High explosive incendiary
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High Explosive Incendiary shells (HEIS) are shells is designed to penetrate the armour of the target using its high explosive properties, and then fragment and flare up, causing a fire either inside or outside of the target. HEI shells have been in use with numerous countries since the invention of the modern howitzer.
They work off the principle of a HEAT round, but are filled with flammable liquids to cause a secondary fire, which either detonates any combustible material such as ammunition or fuel and also injures crew, or simply causes large fires which must be dealt with. The incendiary capability also quickly depletes oxygen in small contained areas such as within a tank or shipboard compartment, causing suffocation of the crew.
[edit] Employment
The shells were first employed in naval batteries, but soon found their way to land-based howiters as well. They caused fires, which on ships can be difficult to extinguish in the tight spaces. Also, fired at tanks and soft targets, they can cause fires that completely engulf the vehicle, killing anyone inside.
Occasionally HEIS were used against tanks and other hightly armoured vehicles, but, since the invention of modern battle armour, such as Chobham, and Explosive Reactive Armour, these shells have become less and less practical for anti-tank work, and more useful for destroying “soft” targets such as airbases, trenches, or bunkers, in which they can create fires of over 1000 degrees Celsius. Incendiary shells are no longer in use by many countries, due to bans on the use of phosphorus weapons.
More common are APIS (Armour Piercing Incendiary Shells), these penetrate the target using the kinetic properties of the round, before the incendiary round goes off, smothering the crew in flames, and detonating ammunition, destroying the target.