower (710 kW) 2100 hp/tonne
Main battle tank: Leopard 2, M1 Abrams 1,500 horsepower (1,100 kW) 24.2, 24.5 hp/tonne
Locomotive: SNCF Class T 2000 2,581 horsepower (1,925 kW) 11.5 hp/tonne
[edit] Command, control and communications
German Army Leopard 2A6M incorporates networked battlefield technology

Commanding and coordinating tanks in the field has always been subject to particular problems, particularly in the area of communications, but in modern armies these problems have been partially alleviated by networked, integrated systems that enable communications and contribute to enhanced situational awareness.
[edit] Early communications

Armoured bulkheads, engine noise, intervening terrain, dust and smoke, and the need to operate "buttoned up" are severe detriments to communication and lead to a sense of isolation for small tank units, individual vehicles, and tank crewmen. In World War I, situation reports were sent back to headquarters by releasing carrier pigeons through vision slits and communications between vehicles was accomplished using hand signals, handheld semaphore flags (which were still in use in the Red Army in World War Two) or close range verbal communication.[33]
[edit] Modern communications and the networked battlefield

On the modern battlefield an intercom mounted in the crew helmet provides internal communications and a link to the radio network, and on some tanks an external intercom on the rear of the tank provides communication with co-operating infantry. Radio networks employ radio voice procedure to minimise confusion and "chatter".

A recent development in AFV equipment and doctrine is Network-centric warfare (US) or Network Enabled Capability (UK). This consists of the increased integration of information from the fire control system, laser rangefinder, Global Positioning System and terrain information via hardened milspec electronics and a battlefield network to display all known information on enemy targets and friendly units on a monitor in the tank. The sensor data can be sourced from nearby tanks, planes, UAVs or (in the future) infantry. This improves the tank commander's situational awareness and ability to navigate the battlefield and select and engage targets. In addition to easing the reporting burden by automatically logging all orders and actions, orders are sent via the network with text and graphical overlays.
See also: Military communications and C4ISTAR
[edit] Research and development
Main article: Tank research and development
Graphic representation of the cancelled US Army's XM1202 Mounted Combat System

In terms of firepower, the focus of current R&D is on increased detection capability such as thermal imagers, automated fire control systems and increased muzzle energy from the gun to improve range, accuracy and armour penetration.[34] The most mature future gun technology is the electrothermal-chemical gun.[35] The XM291 electrothermal-chemical tank gun has gone through successful multiple firing sequences on a modified M8 Armored Gun System chassis.[36]

To improve tank protection, one field of research involves making the tank invisible to radar by adapting stealth technologies originally designed for aircraft. A variety of camera and display technologies attempt to improve tank camouflage or even render it invisible. Research is also ongoing in electromagnetic armour systems to disperse or deflect incoming shaped charge jets,[37][38] as well as various forms of active protection systems to prevent incoming projectiles from striking the tank at all.

Mobility may be enhanced in future tanks by the use of diesel-electric or turbine-electric series hybrid drives improving fuel efficiency while reducing the size and weight of the power plant.[39] Furthermore, advances in gas turbine technology, including the use of advanced recuperators,[40] have allowed for reduction in engine volume and mass to less than 1 m3 and 1 metric ton, respectively, while maintaining fuel efficiency similar to that of a diesel engine.[41]

In line with the new doctrine of Network-centric warfare, the modern battle tank shows increasing sophistication in its electronics and communication systems.
[edit] Etymology

The word tank was first applied to the British "landships" in 1915, before they entered service, to keep their nature secret. There are at least three possible explanations of the precise origin of the term:

