High Explosive Anti Tank
High Explosive, Anti-Tank (HEAT) was a type of ammunition made of an explosive shaped charge that used the Neumann effect (a development of the Munroe effect) to create a very high-velocity jet of metal in a state of superplasticity that could penetrate through solid armour.
High Explosive Anti-Tank ammunition was first used in the Second World War; while some Canadian weapons utilized this ammunition (notably the Projector, Infantry, Anti-Tank, a variety of German weapons also employed this ammunition to great effect, notably the array of hand-held anti-tank weapons employed by German infantry units after 1943.
The principle of the HEAT shell is to direct a high-velocity jet of molten metal through solid armour, using the "Neumann effect". This jet is created when the round impacts the target; the kinetic energy of the blast is funneled through the narrow nose of the round, moving at hypersonic speeds and disintegrating the material in its path. (While effective during the Second World War on plate armour, reactive and ceramic armour types used in the latter half of the 20th Century and into the 21st have been designed to lessen the effects of HEAT).
The penetrating effect of the round also dissipates very rapidly, which is why German tanks often mounted armoured side skirts in the latter stage of the war - in order to detonate HEAT rounds before they could contact the main armour of the tank itself.
The first HEAT weapons were spurred by Swiss inventors who exhibited weapons before the Second World War based on the "shaped charge" principle.
The first HEAT warhead used by Canadians was the British No. 68 Grenade, a rifle grenade. It was followed by more effective combinations of warhead and delivery systems - the US "Bazooka" was a rocket-launching design (adopted by Canada after the Second World War), and the PIAT. The Germans also manufactured many rocket-launched HEAT weapons after capturing US bazookas in North Africa. These weapons all had a short range and were not the preferred method of combating enemy armour.
The need for a large bore made HEAT rounds relatively ineffective in small-caliber anti-tank guns, and the Recoilless Gun was developed during the Second World War. Canada began using these recoilless weapons after the Second World War.
The very real vulnerability to HEAT rounds of armour during the Second World War was a large concern to the world's militaries, and dramatic changes in the way armour was produced occurred after the Second World War, with the effect of making reducing the usefulness of HEAT by making the needed warhead so large as to be non-portable by infantry. The Carl Gustav 84mm rocket launcher remained on inventory of the Canadian Army for the last decades of the 20th Century, though the HEAT ammunition for that weapon became more and more obsolete to the task of dealing with the current state of the art in main battle tank armour.