Beyond-armour effect
Beyond-Armour Effect is a term coined by Försvarets Fabriksverk (FFV), a semi-governmental Swedish defense firm, while developing the AT4. From the 1980s this phrase was used in its brochures, press releases, weapon instruction manuals and other documentation to denote the post-penetration effect of the AT4's HEAT anti-armour warhead against the interior and occupants of armoured vehicles.
The phrase now has become more or less standard in modern military terminology.
During World War II, man-portable antitank weapons using shaped charge warheads, more commonly known today as HEAT projectiles, came into widespread use with almost all armies. These warheads have the advantage of not being affected by the projectile's velocity. They penetrate armour by an explosive charge fitted in a liner in the shape of a cone or, more precisely, an ogive. The liner often is made of a soft metal, such as copper. Detonation of this shaped charge turns it into a highly focused stream moving forward at extreme speeds. These warheads also have the same effect as medium and high velocity solid shot armour piercing projectiles: spalling on the interior of the armoured vehicle's armoured plate.
A problem with shaped charge warheads is that if the ogive shaped liner is deep, it will have more penetration, that results in a smaller hole, that is less effective inside the armoured vehicle. Research on shaped charge warheads has shown a hole the size of a large coin on the outside of a tank turret, but an inside hole the diameter of pencil lead. If, on the other hand, the ogive is shallow, it will have less penetration, but cause a larger hole on the inside which will result in a massive spalling.
In 1954, during the siege of Dien Bien Phu, France had dismantled and flown in a number of M-24 Chaffee light tanks. Their thickest armor was only 25.4 mm. The Viet Minh's main infantry antitank weapon was the old World War Two U.S. 2.36-inch bazooka, captured from Nationalist Chinese forces and supplied by Communist China. During the siege the French launched counterattacks using the M-24 in support of their infantry. One Chaffee took seven hits from 2.36-inch bazookas and still continued to fight, demonstrating that portable rocket launchers were hardly a flawless tank-killer.
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