A kinetic energy penetrator (also known as a KE weapon) is a type of ammunition

Ammunition

Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

 which, like a bullet

Bullet

A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...

, does not contain explosives and uses kinetic energy

Kinetic energy

The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 to penetrate the target.

The term can apply to any type of armour

Vehicle armour

Military vehicles are commonly armoured to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships....

-piercing shot but typically refers to a modern type of armour piercing weapon, the armour-piercing fin-stabilized discarding sabot

Sabot

A sabot is a device used in a firearm or cannon to fire a projectile, such as a bullet, that is smaller than the bore diameter, or which must be held in a precise position. The term is also applied to a battery stub case, a device used similarly to make a small electrical battery usable in a...

(APFSDS), a type of long-rod penetrator (LRP), and not to small arms

Small arms

Small arms is a term of art used by armed forces to denote infantry weapons an individual soldier may carry. The description is usually limited to revolvers, pistols, submachine guns, carbines, assault rifles, battle rifles, multiple barrel firearms, sniper rifles, squad automatic weapons, light...

 bullets.

The opposite technique to KE-penetrators uses chemical energy penetrators. There are two types of these shell

Shell (projectile)

A shell is a payload-carrying projectile, which, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot . Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used...

s in use: high explosive anti-tank (HEAT) and high explosive squash head

High explosive squash head

High explosive squash head is a type of explosive ammunition that is effective against buildings and is also used against tank armour. It was fielded chiefly by the British Army as the main explosive round of its main battle tanks during the Cold War...

 (HESH). They have been widely used against armour in the past and still have a role but are less effective against modern composite armour

Composite armour

Composite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration...

, such as Chobham

Chobham armour

Chobham armour is the name informally given to a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey, England...

 or Kanchan

Kanchan armour

Kanchan Armour is the name informally given to a modular composite armour indigenously developed by India. The Kanchan Armour got its name from Kanchan Bagh , Hyderabad, Andhra Pradesh, India where the Defence Metallurgical Research Laboratory is located....

, as used on main battle tank

Main battle tank

A main battle tank , also known as a battle tank or universal tank, is a tank that fills the heavy direct fire role of many modern armies. They were originally conceived to replace the light, medium, heavy and super-heavy tanks. Development was spurred onwards in the Cold War with the development...

s today.

The principle of the kinetic energy penetrator is that it uses its kinetic energy, which is a function of mass

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 and velocity, to force its way through armour. If the armor is defeated, the heat and spalling (particle spray) generated by the penetrator going through the armor, and the pressure wave that would develop, is what would destroy the target.

The modern KE weapon maximizes KE and minimizes the area over which it is delivered by:

• being fired with a very high muzzle velocity
  Muzzle velocity
  Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
  
  
• concentrating the force in a small impact area while still retaining a relatively large mass
• maximizing the mass of whatever (albeit small) volume is occupied by the projectile—that is, using the densest
  Density
  The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
  
   metals practical, which is one of the reasons depleted uranium
  Depleted uranium
  Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
  
   is often used.

This has led to the current designs which resemble a long metal arrow

Arrow

An arrow is a shafted projectile that is shot with a bow. It predates recorded history and is common to most cultures.An arrow usually consists of a shaft with an arrowhead attached to the front end, with fletchings and a nock at the other.- History:...

.

History

The first cannon fired kinetic energy ammunition. First these were round balls of worked stone, then round balls of metal. From the beginning, combining high muzzle energy with projectile density and hardness have been the foremost factors in the design of such weapons. Similarly, the foremost purpose of such weapons has generally been to defeat armour or other defensive structures, whether stone castle walls, ship timbers, or modern tank armour. Chemical energy ammunition in its various forms has consistently been the choice for those weapons which due to various factors of their design could not generate the high muzzle energy needed by a kinetic energy weapon.

The development of the modern KE penetrator combines two aspects of artillery design; high muzzle velocity and concentrated force. High muzzle velocity is achieved by using a projectile with a low mass and large base area in the gun barrel. Firing a small size projectile wrapped in a lightweight outer shell, called a sabot

Sabot

A sabot is a device used in a firearm or cannon to fire a projectile, such as a bullet, that is smaller than the bore diameter, or which must be held in a precise position. The term is also applied to a battery stub case, a device used similarly to make a small electrical battery usable in a...

