High explosive squash head
Encyclopedia
High explosive squash head (HESH) 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 tank
s during the Cold War
. It was also used by other military forces, particularly those that acquired the early post-World War 2 British
105 mm Centurion tank
, including Sweden
, India
, and Israel
. In the United States
, it is known as HEP, for "High Explosive, Plastic".
HESH rounds are thin metal shells filled with plastic explosive
and a delayed-action base fuse
. The plastic explosive is "squashed" against the surface of the target on impact and spreads out to form a disc or "pat" of explosive. The base fuze detonates the explosive milliseconds later, creating a shock wave
that, owing to its large surface area and direct contact with the target, is transmitted through the material. In the case of the metal armor of a tank the compression shock wave is conducted through the armour to the point where it reaches the metal/air interface (the hollow crew compartment), where some of the energy is reflected as a tension wave. At the point where the compression and tension waves intersect a high stress zone is created in the metal, causing pieces of steel to be projected off the interior wall at high velocity. This fragmentation by blast wave is known as spalling, with the fragments themselves known as spall
. The spall travels through the interior of the vehicle at high velocity, killing or injuring the crew, damaging equipment, and/or igniting ammunition and fuel. Unlike high explosive anti-tank (HEAT) rounds which are shaped charge
ammunition, HESH shells are not specifically designed to perforate the armour of main battle tanks. HESH shells rely instead on the transmission of the shock wave through the solid steel armour.
HESH ammunition has good general purpose use being effective against most targets, though the round is generally used at relatively lower velocities because high velocity excessively disperses the pat of explosive. While only effective against tanks without spaced armor or spall liners, the round is still highly favored for combat demolition
purposes. The flattened high-velocity explosive pat is capable of destroying concrete constructions much faster than a HEAT round (which is designed for armor penetration), and without the dangerous fragmentation of a traditional high explosive
(HE) fragmentation round.
in the 1940s for the British war effort, originally as an anti-fortification
"wallbuster" munition for use against concrete
. He also led British developments in recoilless rifle
s as a means to deliver the shell. An early application of the HESH principle was the Royal Engineers
AVRE
's 165mm demolition gun.
HESH was found to be surprisingly effective against metallic armour as well, although the British already had effective weapons using HEAT, such as the PIAT
. HESH was for some time a competitor to the more common HEAT round, again in combination with recoilless rifles as infantry weapons and was effective against tanks such as the T-55
and T-62
. Later versions of T-55 and T-62 tanks contained a layer of spall liner, decreasing the effectiveness of the HESH round. Britain also devised anti-tank guided missile
s in the 1960s with HESH warheads such as the Malkara
, although most subsequent designs used variants of the HEAT concept.
From the 1970s onwards tank armour design has tended towards layered composites of hard metal and heat-resistant materials. This type of armour is a poor conductor of the shock wave. "Spall liners", made of materials such as Kevlar
, are commonly fitted to the interior surface of the armour where it acts to retain any spall that does occur. Another reason for the declining use of HESH rounds is the switch by most armies to smoothbore
cannon, since a HESH shell relies upon spin for accuracy. The British Army has kept rifled
tank gun
s longer than many partly to maintain HESH ammunition capability, though the Challenger 2 is intended to be converted to a smoothbore in the interests of ammunition commonality with NATO partners. HESH rounds are still carried today by armoured engineer vehicles
; they are typically intended for use against fortification
s rather than armoured fighting vehicle
s. A 165 mm HESH round is used by the United States Army
for the main gun of the M728 Combat Engineer Vehicle
, an M60 tank
equipped with a bulldozer
blade. Similarly the British Centurion AVRE (Armoured Vehicle Royal Engineers
) was equipped with a short 165 mm gun solely for a 29 kg HESH shell.
Amongst other ammunition types, the Stryker Mobile Gun System
variant is to be equipped with a 105 mm HESH round for demolition and bunker-busting purposes. Argentina
's TAM
medium tanks, India's Arjun Tanks, and Canada
's Leopard C1 and Leopard C2 main battle tanks (mounted with the same 105 mm gun as the Centurion) can also fire HESH rounds.
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
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....
. It was fielded chiefly by the British Army
British Army
The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...
as the main explosive round of its 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 during the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
. It was also used by other military forces, particularly those that acquired the early post-World War 2 British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
105 mm Centurion tank
Centurion tank
The Centurion, introduced in 1945, was the primary British main battle tank of the post-World War II period. It was a successful tank design, with upgrades, for many decades...
