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Basic Information

HEAT1 rounds are a form of shaped charge round which relies entirely on the Munroe Effect to penetrate armour.

The shaped charge was developed for use in mining, but arrived when the only explosive available was black powder which, not being a highexplosive was unable to make them work properly. Munroe (of the eponymous effect) then rediscovered the phenomenon by accident when he noticed that slabs of guncotton with the maker's name stamped into them would, in turn, stamp it into a steel plate when detonated in contact with it. Various attempts were made to turn it into a weapon, with the first theoretical patents being issued to a Swiss named Mohaupt in the late 1930s, but these were quickly bypassed and the first confirmed combat use was of man-portable HEAT demolition charges during the German assault on Eben Emael2. The Germans then developed the concept further by deploying a 75mm shell for the low velocity guns mounted on the early models of the PzKpfW IV and the StuG III. Everyone else then followed suit.

Essentially the payload charge is formed with an indentation in the front which creates a focused blast wave which the punches into the target - penetration depth varies on with the geometry of the round and various other factors but varies from 1.5-2x calibre in the earliest and most primitive designes to an alleged 7 calibres in the best modern ones.

HEAT allows decent armour penetration from a low velocity weapon and generally requires little in the way of special resources (unlike, say APDS shells). Also, as a (basically) explosive round it has a rather less limited effect against soft targets than many kinetic armour piercing designs (which tend to go in one side and out the other). That said, it has its drawbacks as well - firstly it doesn't like spin-stabilisation (which tends to upset the blast jet) and therefore is happier not being fired from rifled barrels, which can lead to a loss of accuracy. Also, the "HEAT jet" is prone to disruption from other angles - for example if it detonates too far away from the target the blast will dissapate before it has any effecy, and if it detonates too close the jet won't form properly. Hence the utility of mesh screens (or indeed old furniture) as applique tank armour. Early HEAT rounds were even prone to detonating on twigs and branches on their way to the target. As noted, a HEAT round's penetration is proportional to its diameter - which tends to militate towards larger bore guns (a nuisance in itself) but lead to more air-drag and a consquent loss of range and accuracy over distance.
HEAT is also most effective against homogenous armour - where the target's armour is instead composed of layers of unlike materials (for example in the British Chobham concept) performance is significantly degraded. Despite these apparently significant drawbacks, HEAT remains the technology of choice for most low velocity anti tank weapons, especially those built on a recoiless platform.


1. full source reference

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