High - explosive anti - tank warhead High - explosive anti - tank ( HEAT ) warheads are made of an explosive shaped charge that uses the Munroe effect to create a very high - velocity partial stream of metal in a state of superplasticity that can punch through solid armor . Contrary to a widespread misconception perpetuated by the acronym , HEAT rounds do not depend in any way on thermal phenomena for their effectiveness . In particular , the shaped charge jets do not " melt their way " through armor , only reaching 500 - 600 °C , and instead rely on extreme pressure to force a hole through the armor . Operation . The stream moves at hypersonic speeds ( up to 25 times the speed of sound ) in solid material and therefore erodes exclusively in the contact area of jet and armor material . The correct detonation point of the warhead and spacing is critical for optimum penetration , for two reasons : The key to the effectiveness of a HEAT round is the diameter of the warhead . As the penetration continues through the armor , the width of the hole decreases leading to a characteristic " fist to finger " penetration , where the size of the eventual " finger " is based on the size of the original " fist " . In general , very early HEAT rounds could expect to penetrate armor of 150 % to 250 % of their diameter , and these numbers were typical of early weapons used during World War II . Since the Second World War , the penetration of HEAT rounds relative to projectile diameters has steadily increased as a result of improved liner material and metal jet performance . Some modern examples claim numbers as high as 700 % . HEAT projectile stabilization and accuracy . HEAT warheads become much less effective if they are rapidly spinning , which became a challenge for weapon designers – for a long time , spinning the shell was the most standard method for obtaining good accuracy , as with any rifled gun . However , the centrifugal force of a spinning shell disperses the charge jet . Consequently , most hollow charge projectiles are fin - stabilized and not spin - stabilized . The round could be fired from smoothbore barrel , losing some accuracy . In recent years it has become possible to use shaped charges in spin - stabilised projectiles by imparting an opposite spin on the jet so that the two spins cancel out and result in a non - spinning jet . This is done either using fluted copper liners , which have raised ridges or by manufacturing the liner in such a way that it has a crystalline structure which itself imparts a spin on the jet . Besides spin - stabilisation , another problem with any barreled weapon ( that is , a gun ) is that large - diameter shell has worse accuracy than small - diameter shell of the same weight . The lessening of accuracy increases dramatically with range . Paradoxically , this leads to situation when a kinetic armor - piercing projectile is " more " usable at long ranges than a HEAT projectile , despite the latter having a " higher " armor penetration . To illustrate this : a stationary Soviet T - 62 tank , firing from ( smoothbore ) cannon at a range of 1000 meters against a target moving 19 km / h , was rated to have a first - round hit probability of 70 % when firing a kinetic ( APFSDS ) projectile . Under the same conditions , it could expect 25 % when firing HEAT round . This affects combat on open battlefield with long lines of sight ; the same T - 62 could expect a 70 % first - round hit probability using HEAT rounds on target at 500 meters . A further problem is that , if the warhead is contained inside the barrel , its diameter becomes overly restricted by the caliber of that barrel . In non - gun applications , when HEAT warhead is delivered with missile s , rocket s , bomb s , grenade s , or spigot mortars , the warhead size is no longer a limiting factor . In these cases HEAT warhead often seems oversized in relation to the round ' s body . Classic examples of this include the German Panzerfaust and Soviet RPG - 7 . History . Shaped charge warheads were promoted internationally by the Swiss inventor Henry Mohaupt , who exhibited the weapon before the Second World War . Prior to 1939 Mohaupt had demonstrated his invention to British and French ordnance authorities . During the war the French communicated the technology to the U . S . Ordnance Department , who recognized the significance of Mohaupt ' s research and invited him to the U . S . A . He arrived there in October 1940 to work as a consultant on the Bazooka project , one of the first applications of the shaped charge . Independent secret development by the German group of Cranz , Schardin , and Thomanek led to the first documented use of shaped charges in warfare , in a successful assault on the fortress of Eben Emael on 10 May 1940 . Claims for priority of invention are difficult to resolve due to subsequent historic interpretations , secrecy , espionage , and international commercial interest . It is not even certain the German and Swiss groups were truly independent . By mid - 1940 Germany introduced the first HEAT round to be fired by a gun , the 7 . 5 cm fired by the Kw . K . 37 L / 24 of the Panzer IV tank and the Stug III self - propelled gun ( 7 . 5 cm Gr . 38 Hl / A , later editions B and C ) . In mid - 1941 Germany started the production of HEAT rifle - grenades , first issued to paratrooper s and by 1942 to the regular army units ( " Gewehr - Panzergranate 40 " , " 46 " and " 61 " ) , but as with the British soon turned to the integrated warhead - delivery systems : In 1943 the " Püppchen " , " Panzerschreck " and " Panzerfaust " were introduced . The Panzerfaust and Panzerschreck or ' tank terror ' gave the German infantryman the ability to destroy any tank on the battlefield from 50 - 150m with relative ease of use and training ( unlike the UK PIAT ) . The Germans also made use of large quantities of HEAT ammunition in converted 7 . 