, raises the muzzle velocity. Once the shell clears the barrel, the sabot is no longer needed and falls off in pieces. This leaves the projectile traveling at high velocity with a smaller cross-sectional area and reduced aerodynamic drag during the flight to the target (see external ballistics

External ballistics

External ballistics is the part of the science of ballistics that deals with the behaviour of a non-powered projectile in flight. External ballistics is frequently associated with firearms, and deals with the behaviour of the bullet after it exits the barrel and before it hits the target.-Forces...

 and terminal ballistics

Terminal ballistics

Terminal ballistics, a sub-field of ballistics, is the study of the behavior of a projectile when it hits its target. It is often referred to as stopping power when dealing with human or other living targets. Terminal ballistics is relevant both for small caliber projectiles as well as for large...

). Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 developed modern sabots under the name "Treibspiegel" ("propulsion mirror") to give extra altitude to their anti-aircraft guns

Anti-aircraft warfare

NATO defines air defence as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be to protect naval, ground and air forces...

 during the Second World War

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. Before this, primitive wooden sabots had been used for centuries in the form of a wooden plug attached to or breech loaded before cannon balls in the barrel, placed between the propellant charge and the projectile. The name "sabot" is the French word for clog

Clog (shoe)

A clog is a type of footwear made in part or completely from wood.The Oxford English Dictionary defines a clog as a "thick piece of wood", and later as a "wooden soled overshoe" and a "shoe with a thick wooden sole"....

 (a wooden shoe traditionally worn in some European countries). According to one theory, the word "sabotage

Sabotage

Sabotage is a deliberate action aimed at weakening another entity through subversion, obstruction, disruption, or destruction. In a workplace setting, sabotage is the conscious withdrawal of efficiency generally directed at causing some change in workplace conditions. One who engages in sabotage is...

" is derived from this specific meaning of "sabot".

Concentration of force into a smaller area was attained by replacing the single metal (usually steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

) shot with a composite shot using two metals, a heavy core (based on tungsten

Tungsten

Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

) inside a lighter metal outer shell. These designs were known as Armour Piercing Composite Rigid (APCR). On impact, the core had a much more concentrated effect than plain metal shot of the same weight and size. However, the air resistance and other effects were the same as for the shell of identical size.

Between 1941 and 1943, the British combined the two techniques in the armour-piercing discarding sabot

Armour-piercing discarding sabot

Armour-piercing discarding sabot is a type of kinetic energy projectile fired from a gun to attack armoured targets. APDS rounds are sabot rounds and were commonly used in large calibre tank guns, but have now been superseded by armour-piercing fin-stabilized discarding sabot projectiles in such...

 (APDS) round. The sabot replaced the outer metal shell of the APCR. While in the gun the shot had a large base area to get maximum acceleration from the propelling charge but once outside, the sabot fell away to reveal a heavy shot with a small cross-sectional area. High Velocity Armor Piercing (HVAP) rounds were also introduced by the United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

, and were primarily used by tank destroyer

Tank destroyer

A tank destroyer is a type of armored fighting vehicle armed with a gun or missile launcher, and is designed specifically to engage enemy armored vehicles...

s.

Modern design

The APDS was initially the main design of KE penetrator. The logical progression was to make the shot longer and thinner to concentrate the kinetic energy in a smaller area. However a long, thin rod is aerodynamically unstable; it tends to tumble in flight and is less accurate. Traditionally, shells were given stability in flight from the rifling of the gun barrel, which imparts a spin to the round. Up to a certain limit this is effective, but once the projectile's length is more than six or seven times its diameter, rifling becomes less effective. Adding fins like the fletching of an arrow to the base gives the round stability, hence Armour-Piercing Fin-Stabilized Discarding Sabot (APFSDS). The spin from rifling decreases the effective penetration of these rounds (rifling diverts some of the linear kinetic energy to rotational kinetic energy, thus decreasing the round's velocity and impact energy) and so they are generally fired from smoothbore

Smoothbore

A smoothbore weapon is one which has a barrel without rifling. Smoothbores range from handheld firearms to powerful tank guns and large artillery mortars.-History of firearms and rifling:...

 guns; a practice that has been taken up by Israel — a major supplier of "arrow" rounds — China

People's Republic of China

China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

, France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, Pakistan

Pakistan

Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, and the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in their tanks. Another reason for the use of smoothbore guns is that shaped charge

Shaped charge

A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to cut and form metal, to initiate nuclear weapons, to penetrate armor, and in the oil and gas industry...