1. One is it first arose in British factories making the hulls of the first battle tanks: workmen and possible spies were to be given the impression they were constructing mobile water containers or tanks for the British Army, hence keeping the production of a fighting vehicle secret.[10]
2. Another is the term was first used in a secret report on the new motorised weapon presented to Winston Churchill, then First Lord of the Admiralty, by British Army Lt.-Col. Ernest Swinton. From this report, three possible terms emerged: cistern, motor-war car, and tank. Apparently tank was chosen due to its linguistic simplicity.[42]
3. Perhaps the most compelling story comes from Churchill's authoritative biography. To disguise the device, drawings were marked "water carriers for Russia." When it was pointed out this might be shortened to "WCs for Russia," the drawings were changed to "water tanks for Russia." Eventually the weapon was just called a tank.[43]
4. "Tank" was a codename for the vehicle during its development in WW1 to keep it a secret from German spies. The name "Tank", which was a British slang word at the time for a toilet. The name confused those not in on the project but was disliked by the armored corps first commanders.

[edit] See also

* Armoured car (military)
* Armoured engineering vehicle
* Armoured warfare
* Hobart's Funnies
* Hull-down



* Infantry fighting vehicle
* List of armoured fighting vehicles
* List of main battle tanks by country
* Skid steer



* Tank classification
* Tank desant
* Tankette
* Unmanned ground vehicle
* The first tank battle

Tank portal
[edit] Notes

1. ^ von Senger and Etterlin (1960), The World's Armored Fighting Vehicles, p.9.
2. ^ a b House (1984), Toward Combined Arms Warfare:A Survey of 20th-Century Tactics, Doctrine, and Organization
3. ^ Tranquiler, Roger, Modern Warfare. A French View of Counterinsurgency, trans. Daniel Lee, "Pitting a traditional combined armed force trained and equipped to defeat similar military organisations against insurgents reminds one of a pile driver attempting to crush a fly, indefatigably persisting in repeating its efforts."
4. ^ Gougaud, p.101
5. ^ Armoured fighting vehicles of the world‎, p.65
6. ^ http://archive.camborneredruthpacket.co.uk/2007/2/16/82965.html
7. ^ Kenneth Macksey, Tank Facts and Feats, ISBN 0851122043
8. ^ a b Guy Hartcup, The War of Invention: Scientific Developments, 1914-18, ISBN 0080335918
9. ^ Coulthard-Clark, Christopher D., Australian Dictionary of Biography, online edition, http://www.adb.online.anu.edu.au/biogs/A080298b.htm, retrieved 2008-08-26
10. ^ a b c Willmott (2003), First World War
11. ^ McMillan, N: Locomotive Apprentice at the North British Locomotive Company Ltd Glascow Plateway Press 1992
12. ^ Regan (1993), The Guinness Book of More Military Blunders, p.12
13. ^ Willmott (2003), First World War, p.222
14. ^ http://www.firstworldwar.com/diaries/whentankfoughttank.htm
15. ^ a b c d Deighton (1979), Blitzkrieg, From the rise of Hitler to the fall of Dunkirk.
16. ^ Time (1937), Chewed up
17. ^ Cooper and Lucas (1979), Panzer: The Armored Force of the Third Reich, p.9
18. ^ Forty (2004), p.251.
19. ^ Zaloga et al. (1997)
20. ^ Stolfi, Hitler's Panzers East
21. ^ Deighton (1979), Blitzkrieg, From the rise of Hitler to the fall of Dunkirk, p 307
22. ^ Cawthorne (2003), Steel Fist: Tank Warfare 1939 - 45, pp. 211
23. ^ T-72 Main Battle Tank 1974-93 By Steven J. Zaloga, Michael Jerchel, Stephen Sewell
24. ^ Steven Zaloga and Hugh Johnson (2004), T-54 and T-55 Main Battle Tanks 1944–2004, Osprey, 39-41, ISBN 1-84176-792-1, p 43
25. ^ von Senger und Etterlin (1960), The World's Armoured Fighting Vehicles, p. 61, 118 & 183
26. ^ USA Today (2005), Tanks take a beating in Iraq
27. ^ a b USA Today (2005), Tanks adapted for urban fights they once avoided
28. ^ BBC News (2006) Tough lessons for Israeli armour
29. ^ Deighton (1979), Blitzkrieg, From the rise of Hitler to the fall of Dunkirk, pp. 154
30. ^ Thompson and Sorvig (2000), Sustainable Landscape Construction: A Guide to Green Building Outdoors, p.51
31. ^ Deighton (1979), Blitzkrieg, From the rise of Hitler to the fall of Dunkirk, p.180
32. ^ Deighton (1979), Blitzkrieg, From the rise of Hitler to the fall of Dunkirk, pp.234-252
33. ^ Wright 2002, Tank: The Progress of a Monstrous War Machine, p. 48,