, including Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, 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...
, and Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, it is known as HEP, for "High Explosive, Plastic".
Plastic explosive
Plastic explosive is a specialised form of explosive material. It is a soft and hand moldable solid material. Plastic explosives are properly known as putty explosives within the field of explosives engineering....
and a delayed-action base fuse
Fuse
The word fuse has several meanings:* Fuse , a device used in electrical systems to protect against excessive current....
. The plastic explosive is "squashed" against the surface of the target on impact and spreads out to form a disc or "pat" of explosive. The base fuze detonates the explosive milliseconds later, creating a shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
that, owing to its large surface area and direct contact with the target, is transmitted through the material. In the case of the metal armor of a tank the compression shock wave is conducted through the armour to the point where it reaches the metal/air interface (the hollow crew compartment), where some of the energy is reflected as a tension wave. At the point where the compression and tension waves intersect a high stress zone is created in the metal, causing pieces of steel to be projected off the interior wall at high velocity. This fragmentation by blast wave is known as spalling, with the fragments themselves known as spall
Spall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
. The spall travels through the interior of the vehicle at high velocity, killing or injuring the crew, damaging equipment, and/or igniting ammunition and fuel. Unlike high explosive anti-tank (HEAT) rounds which are 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...
ammunition, HESH shells are not specifically designed to perforate the armour of main battle tanks. HESH shells rely instead on the transmission of the shock wave through the solid steel armour.
HESH ammunition has good general purpose use being effective against most targets, though the round is generally used at relatively lower velocities because high velocity excessively disperses the pat of explosive. While only effective against tanks without spaced armor or spall liners, the round is still highly favored for combat demolition
Demolition
Demolition is the tearing-down of buildings and other structures, the opposite of construction. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use....
purposes. The flattened high-velocity explosive pat is capable of destroying concrete constructions much faster than a HEAT round (which is designed for armor penetration), and without the dangerous fragmentation of a traditional high explosive
Explosive material
An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure...
(HE) fragmentation round.
History
HESH was developed by Charles Dennistoun BurneyCharles Dennistoun Burney
Sir Charles Dennistoun Burney, 2nd Baronet was an English aeronautical engineer, private inventor and Conservative Party politician....
in the 1940s for the British war effort, originally as an anti-fortification
Bunker
A military bunker is a hardened shelter, often buried partly or fully underground, designed to protect the inhabitants from falling bombs or other attacks...
"wallbuster" munition for use against concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
. He also led British developments in recoilless rifle
Recoilless rifle
A recoilless rifle or recoilless gun is a lightweight weapon that fires a heavier projectile than would be practical to fire from a recoiling weapon of comparable size. Technically, only devices that use a rifled barrel are recoilless rifles. Smoothbore variants are recoilless guns...
s as a means to deliver the shell. An early application of the HESH principle was the Royal Engineers
Royal Engineers
The Corps of Royal Engineers, usually just called the Royal Engineers , and commonly known as the Sappers, is one of the corps of the British Army....
AVRE
Avre
Avre may refer to:*Avre , a river in northwestern France, tributary of the Eure*Avre , a river in northern France, tributary of the Somme*Armoured Vehicle Royal Engineers, a military vehicle of the British Army...
's 165mm demolition gun.
HESH was found to be surprisingly effective against metallic armour as well, although the British already had effective weapons using HEAT, such as the PIAT
PIAT
The Projector, Infantry, Anti Tank was a British hand-held anti-tank weapon developed during the Second World War. The PIAT was designed in 1942 in response to the British Army's need for a more effective infantry anti-tank weapon, and entered service in 1943.The PIAT was based on the spigot...
. HESH was for some time a competitor to the more common HEAT round, again in combination with recoilless rifles as infantry weapons and was effective against tanks such as the T-55
T-55
The T-54 and T-55 tanks were a series of main battle tanks designed in the Soviet Union. The first T-54 prototype appeared in March 1945, just before the end of the Second World War. The T-54 entered full production in 1947 and became the main tank for armored units of the Soviet Army, armies of...
and T-62
T-62
The T-62 is a Soviet main battle tank, a further development of the T-55. Its 115 mm gun was the first smoothbore tank gun in use.The T-62 was produced between 1961 and 1975. It became a standard tank in the Soviet arsenal, partly replacing the T-55, although that tank continued to be...
