High-explosive incendiary

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In warfare, High-explosive incendiary (HEI) is a type of ammunition specially designed to pierce armor, fragment, and ignite readily combustible materials.

HEI ammunition is fused either mechanically or chemically. The armor piercing ability can vary widely, allowing for more focused fragmentation or larger scatter. The incendiary capability also quickly depletes oxygen in small contained areas, such as within a tank or shipboard compartment, causing suffocation of crew.

[edit] Historical

HEI ammunition was originally developed for use in large-caliber cannon, howitzer and naval artillery. Currently, HEI rounds are most commonly made in medium-caliber sizes of 20 mm, 25 mm, and 30 mm. They are fired from various platforms, including aircraft, anti-aircraft cannons, and anti-missile systems, as well as common battlefield howitzers, though the latter has gone through a recent decline in use.

HEI ammunition has also been used on the battlefield against tanks and other armoured vehicles, but this has become impractical due to the invention of modern armour systems such as Chobham and explosive reactive armour, which can absorb most high-explosive rounds currently used.

Recently, APIS (armour piercing incendiary shells) have been used; these penetrate the target using the kinetic properties of the round before the incendiary round goes off, smothering the crew in flames and detonating combustible materials, generally destroying the target.