To the extent that they communicated at all, the tank crews did so by squeezing carrier pigeons out through a hole in a gun sponson, by brandishing a shovel through the manhole, or by frantically waving coloured discs in the air.

34. ^ Pengelley, Rupert, A new era in tank main armament, pp. 1521 - 1531
35. ^ Hilmes, Rolf (January 30, 1999), "Aspects of future MBT conception". Military Technology 23 (6): 7. Moench Verlagsgesellschaft Mbh.
36. ^ Goodell, Brad (January 1, 2007), "Electrothermal Chemical (ETC) Armament Integration into a Combat Vehicle". IEEE Transaction on Magnetics, Volume 23, Number 1, pp. 456-459.
37. ^ Wickert, Matthias, Electric Armor Against Shaped Charges, pp. 426 - 429
38. ^ Xiaopeng, Li, et al., Multiprojectile Active Electromagnetic Armor, pp. 460 - 462
39. ^ Electric/Hybrid Electric Drive Vehicles for Military Applications, pp. 132 - 144
40. ^ McDonald, Colin F., Gas Turbine Recuperator Renaissance, pp. 1 - 30
41. ^ Koschier, Angelo V. and Mauch, Hagen R., Advantages of the LV100 as a Power Producer in a Hybrid Propulsion System for Future Fighting Vehicles, p. 697
42. ^ Barris (2007), Victory at Vimy: Canada Comes of Age April 9-12 1917, p.116
43. ^ Gilbert (1991), Churchill: A Life, p.298.

