High Explosive Anti-Tank (or in short HEAT) ammunition refers to shaped charge warheads, that are in use since the Second World War. They can take many shapes and sizes, ranging from rifle grenades to rockets. The way they work is rather specific and there are a lot of misconceptions out there, so hopefully this article will help to defuse this topic.
How do shaped charges work?
The heart of every shaped charge is the conical liner, which basically means a hollow cone shape, usually made out of metal (typically copper). This is combined with high explosives, so the hollow end of the cone points towards the target. Upon explosion, due to the massive forces the cone shape collapses on itself, and a part of it forms a stream of concentrated particles called the jet. Contrary to popular belief the jet is not a super hot liquid that burns its way through armor, but is instead solid material moving at hyper-sonic speed, that pushes the opposing material simply out of its way (thus the damage done is of kinetic nature).
Specialties of HEAT ammunition
- The detonation has to occur just at a right distance from the target. Too close, and it won’t have enough time to fully develop the jet. Too far, and it disperses before it has reached its full potential (typically the stream disintegrates well under 2 meters).
- The effectiveness of HEAT ammunition depends largely on the diameter of the original warhead, and thus the liner. As the jet passes through the armor, the diameter of the hole decreases, so naturally a larger original diameter means that the hole created will decrease to zero over a longer distance. Older charges could penetrate armor up to 150 to 250% of their diameter, while modern charges in comparison can go up to 700%.
- Velocity has little effect on the armor piercing capability of HEAT rounds, thus they are very helpful for long-range engagements.
- HEAT shells get less effective the faster the shells spin, as the centrifugal force disperses the jet. This is a problem as most guns use rifled barrels to improve accuracy. The solution is to use smooth bore barrels losing some accuracy, or to use special spin-stabilized projectiles, where the shell itself spins, but the jet doesn’t.
Defense against HEAT ammunition
The modern main battle tanks can use two high-tech solutions to fight the threat that HEAT ammunition poses to them: composite armor or reactive armor. Composite armor introduces ceramics to the armor plating, which erodes the jet much faster than the traditional rolled homogeneous armor, thus drastically reducing its penetration potential. Reactive armor on the other hand fights HEAT with an outward directed explosion under the impact point, causing the jet to deform and disperse.
There are more traditional ways however as well – spaced armor is very effective against HEAT, because it exploits the limited range of the jet. By causing a premature explosion, the jet can disintegrate before going through the main armor of the vehicle. (The side and turret skirts fitted to some of the German tanks during World War II were originally there to protect against anti-tank rifles, but worked well against the early shaped charges as well.) In today’s battles however many HEAT warheads use multiple / tandem charges, to allow going through reactive and/or spaced armor as well.
Although the concept of shaped charges was publicized already by 1900, its potential remained unnoticed until the Second World War, when the German, British, Soviet and American forces all started to develop their own solutions. The very first HEAT weapon was most probably the British design No. 68 / AT rifle grenade, that could be fired from a cup launcher at the end of the rifle barrel, and that was issued to the British Armed Forces already by 1940.
By mid-1940 however the Germans already introduced the first HEAT shells for the 75mm gun of the Panzer IV and STUG III, while rolling out their own HEAT rifle-grenades in 1941. Two years later they also introduced the much feared Panzerfaust and Panzerschreck, handheld infantry anti-vehicle systems. These were extremely efficient at taking out any tank from 50 to 150 meters, while requiring minimal training only and being relatively easy to use. As an answer the British forces came up with the PIAT system, while America was working hard on their Bazooka project to have a handheld HEAT system of their own.
After the war, HEAT rounds became almost universal as the main anti-tank weapon, as they can be delivered by a multitude of solutions ranging from high caliber shells to rockets or guided missile systems. With the improved anti-HEAT armoring techniques, these days two main HEAT variants gained popularity: Tandem / multiple charges to fight reactive and spaced armor and multi-purpose HEAT shells. These have improved fragmentation, blast and fusing, while maintaining a reasonable penetration potential as well. These are now increasingly used instead of regular HE shells, to reduce the type of shells that need to be carried for the different possible roles.
It is worth to mention perhaps that shaped charges are not only used by the military, but also in mining, demolition, steel-making and by the petroleum- and gas industries.