 HEAT

Heat

In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 munitions lose much of their effect to rotation. APFSDS can still be fired from rifled guns but the sabot is of a modified design incorporating bearings to isolate the spin of the sabot in the barrel from the round itself, so far as practicable. Rifled guns have been kept in use by some nations (the UK and India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, for example) because they are able to fire other ammunition such as HESH rounds with greater accuracy. However, the rifling wears down under regular APFSDS use and requires more maintenance. For these reasons the British Challenger 2 is being trialled with a Rheinmetall 120mm smoothbore gun.

KE penetrators for modern tank

Tank

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

s are commonly 2–3 cm in diameter, and 50–60 cm long; as more modern penetrators are developed, their length tends to increase and the diameter to decrease. However the development of heavy forms of reactive armour such as the Soviet, later Russian, Kontakt-5

Kontakt-5

Kontakt-5 is a type of third-generation explosive reactive armour originating in the Soviet Union. It is the first type of ERA which is effectively able to defeat modern armour-piercing fin-stabilized discarding sabot rounds....

 which were designed to shear long rod penetrators, has prompted the reversal of this trend in the newest U.S. rounds. To maximize the amount of kinetic energy released on the target, the penetrator must be made of a dense

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 material, such as tungsten carbide

Tungsten carbide

Tungsten carbide is an inorganic chemical compound containing equal parts of tungsten and carbon atoms. Colloquially, tungsten carbide is often simply called carbide. In its most basic form, it is a fine gray powder, but it can be pressed and formed into shapes for use in industrial machinery,...

 or depleted uranium

Depleted uranium

Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

 (DU) alloy (Staballoy

Staballoy

]Staballoy is the name of two different classes of metal alloys, one class typically used for munitions and a different class developed for drilling rods....

). The hardness of the penetrator is of less importance, but is still a factor as abrasion is a major component of the penetrator defeat mechanism. As DU is itself not particularly hard, it is alloyed with nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

, zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, or both. DU is pyrophoric; the heated fragments of the penetrator ignite after impact on contact with air, setting fire to fuel and/or ammunition in the target vehicle, thereby compensating for the lack of an explosive warhead in the penetrator. Additionally, DU penetrators exhibit significant adiabatic shear band

Adiabatic shear band

Adiabatic shear band is a term used in physics, mechanics and engineering.Since the 1960s adiabatic shear bands have been studied extensively because of their importance as a failure mode in areas such as metal forming and cutting, various types of ballistic impact, as well as vehicle crashes.An...

 formation. A common misconception is that, during impact, fractures along these bands cause the tip of the penetrator to continuously shed material, maintaining the tip's conical shape, whereas other materials such as unjacketed tungsten tend to deform into a less effective rounded profile, an effect called "mushrooming". Actually, the formation of adiabatic shear bands means that the sides of the "mushroom" tend to break away earlier, leading to a smaller head on impact, though it will still be significantly "mushroomed". Tests have shown that the hole bored by a DU projectile is of a narrower diameter than for a similar tungsten projectile.

Typical velocities of APFSDS rounds vary between manufacturers and muzzle length/types. As a typical example, the American General Dynamics

General Dynamics

General Dynamics Corporation is a U.S. defense conglomerate formed by mergers and divestitures, and as of 2008 it is the fifth largest defense contractor in the world. Its headquarters are in West Falls Church , unincorporated Fairfax County, Virginia, in the Falls Church area.The company has...

 KEW-A1 has a muzzle velocity

Muzzle velocity

Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...

 of 1,740 m/s (5,700 ft/s). This compares to 914 m/s (3,000 ft/s) for a typical rifle (small arms) round. APFSDS rounds generally operate in the range of 1,400 to 1,900 m/s. The sabots also travel at such a high velocity that upon separation, they may continue for many hundreds of metres at speeds that can be lethal to troops and damage light vehicles.

The counterpart of APFSDS in rifle ammunition is the saboted flechette

Flechette

A flechette is a pointed steel projectile, with a vaned tail for stable flight. The name comes from French , "little arrow" or "dart", and sometimes retains the acute accent in English: fléchette.-Bulk and artillery use:...

. A rifle firing flechettes, the Special Purpose Individual Weapon

Special Purpose Individual Weapon

The Special Purpose Individual Weapon was a long-running United States Army program to develop, in part, a workable flechette-based "rifle", though other concepts were also involved...

, was under development for the U.S. Army, but the project was abandoned.