5 cm Pak 97 / 38 guns from 1941 , later fabricating a HEAT warhead for the " Mistel " weapon . The latter weighed nearly two tons and was perhaps the largest HEAT warhead ever deployed . It was intended for use against heavily armoured warships , like battleships . During World War II the British referred to the Monroe effect as the cavity effect on explosives . The first British HEAT weapon to be developed and issue was a rifle grenade using a 2 1 / 2 inch cup launcher on the end of the barrel ; the British No . 68 AT grenade issued to the British army in 1940 . By 1943 the combination of HEAT warhead and spigot mortar delivery in the cumbersome PIAT weapon at last allowed British infantry to engage armour at ranges not bordering on suicide , about 115 yards ; as was sometimes the case with magnetic hand - mines and grenades . The Germans came up with an effective counter to hollow - charged or HEAT weapons such as the PIAT or Bazooka through the use of armoured skirts or mesh skirts on their tanks , which caused the HEAT shell to detonate prematurely . The need for a large bore made HEAT rounds relatively ineffective in existing small - caliber anti - tank guns of the era . The Germans were able to capitalize on this , however , introducing a round that was placed over the end on the outside of their otherwise obsolete 37 mm anti - tank guns to produce a medium - range low - velocity weapon . Adaptations to existing tank guns were somewhat more difficult , although all major forces had done so by the end of the war . Since velocity has little effect on the armor - piercing capability of the round , which is defined by explosive power , HEAT rounds were particularly useful in long - range combat where the slower terminal velocities were not an issue . The Germans were again the ones to produce the most capable gun - fired HEAT rounds , using a driving band on bearings to allow it to fly unspun from their existing rifled tank guns . HEAT was particularly useful to them because it allowed the low - velocity large - bore guns used on their numerous assault gun s to become useful anti - tank weapons as well . Likewise , the Germans , Italians , and Japanese had many obsolescent " infantry guns " in service ( short - barreled , low - velocity artillery pieces capable of both direct and indirect fire and intended for infantry support , similar in tactical role to mortars ; generally an infantry battalion had a battery of four or six ) . HEAT rounds for these old infantry guns made them semi - useful anti - tank guns , particularly the German 150 mm guns ( the Japanese 70 mm and Italian 65 mm infantry guns also had HEAT rounds available for them by 1944 but they were not very effective ) . The general public remained in the dark about shape charge warheads ( i . e . they even believed that it was a new super secret explosive ) until early 1945 when the US Army co - operated with the US monthly publication " Popular Science " on a large and detailed article on the subject . Most Americans were shocked to learn that even their enemies in World War II had what the US Army referred to as shape charge warhead weapons . During World War II , weapons using HEAT warheads were known as having a hollow charge or shape charge warhead . HEAT rounds caused a revolution in anti - tank warfare when they were first introduced in the later stages of World War II . A single infantryman could effectively destroy any existing tank with a handheld weapon , thereby dramatically altering the nature of mobile operations . After the war HEAT became almost universal as the primary anti - tank weapon . HEAT rounds of varying effectiveness were produced for almost all weapons from infantry weapons like rifle grenade s and the M203 grenade launcher , to larger dedicated anti - tank systems like the Carl Gustav recoilless rifle . When combined with the wire - guided missile , infantry weapons were able to operate in the long - range role as well . Anti - tank missiles altered the nature of tank warfare throughout the 1960s and into the 80s , and remain an effective system today . Helicopter armament . Helicopters have also carried anti - tank guided missiles ( ATGM ) tipped with HEAT warheads since the early 1960s . The first example of this was the use of the Nord SS . 11 ATGM on the Aérospatiale Alouette II helicopter by the French armed forces . Subsequently , such antitank - capable helicopters were widely adopted by other nations . On April 13 , 1972 , Chief Warrant Officer Barry McIntyre , Major Larry McKay , First Lieutenant Steve Shields , and Captain Bill Causey became the first helicopter crews to destroy enemy armour in combat during the Vietnam War . A flight of two Cobra helicopters from Battery F , 79th Artillery , 1st Cavalry Division , U . S . Army , were armed with the newly developed 2 . 75 " HEAT rockets , which were yet untested in combat . The specially modified Huey which was shipped in an emergency destroyed three T - 54 tank s that were about to overrun a U . S . command post . McIntyre and McKay engaged first , destroying the lead tank . Armor developments . Improvements to the armor of main battle tank s have reduced the usefulness of HEAT warheads by making man portable HEAT missiles heavier , although many of the world ' s armies continue to carry man portable HEAT rocket launchers for use against vehicles and bunkers . In unusual cases , shoulder - launched HEAT rockets are believed to have shot down U . S . helicopters in Iraq . The reason for the ineffectiveness of HEAT munitions against modern main battle tanks can be attributed in part to the use of new types of armor . The jet created by the explosion of the HEAT round must have a certain distance from the target and must not be deflected . Reactive armor