[edit] References

* "Electric/Hybrid Electric Drive Vehicles for Military Applications", Military Technology (Moench Verlagsgesellschaft mbH) (9/2007): 132–144, September 2007
* Barris, Ted (2007), Victory at Vimy: Canada Comes of Age April 9-12 1917, Thomas Allen Publishers, pp. 116, ISBN 0887622534; ISBN 9780887622533
* Cawthorne, Nigel (2003), Steel Fist: Tank Warfare 1939-45, London: Arcturus Publishing Ltd., ISBN 0-572-02872-5
* Cooper, Matthew and Lucas, James (1979), Panzer: The Armoured Force of the Third Reich, Book Club Associates
* Deighton, Len (1979), Blitzkrieg: From the rise of Hitler to the fall of Dunkirk, Fakenham: Fakenham Press Limited, ISBN 0-224-01648-2
* DiNardo, Richard L. (January 1986), The First Modern Tank: Gunther Burstyn and His Motorgeschutz, 50, No.1, JSTOR: Society for Military History, pp. 12–15, http://www.jstor.org/pss/1988528
* Col. Eshel, David (2007), Assessing the performance of Merkava Tanks, Defense Update, http://www.defense-update.com/analysis/lebanon_war_3.htm, retrieved 2008-05-16
* Forty, George (2004), Tank Warfare in World War II, London: Constable & Robinson Ltd, ISBN 1-84119-864-1
* Forty, George (2006), The World Encyclopedia of Tanks & Armoured Fighting Vehicles, Lorenz Books, ISBN 0754817415
* Gilbert, Sir Martin (1991), Churchill: A Life, Thomas Allen Publishers, pp. 298, ISBN 0762420812
* Goodell, Brad (January 2007), "Electrothermal Chemical (ETC) Armament System Integration Into a Combat Vehicle", IEEE Transaction on Magnetics (IEEE) 43 (1): 4, doi:10.1109/TMAG.2006.887524
* Hilmes, Rolf (December 2004), "Arming Future MBTs - Some Considerations", Military Technology (Moench Verlagsgesellschaft Mbh) (12/2004): 4
* House, Jonathan M. (1984), Toward Combined Arms Warfare: A Survey of 20th-Century Tactics, Doctrine, and Organization, United States Government Printing, ISBN 9999532357; ISBN 978-9999532358, http://cgsc.leavenworth.army.mil/carl/resources/csi/House/House.asp, retrieved 2008-05-18
* Hunnicutt, R. P. (1984), Patton: A History of the American Main Battle Tank., Presidio, ISBN 0-89141-230-1
* Komarow, Steven (2005), Tanks adapted for urban fights they once avoided, USA Today, http://www.usatoday.com/news/world/2005-03-29-tank-inside_x.htm, retrieved 2008-05-16
* Komarow, Steven (2005), Tanks take a beating in Iraq, USA Today, http://www.usatoday.com/news/world/iraq/2005-03-29-abrams-tank-a_x.htm, retrieved 2008-05-16
* Koschier, Angelo V.; Hagen R. Mauch (2000), "Advantages of the LV100 as a Power Producer in a Hybrid Propulsion System for Future Fighting Vehicles", Journal of Engineering for Gas Turbines and Power 122 (October 2000): 693–698, doi:10.1115/1.1287585
* Marcus, Jonathan (2006), Tough lessons for Israeli armour, BBC News, http://news.bbc.co.uk/2/hi/middle_east/4794829.stm, retrieved 2008-05-26
* McDonald, Colin F. (1990), "Gas Turbine Recuperator Renaissance", Heat Recovery Systems & CHP (Pergamon Press) 10 (1): 1–30, doi:10.1016/0890-4332(90)90246-G
* Pengelley, Rupert (1989), "A new era in tank man armament: The options multiply", Janes International Defense Review (November 1989): 1521–1531
* Regan, Geoffrey (1993), The Guinness Book of More Military Blunders, London: Guinness Publishing, ISBN 0851129617
* Sharoni, Asher H. and Bacon, Lawrence D. (PDF), The Future Combat System (FCS): Technology Evolution Review and Feasibility Assessment, GlobalSecurity.org, http://www.globalsecurity.org/military/library/news/1997/5fcs97.pdf, retrieved 2008-05-26
* Thompson, William J. and Sorvig, Kim (2000), Sustainable Landscape Construction: A Guide to Green Building Outdoors, Island Press, pp. 51, ISBN 1-55963-646-7
* Time Life Books editors (1990), The Armored Fist, Alexandria, Virginia: Time-Life Books, ISBN 0-8094-8609-1; ISBN 0-8094-8608-3; ISBN 0-8094-8704-7
* Chewed Up, Alexandria, Virginia: Time magazine, 5 April 1937, http://www.time.com/time/magazine/article/0,9171,757549,00.html, retrieved 2008-05-16
* Tomes, Robert R. (Spring, 2004), "Relearning Counterinsurgency Warfare" ([dead link]), Parameters (US Army War College) Vol. XXXIV, (No. 1,): 16–28, http://www.army.mil/prof_writing/volumes/volume2/march_2004/3_04_1.html, retrieved 2008-05-26
* von Senger und Etterlin, Dr. F. M. (1960), The World's Armoured Fighting Vehicles, London: Macdonald & Co. (Publishers) Ltd.
* Wickert, Matthias (January 2007), "Electric Armor Against Shaped Charges: Analysis of Jet Distortion With Respect to Jet Dynamics and Current Flow", IEEE Transaction on Magnetics (IEEE) 43 (1): 426–429, doi:10.1109/TMAG.2006.887650
* Willmott, H.P. (2003), First World War, Dorling Kindersley, ISBN 1405300299; ISBN 9781405300292
* Wright, Patrick (2002), Tank: The Progress of a Monstrous War Machine, ISBN 978-0670030705
* Xiaopeng, Li; Meng Tao, Zhao Chun and Li Liyi (January 2007), "Multiprojectile Active Electromagnetic Armor", IEEE Transaction on Magnetics 43 (1): 460–462, doi:10.1109/TMAG.2006.887581
* Zaloga, Steven J. and Grandsen, James (1984), Soviet Tanks and Combat Vehicles of World War Two, London: Arms and Armour Press, ISBN 0-85368-606-8
* Zaloga, Steven J., Kinnear, Jim, Aksenov, Andrey & Koshchavtsev Aleksandr (1997), Soviet Tanks in Combat 1941–45: The T-28, T-34, T-34-85, and T-44 Medium Tanks, Hong Kong: Concord Publication, ISBN 962-361-615-5

