High - explosive squash head 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 fuze . 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 low velocities because high velocity excessively disperses the pat of explosive . While only effective against tanks without spaced armour 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 . History . HESH was developed by Charles 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 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 . Since the 1970s , HESH ammunitions have increasingly fallen out of favor as armoring designs have trended towards layered composites of hard metal and heat - resistant materials . This type of armor is a poor conductor of shock waves . The adoption of anti - spalling devices ( " spall liners " ) , made of materials such as Kevlar , are commonly fitted to the interior surface of modern armored vehicles to mitigate spalling effects . Another reason for the declining use of HESH rounds is the preference of most armies for smoothbore cannons , since a HESH shell is reliant upon rifling ( spin ) to be accurate . Rifled tank gun s have fallen out of favor in modern battle tanks ; however , the British Army has persisted with a rifled cannon on their Challenger 1 and Challenger 2 battle tanks partly to preserve the general purpose capability of HESH ammunition . Nevertheless , the British Army had planned for a conversion to the more versatile smoothbore cannons , but the project was cancelled due to budget constraints . This would have allowed them to take advantage of commonality with NATO partners and the greater availability of smoothbore ammunition types such as high - explosive ( HE ) , time - fuzed and canister shot . British rifled tanks have been limited to two ammunition types : a kinetic energy penetrator and HESH . 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 tank , 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 .