attempts to defeat this with an outward directed explosion under the impact point , causing the jet to deform and so greatly reducing penetration power . Alternatively , composite armor featuring ceramic s erode the liner jet more quickly than rolled homogeneous armor steel , the then - preferred material in the construction of armored fighting vehicle s . Spaced armor and slat armor are also designed to defend against HEAT rounds , protecting the vehicle by causing a premature detonation of the explosive at a relatively safe distance away from the main armor of the vehicle . Variations . Many HEAT - armed missiles today have two ( or more ) separate warheads ( known as a tandem charge ) to be more effective against reactive or multilayered armor ; the first , smaller warhead initiates the reactive armor , while the second ( or other ) , larger warhead penetrates the armor below . This approach requires highly sophisticated fuzing electronics to set off the two warheads the correct time apart , and also special barriers between the warheads to stop unwanted interactions ; this makes them more expensive to produce . The latest HEAT warheads , such as 3BK - 31 , feature triple charge , where the first one penetrates the spaced armor , the second - reactive or first layers of armor , and the third one finishes the penetration . The total penetration value may reach up to 800 mm . Some anti - armor weapons incorporate a variant on the shaped charge concept that , depending on the source , can be called an Explosively Formed Penetrator ( EFP ) , Self Forging Fragment ( SFF ) , SElf FOrging Projectile ( SEFOP ) , plate charge , or Misznay Schardin ( MS ) charge . This warhead type uses the interaction of the detonation wave ( s ) , and to a lesser extent the propulsive effect of the detonation products , to deform a dish / plate of metal ( iron , tantalum , etc . ) into a slug - shaped projectile of low length to diameter ratio ( L to D ) and project this towards the target at around two kilometres per second . The SFF is relatively unaffected by first generation reactive armor , it can also travel up to , and above 1000 cone diameters ( CDs ) before its velocity becomes ineffective at penetrating armor due to aerodynamic drag , or hitting the target becomes a problem . The impact of a SFF normally causes a large diameter , but relatively shallow hole ( in comparison to a shaped charge ) of , at best , a few CDs . If the SFF perforates the armor , extensive behind armor damage ( BAD , also called behind armor effect ( BAE ) ) occurs . The BAD is mainly caused by the high temperature and velocity armor and slug fragments being injected into the interior space and also overpressure ( blast ) caused by the impact . More modern SFF warhead versions , through the use of advanced initiation modes , can also produce rods ( stretched slugs ) , multi - slugs and finned projectiles , and this in addition to the standard short L to D ratio projectile . The stretched slugs are able to penetrate a much greater depth of armor , at some loss to BAD , multi - slugs are better at defeating light and / or area targets and the finned projectiles have greatly enhanced accuracy . The use of this warhead type is mainly restricted to lightly armored areas of MBTs — the top , belly and rear armored areas for example . It is well suited for use in the attack of other less heavily armored armored fighting vehicles ( AFVs ) and in the breaching of material targets ( buildings , bunkers , bridge supports , etc . ) . The newer rod projectiles may be effective against the more heavily armored areas of MBTs . Weapons using the SEFOP principle have already been used in combat ; the smart submunitions in the CBU - 97 cluster bomb used by the US Air Force and US Navy in the 2003 Iraq war used this principle , and the US Army is reportedly experimenting with precision - guided artillery shells under Project SADARM ( Seek And Destroy ARMor ) . There are also various other projectile ( BONUS , DM 642 ) and rocket submunitions ( Motiv - 3M , DM 642 ) and mines ( MIFF , TMRP - 6 ) that use SFF principle . With the effectiveness of gun - fired single charge HEAT rounds being lessened , or even negated by the increasingly sophisticated armoring techniques , a class of HEAT rounds known as high - explosive anti - tank multi - purpose , or HEAT - MP , has become more popular . These are essentially HEAT rounds which are effective against older tanks and other armored vehicles , but have improved fragmentation , blast and fuzing . This gives the projectiles an overall reasonable light armor and anti - personnel / materiel effect so that they can be used in place of conventional high - explosive rounds against infantry and other battlefield targets . This reduces the total number of rounds that need to be carried for different roles , which is particularly important for modern tanks like the M1 Abrams , due to the sheer size of 120 mm rounds used . The M1A1 / M1A2 tank can carry only 40 rounds for its 120 mm M256 gun — the M60A3 Patton tank ( the Abrams ' predecessor ) , carried 63 rounds for its 105 mm M68 gun . This effect is reduced by the higher first round hit rate of the Abrams with its improved fire control system compared to the M60 . The frequent fuel replenishments required for the Abrams ' fuel - hungry turbine also make simultaneous ordnance replenishment a marginal burden . High - explosive dual purpose . Another variation on HEAT warheads is surrounding them with a conventional fragmentation casing , to allow the warhead to be more effectively used for blast and fragmentation attacks on unarmored targets . In some cases this is merely a side effect of the armor - piercing design , in other cases a dual role is specifically designed in . Some warheads have been known as HEDP — high - explosive dual purpose .