[edit] Recommended reading

* Macksey, Kenneth (1976), Tank Warfare, A History of Tanks in Battle, London: Panther, ISBN 0-586-04302-0
* Macksey, Kenneth and Batchelor, John H. (1970), Tank: A History of the Armoured Fighting Vehicle, New York: Scribner, ISBN 0345021665; ISBN 0356034615; ISBN 0684136511
* Ogorkiewicz, Richard M. (1968), Design and Development of Fighting Vehicles, London: MacDonald, ISBN 0-356-01461-4
* Ogorkiewicz, Richard M. (1970), Armoured Forces: A History of Armoured Forces and Their Vehicles, Arms & Armour Press, ISBN 0-85368-049-3
* Ogorkiewicz, Richard M. (1991), Technology of Tanks, Coulsdon, Surrey: Jane's Information Group, ISBN 0-7106-0595-1
* Weeks, John (1975), Men Against Tanks: A History of Anti-Tank Warfare, New York: Mason Charter, ISBN 0-88405-130-7; ISBN 0-7153-6909-1

[edit] External links

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* The Burstyn tank Landships has additional information and a model of Günther Burstyn's Motorengeschütz.
* OnWar's Tanks of World War II Comprehensive specifications and diagrams of World War II tanks.
* Achtung Panzer History of tanks and people of the Panzertruppe.
* Tanks of World War I
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army

ArmyFor other uses, see Army (disambiguation).
Map of the world of the army forms No armed forces No conscription Plan to abolish conscription within 3 years Conscription No information

An army (from Latin armata "armed (things)" via Old French armée, "armed" (feminine), in the broadest sense, is the land-based Military of a nation. It may also include other branches of the military such as the air force via means of aviation corps. Within a national military force, the word Army may also mean a field army, which is an operational formation, usually made up of one or more corps.

A standing army is an army composed of full-time career soldiers who 'stand over', in other words, who do not disband during times of peace. They differ from army reserves who are activated only during such times as war or natural disasters.

In several countries the army is officially called the land army to differentiate it from an air force called the air army, notably France. In such countries, the word "army" on its own retains its connotation of a land force in common usage. The current largest army in the world by number of active troops is the People's Liberation Army of China with 2,250,000 active troops and 800,000 reserve personnel.

By definition, irregular military is understood in contrast to regular armies which grew slowly from personal bodyguards or elite militia.
Contents
[hide]

* 1 History
o 1.1 Sparta
o 1.2 Roman Empire
o 1.3 Early modern
o 1.4 Late Modern
* 2 Armies as armed services
* 3 Field army
o 3.1 Formations
* 4 See also
* 5 References

[edit] History
Main article: Army history
[edit] Sparta

The Spartan Army was one of the earliest profession armies, as men began training at the age of 7[citation needed] and devoted their lives to war until retirement at the age of 60. Unlike other civilizations, whose army had to disband during planting and harvest season, the Spartan serfs, or helots did the manual labour.

