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 . History . 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 . Burning 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 : spall ing 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 . 4mm . 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 . Other examples became evident during the Vietnam War . The North Vietnamese and their allied forces in South Vietnam were equipped with two types of light anti - armour weapons . One was the 1950s era B - 40 , which was a Chinese manufactured version of the Russian RPG - 2 , and the other was the newer RPG - 7 . The RPG - 2 had a shallow cone and the RPG - 7 a deep cone . The B - 40 had a maximum penetration against armour of approximately 150mm while the RPG - 7 penetration was more than double that of the B - 40 . But to the surprise of the North Vietnamese , the B - 40 , while not effective against heavy tanks , was far more effective than the RPG - 7 in killing or wounding the occupants of light armoured vehicles , and in igniting the ammunition storage or the vehicle ' s fuel , including the more modern M113 APC which U . S . and South Vietnamese forces at that time operated in large numbers . In addition , the B - 40 proved more effective than the RPG - 7 against non - armoured targets , like the bunkers at fire base camps . There are many stories from U . S . Vietnam veterans of the enemy attacking or ambushing with the dreaded B - 40 . The U . S . Army also discovered that in combat , with rare exceptions , more than one hit by the M72 LAW rocket was required to disable or kill the North Vietnamese PT - 76 light tank . Development . The combat record of light anti - armour weapons was studied by the engineers at FFV working on a replacement for the Pansarskott m / 68 in the late 1970s . The result was the AT4 with a HEAT warhead that had , as the early AT4 brochures stated , a " special beyond - armour effect " . The designers of the AT4 ' s warhead intended that one hit would cause massive damage to the both the occupants and the interior of the targeted vehicle . FFV has said very little about the design of the AT4 ' s warhead , being willing only to describe its effects . Defense journalists and military experts have speculated on the warhead ' s design . A cutaway photo of the AT4 ' s projectile gave clues . Instead of the standard cone shape liner used by other HEAT warheads , the AT4 has a unique trumpet - shaped liner . Trumpet - shaped liners are believed to be more effective in resisting the counter - blast of reactive armour tiles , that explode and disrupt the HEAT warhead ' s particle stream . There has been speculation that the liner in the AT4 ' s HEAT warhead is constructed of a special aluminum alloy . Others have stated it is primarily a copper liner with a secondary liner of aluminum bonded to the back of the copper liner . Another clue to the effectiveness of the AT4 is the presence of a " focus ring " to concentrate the blast . All public statements to date on the subject are speculative . Tests conducted by the U . S . Army on the AT4 confirmed that the claims made by FFV regarding the AT4 ' s devastating post - penetration effect were substantially correct . Description . As described by FFV in their first AT4 brochure in 1983 , the " beyond - armour effect " had five distinctive characteristics upon penetration of an armoured vehicle : FFV claims that besides the effect of the massive spalling and fragmentation on the occupants of the armoured vehicle , which is standard for all HEAT warheads to a degree , the massive overpressure and intense heat will cause ammunition and more importantly the armoured vehicle ' s diesel fuel to ignite . The intense light effect will blind any occupants for at least seven minutes , in addition to the obscuring effect of the dense smoke created by the AT4 ' s HEAT warhead .