A high-explosive squash head (HESH), in British terminology, or a high-explosive plastic/plasticized (HEP), in US-American terminology, is a type of explosive projectile with plastic explosive that conforms to the surface of a target before detonating, which improves the transfer of explosive energy to the target. Squash head projectiles are similar to high-explosive projectiles and are well suited to many of the same targets. However, while HESH projectiles are not armour-piercing, they can defeat armored targets by causing spall, which can injure or kill a vehicle's occupants or detonate some types of ammunition.

HESH ammunition is effective for general purpose use, being effective against most targets, though the round is generally used at relatively low velocities (generally under ) because a high velocity excessively disperses the pat of explosive. While only effective against tanks without spaced armour or spall liners, the round is still favoured for combat demolition purposes. The flattened high-velocity explosive pat can better destroy concrete constructions than a HEAT round (which is designed to penetrate armour), and without the dangerous fragmentation of a traditional high explosive (HE) fragmentation round.

History

HESH was developed by Dennistoun Burney 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 rifles as a means to deliver the shell. An early application of the HESH principle post WWII was the L9 165 mm demolition gun fitted to AVRE combat engineer vehicles.

HESH was found to be surprisingly effective against metallic armour as well as concrete structures. It was widely used as a primary round in most large calibre rifled guns.

Users

thumb|Japanese 105 mm Type B HESH shell for the [[Royal Ordnance L7 rifled gun in use on the Type 74 tank]]

thumb|[[US Navy technicians building a munitions disposal for HESH (HEP) shells]]

HESH rounds were fielded mainly by the British Army as the main explosive round of its main battle tanks during the Cold War. It was also used by other military forces, especially those that acquired the early post-World War II British Royal Ordnance L7A1 tank gun, including Germany, India, Israel, and Sweden.

Since the 1980s, HESH ammunition has increasingly lost favour as armour designs have trended towards layered composites of hard metal and heat-resistant materials. This type of armour conducts shock waves poorly. Anti-spalling devices (spall liners), made of materials such as Kevlar, are commonly fitted to the interior surface of modern armoured vehicles to minimise spalling effects. Another reason for the declining use of HESH rounds is the preference of most armies using smoothbore guns due to the usage of powerful armour-piercing fin-stabilized discarding sabot, which would significantly decrease the rifled gun's barrel life.

British Challenger 1 and Challenger 2 tanks, and India's Arjun tank (which has the same rifled gun as the UK's MBTs) use HESH rounds as their primary ammunition. Amongst other ammunition types, the Stryker Mobile Gun System variant is to be equipped with a HESH round for demolition and bunker-busting purposes. Argentina's TAM medium tanks, Canada's Leopard C1 and Leopard C2 main battle tanks (all of which mount the same gun as the Centurion), the Australian Leopard AS1 main battle tank, and the Chinese VT-4 main battle tank (which mounts a smoothbore gun) all use HESH rounds.

HESH rounds are also carried by armoured engineer vehicles; they are typically intended for use against fortifications rather than armoured fighting vehicles. A 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 UK's Centurion AVRE was equipped with a short gun solely for a HESH shell.

See also

  • Munroe effect
  • High-explosive incendiary
  • Mine shell

References

pl:Amunicja przeciwpancerna#przeciwpancerny pocisk odkształcalny