This allowed the Spartans to field a full-time army with a campaign season that lasted all year. The Spartan army was largely composed of hoplites, equipped with arms and armour nearly identical to each other, each bearing the Spartan emblem and the colour scarlet.
[edit] Roman Empire

The Roman army was not the first professional army, using the best factors of the Spartan military. It had its origins in the citizen army of the Republic, which was staffed by citizens serving mandatory duty for Rome. Reforms around 100 BC turned the army into a professional structure, still largely filled by citizens, but citizens who served continuously for 25 years before being discharged.

The Romans were also noted for making use of auxiliary troops, non-Romans who served with the legions and filled roles that the traditional Roman military could not fill effectively, such as light skirmish troops and heavy cavalry. Later in the Empire, these auxiliary troops, along with foreign mercenaries, became the core of the Roman military. By the late Empire, tribes such as the Visigoths were paid to serve as mercenaries.

In the earliest Middle Ages it was the obligation of every noble to respond to the call to battle with his own equipment, archers, and infantry. This decentralized system was necessary due to the social order of the time, but could lead to motley forces with variable training, equipment and abilities. The more resources the noble had access to, the better his troops would typically be.

The knights were drawn to battle by feudal and social obligation, and also by the prospect of profit and advancement. Those who performed well were likely to increase their landholdings and advance in the social hierarchy. The prospect of significant income from pillage and ransoming prisoners was also important. For the mounted knight war could be a relatively low risk affair.

As central governments grew in power, a return to the citizen armies of the classical period also began, as central levies of the peasantry began to be the central recruiting tool. England was one of the most centralized states in the Middle Ages, and the armies that fought the Hundred Years' War were mostly paid professionals.

In theory, every Englishman had an obligation to serve for forty days. Forty days was not long enough for a campaign, especially one on the continent.

Thus the scutage was introduced, whereby most Englishmen paid to escape their service and this money was used to create a permanent army. However, almost all high medieval armies in Europe were composed of a great deal of paid core troops, and there was a large mercenary market in Europe from at least the early twelfth century.

As the Middle Ages progressed in Italy, Italian cities began to rely mostly on mercenaries to do their fighting rather than the militias that had dominated the early and high medieval period in this region. These would be groups of career soldiers who would be paid a set rate. Mercenaries tended to be effective soldiers, especially in combination with standing forces, but in Italy they came to dominate the armies of the city states. This made them considerably less reliable than a standing army. Mercenary-on-mercenary warfare in Italy also led to relatively bloodless campaigns which relied as much on maneuver as on battles.
[edit] Early modern

First nation-states lacked the funds needed to maintain standing forces, so they tended to hire mercenaries to serve in their armies during wartime. Such mercenaries typically formed at the ends of periods of conflict, when men-at-arms were no longer needed by their respective governments.

The veteran soldiers thus looked for other forms of employment, often becoming mercenaries. Free Companies would often specialize in forms of combat that required longer periods of training that was not available in the form of a mobilized militia.

As late as the 1650s, most troops were mercenaries. However, after the 16 0's, most states invested in better disciplined and more politically reliable permanent troops. For a time mercenaries became important as trainers and administrators, but soon these tasks were also taken by the state. The massive size of these armies required a large supporting force of administrators.

The newly centralized states were forced to set up vast organized bureaucracies to manage these armies, which some historians argue is the basis of the modern bureaucratic state. The combination of increased taxes and increased centralisation of government functions caused a series of revolts across Europe such as the Fronde in France and the English Civil War.

In many countries, the resolution of this conflict was the rise of absolute monarchy. Only in England and the Netherlands did representative government evolve as an alternative. From the late 1600s, states learned how to finance wars through long term low interest loans from national banking institutions. The first state to master this process was the Dutch Republic. This transformation in the armies of Europe had great social impact. The defense of the state now rested on the commoners, not on the aristocrats.