. Later versions of T-55 and T-62 tanks contained a layer of spall liner, decreasing the effectiveness of the HESH round. Britain also devised anti-tank guided missile
Anti-tank guided missile
An anti-tank missile , anti-tank guided missile , anti-tank guided weapon or anti-armor guided weapon is a guided missile primarily designed to hit and destroy heavily-armored military vehicles....
s in the 1960s with HESH warheads such as the Malkara
Malkara missile
The Malkara missile was one of the earliest anti-tank guided missiles . It was jointly developed by Australia and the United Kingdom between 1951 and 1954, and was in service from 1958 until gradually replaced by the Swingfire missile in the late 1960s...
, although most subsequent designs used variants of the HEAT concept.
From the 1970s onwards tank armour design has tended towards layered composites of hard metal and heat-resistant materials. This type of armour is a poor conductor of the shock wave. "Spall liners", made of materials such as Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
, are commonly fitted to the interior surface of the armour where it acts to retain any spall that does occur. Another reason for the declining use of HESH rounds is the switch by most armies to 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:...
cannon, since a HESH shell relies upon spin for accuracy. The British Army has kept rifled
Rifling
Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...
tank gun
Tank gun
A tank gun is the main armament of a tank. Modern tank guns are large-caliber high-velocity guns, capable of firing kinetic energy penetrators, high explosive anti-tank rounds, and in some cases guided missiles. Anti-aircraft guns can also be mounted to tanks.-Overview:Tank guns are a specific...
s longer than many partly to maintain HESH ammunition capability, though the Challenger 2 is intended to be converted to a smoothbore in the interests of ammunition commonality with NATO partners. HESH rounds are still carried today by armoured engineer vehicles
Combat engineering vehicle
Military engineering vehicles are vehicles built for the construction work or for the transportation of combat engineers on the battlefield. These vehicles can range from civilian equipment to purpose built military vehicles....
; they are typically intended for use against fortification
Fortification
Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...
s rather than armoured fighting vehicle
Armoured fighting vehicle
An armoured fighting vehicle is a combat vehicle, protected by strong armour and armed with weapons. AFVs can be wheeled or tracked....
s. A 165 mm HESH round is used 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...
for the main gun of the M728 Combat Engineer Vehicle
M728 Combat Engineer Vehicle
The M728 Combat Engineer Vehicle is a military engineering vehicle based on an M60A1 Patton main battle tank chassis with a hydraulically operated dozer blade mounted on the front effectively functioning as an armored bulldozer, plus an A-frame crane boom hinged on either side of the turret and a...
, an M60 tank
M60 Patton
The 105 mm Gun Full Tracked Combat Tank, M60, also known unofficially as the M60 Patton, is a first-generation main battle tank introduced in December 1960. It was widely used by the U.S. and its Cold War allies, especially those in NATO, and remains in service throughout the world today...
equipped with a bulldozer
Bulldozer
A bulldozer is a crawler equipped with a substantial metal plate used to push large quantities of soil, sand, rubble, etc., during construction work and typically equipped at the rear with a claw-like device to loosen densely-compacted materials.Bulldozers can be found on a wide range of sites,...
blade. Similarly the British Centurion AVRE (Armoured Vehicle Royal Engineers
Armoured Vehicle Royal Engineers
Armoured Vehicle Royal Engineers is the title given to a series of armoured vehicles operated by the Royal Engineers for the purpose of battlefield engineer support. These vehicles have been either purpose-built or post-production modifications of existing tank-based armoured vehicles...
) was equipped with a short 165 mm gun solely for a 29 kg HESH shell.
Amongst other ammunition types, the Stryker Mobile Gun System
Stryker Mobile Gun System
The Stryker Mobile Gun System is an eight-wheeled armored fighting vehicle mounting a 105 mm tank gun, based on the Canadian LAV III light-armored vehicle. It is in service with the United States and was also being considered for adoption by several other countries, including Canada.- Design...
variant is to be equipped with a 105 mm HESH round for demolition and bunker-busting purposes. Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
's TAM
TAM (tank)
The Tanque Argentino Mediano , or TAM, is the main battle tank in service with the Argentine Army. Lacking the experience and resources to design a tank, the Argentine Ministry of Defense contracted German company Thyssen-Henschel...
medium tanks, India's Arjun Tanks, and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
's Leopard C1 and Leopard C2 main battle tanks (mounted with the same 105 mm gun as the Centurion) can also fire HESH rounds.