However, aristocrats continued to monopolise the officer corps of almost all early modern armies, including their high command. Moreover, popular revolts almost always failed unless they had the support and patronage of the noble or gentry classes. The new armies, because of their vast expense, were also dependent on taxation and the commercial classes who also began to demand a greater role in society. The great commercial powers of the Dutch and English matched much larger states in military might.

As any man could be quickly trained in the use of a musket, it became far easier to form massive armies. The inaccuracy of the weapons necessitated large groups of massed soldiers. This led to a rapid swelling of the size of armies. For the first time huge masses of the population could enter combat, rather than just the highly skilled professionals.

It has been argued that the drawing of men from across the nation into an organized corps helped breed national unity and patriotism, and during this period the modern notion of the nation state was born. However, this would only become apparent after the French Revolutionary Wars. At this time, the levée en masse and conscription would become the defining paradigm of modern warfare.

Before then, however, most national armies were in fact composed of many nationalities. In Spain, armies were recruited from all the Spanish European territories including Spain, Italy, Wallonia and Germany.

The French recruited soldiers from Germany, Switzerland and elsewhere as well as from France. Britain recruited Hessian troops until the late 18th century. Irish Catholics made careers for themselves in the armies of many European states.

Prior to the English Civil War in England, the monarch maintained a personal Bodyguard of Yeomen of the Guard and the Honourable Corps of Gentlemen at Arms or 'gentlemen pensioners', and a few locally raised companies to garrison important places such as Berwick on Tweed or Portsmouth (or Calais before it was recaptured by France in 1558).

Troops for foreign expeditions were raised upon an ad-hoc basis. Noblemen and professional regular soldiers were commissioned by the monarch to supply troops, raising their quotas by indenture from a variety of sources. On January 26, 1661 Charles II issued the Royal Warrant that created the genesis of what would become the British Army, although the Scottish and English Armies would remain two separate organizations until the unification of England and Scotland in 1707. The small force was represented by only a few regiments.

After the American Revolutionary War the Continental Army was quickly disbanded as part of the Americans' distrust of standing armies, and irregular state militias became the sole ground army of the United States, with the exception of one battery of artillery guarding West Point's arsenal. However, because of continuing conflict with Native Americans, it was soon realized that it was necessary to field a trained standing army. The first of these, the Legion of the United States, was established in 1791.

Until 1730 the common soldiers of Prussian Army consisted largely of peasantry recruited or impressed from Brandenburg-Prussia, leading many to flee to neighboring countries.[1] In order to halt this trend, Frederick William I divided Prussia into regimental cantons. Every youth was required to serve as a soldier in these recruitment districts for three months each year; this met agrarian needs and added extra troops to bolster the regular ranks.[2]

Russian tsars before Peter I of Russia maintained professional hereditary musketeer corps (streltsy in Russian) that were highly unreliable and undisciplined. In times of war the armed forces were augmented by peasants. Peter I introduced a modern regular army built on German model, but with a new aspect: officers not necessarily from nobility, as talented commoners were given promotions that eventually included a noble title at the attainment of an officer's rank. Conscription of peasants and townspeople was based on quota system, per settlement. Initially it was based on the number of households, later it was based on the population numbers.[3]

The term of service in 18th century was for life. In 1793 it was reduced to 25 years. In 1834 it was reduced to 20 years plus 5 years in reserve and in 1855 to 12 years plus 3 years of reserve.[3][chronology source needed]

The first Ottoman standing army were Janissaries. They replaced forces that mostly comprised tribal warriors (ghazis) whose loyalty and morale could not always be trusted.The first Janissary units were formed from prisoners of war and slaves, probably as a result of the sultan taking his traditional one-fifth share of his army's booty in kind rather than cash.

From the 1380s onwards, their ranks were filled under the devşirme system, where feudal dues were paid by service to the sultan. The "recruits" were mostly Christian youths, reminiscent of Mamelukes.

China organized the Manchu people into the Eight Banner system in the early 17th century. Defected Ming armies formed the Green Standard Army. These troops enlisted voluntarily and for long terms of service.
[edit] Late Modern

Conscription allowed the French Republic to form the La Grande Armée, what Napoleon Bonaparte called "the nation in arms", which successfully battled European professional armies.

Conscription, particularly when the conscripts are being sent to foreign wars that do not directly affect the security of the nation, has historically been highly politically contentious in democracies.

Canada also had a political dispute over conscription during World War II. Similarly, mass protests against conscription to fight the Vietnam War occurred in several countries in the late 1960s.

In developed nations, the increasing emphasis on technological firepower and better-trained fighting forces, the sheer unlikelihood of a conventional military assault on most developed nations, as well as memories of the contentiousness of the Vietnam War experience, make mass conscription unlikely in the foreseeable future.

Russia, as well as many other nations, retains mainly a conscript army. There is also a very rare citizen army as used in Switzerland (see Swiss army).
[edit] Armies as armed services

Western armies are usually subdivided as follows:

* Corps: A Corps usually consists of two or more Divisions and is commanded by a Lieutenant General.
* Division: Each division is commanded by a Major General, and usually holds three Brigades including infantry, artillery, engineers and communications units in addition to logistics (supply and service) support to sustain independent action. Except for the Divisions operating in the mountains, all the Divisions have at least one armored unit, some have even more depending upon their functionality. The basic building block of all ground force combat formations is the infantry division. A typical division would hold three infantry brigades.
* Brigade: A Brigade is under the command of a Brigadier General and comprises three or more Battalions of different units depending on its functionality. An independent brigade would be one that primarily consists of an artillery unit, an infantry unit, an armour unit and logistics to support its actions. Such a brigade is not part of any division and is under direct command of a corps.
* Battalion: Each battalion is commanded by a Lieutenant Colonel who commands roughly 600 to 750 soldiers. This number varies depending on the functionality of the regiment. A regiment comprises either three batteries or four companies - and other arms excluding armoured units that are organised into squadrons each under the command of a major and comprising of individual subunits called sections (which are further divisible into platoons and squads).[4]

[edit] Field army

A field army is composed of a headquarters, army troops, a variable number of corps, and a variable number of divisions. A battle is influenced at the Field Army level by transferring divisions and reinforcements from one corps to another to increase the pressure on the enemy at a critical point. Field armies are controlled by a General or Lieutenant General.
[edit] Formations
German Army soldiers in Bosnia
Standard map symbol for a numbered Army, the 'X's are not substituting the army's number

A particular army can be named or numbered to distinguish it from military land forces in general. For example, the First United States Army and the Army of Northern Virginia. In the British Army it is normal to spell out the ordinal number of an army (e.g. First Army), whereas lower formations use figures (e.g. 1st Division).

Armies (as well as army groups and theaters) are large formations which vary significantly between armed forces in size, composition, and scope of responsibility.

In the Soviet Red Army and the Soviet Air Force, "Armies" were actually corps-sized formations, subordinate to an Army Group-sized "front" in wartime. In peacetime, a Soviet army was usually subordinate to a military district.
[edit] See also

* Military organization
* War
* Military history
* Paramilitary
* Militia
* Mercenary
* List of armies
* List of armies by country
* List of armies by number
* List of countries by size of armed forces

[edit] References

1. ^ Clark, p. 97
2. ^ Koch, p. 88
3. ^ a b Jerome Blum (1971) "Lord and Peasant in Russia: From the Ninth to the Nineteenth Century", ISBN 0691007640, pp. 465,466
4. ^ "" Subdivisions of the army"". http://www.fotw.net/flags/pk%5Eard.html. Retrieved 2007-01-21.

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Retrieved from "http://en.wikipedia.org/wiki/Army"
Categories: Articles lacking chronology/history sources | Field armies | Armies