M31 HEAT rifle grenade
Encyclopedia
The M31 HEAT is a fin-stabilized anti-tank rifle grenade
designed in the late 1950s to replace the Belgian ENERGA
rifle grenade which was adopted by the US Army and US Marines as an emergency stop-gap measure during the Korean War. Like the ENERGA, it has a nose-initiated, based-detonated HEAT
warhead, but unlike the ENERGA, the mechanical impact fuse system is replaced with a less complex and more reliable piezo-electric
fuze system which also allows higher angles of impact, up to 65 degrees. On impact, the nose cover collapses, crushing a crystal-like material, which sends an electric current through a separate wire to the warhead's detonator, located in the base of the warhead. A mechanical safety, comprising a set back system located in the warhead's base, grounds the firing circuit and prevents the accidental explosion of the warhead. On firing, the sudden launch acceleration causes the set-back's three disks to rotate 90 degrees, each in succession to the other, with the rotation of the third disk removing the grounding after approximately 10 meters of flight and completing a firing circuit for the current to flow from the nose to the detonator in the base. Compared to the ENERGA, the M31 is slightly lighter in weight and has a smaller-diameter warhead—ie 75mm vs 66mm. Penetration for the M31 is estimated to be 200 mm / 8 inches for steel armor plating and twice that estimate for concrete. The warhead technology developed for the M31 was used for the future M72 LAW
antitank rocket.
The M31 was originally designed to be fired only from the M1 Garand
, but was later adapted for the M14
rifle. To launch the M31, a detachable spigot-type grenade launcher (M7A3 launcher for M1 rifle, and M76 launcher for the M14 rifle) is fitted to the muzzle of the rifle. A M3 ballistic cartridge (two are supplied in the packing container with each grenade and are crimped to indicate the cartridges are only for launching rifle grenades) is loaded into the rifle's chamber. The hollow tail unit of the rifle grenade is fitted over the grenade launcher. Official military manuals recommend that the M31 HEAT be fired from either the standing or kneeling position and that it is only accurate against armored vehicles if fired at extremely close ranges. While claimed to be effective against both heavy tanks (except in frontal engagements) and lightly armored vehicles when first introduced, in 1972 the US Army stated in its revised anti-armor warfare manual that the M31 HEAT was only effective against light tanks and thin-skinned vehicles.
Various US military manuals issued in 1972 still had sections on the M31, but by the end of the Vietnam War, both the US Army and US Marines had essentially phased out muzzle-launched rifle grenades, in favor of the M72 LAW
disposable rocket in the anti-armor role and the M203
under-barrel grenade launcher in the squad fire-support role. In the 1977 revision of US military anti-armor warfare manuals, the M31 HEAT was no longer listed.
Rifle grenade
A rifle grenade is a grenade that uses a rifle-based launcher to permit a longer effective range than would be possible if the grenade was thrown by hand...
designed in the late 1950s to replace the Belgian ENERGA
ENERGA anti-tank rifle grenade
The Energa anti-tank rifle grenade is a rifle-launched anti-tank grenade that is propelled by a ballistite-filled blank cartridge. The name Energa comes from the firm in Liechtenstein that designed it, the Anstalt für die ENtwicklung von ERfindungen und Gewerblichen Anwendungen, based in...
rifle grenade which was adopted by the US Army and US Marines as an emergency stop-gap measure during the Korean War. Like the ENERGA, it has a nose-initiated, based-detonated HEAT
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
warhead, but unlike the ENERGA, the mechanical impact fuse system is replaced with a less complex and more reliable piezo-electric
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
fuze system which also allows higher angles of impact, up to 65 degrees. On impact, the nose cover collapses, crushing a crystal-like material, which sends an electric current through a separate wire to the warhead's detonator, located in the base of the warhead. A mechanical safety, comprising a set back system located in the warhead's base, grounds the firing circuit and prevents the accidental explosion of the warhead. On firing, the sudden launch acceleration causes the set-back's three disks to rotate 90 degrees, each in succession to the other, with the rotation of the third disk removing the grounding after approximately 10 meters of flight and completing a firing circuit for the current to flow from the nose to the detonator in the base. Compared to the ENERGA, the M31 is slightly lighter in weight and has a smaller-diameter warhead—ie 75mm vs 66mm. Penetration for the M31 is estimated to be 200 mm / 8 inches for steel armor plating and twice that estimate for concrete. The warhead technology developed for the M31 was used for the future M72 LAW
M72 LAW
The M72 LAW is a portable one-shot 66 mm unguided anti-tank weapon, designed in the United States by Paul V. Choate, Charles B. Weeks, and Frank A. Spinale et al...
antitank rocket.
The M31 was originally designed to be fired only from the M1 Garand
M1 Garand
The M1 Garand , was the first semi-automatic rifle to be generally issued to the infantry of any nation. Called "the greatest battle implement ever devised" by General George S...
, but was later adapted for the M14
M14 rifle
The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...
rifle. To launch the M31, a detachable spigot-type grenade launcher (M7A3 launcher for M1 rifle, and M76 launcher for the M14 rifle) is fitted to the muzzle of the rifle. A M3 ballistic cartridge (two are supplied in the packing container with each grenade and are crimped to indicate the cartridges are only for launching rifle grenades) is loaded into the rifle's chamber. The hollow tail unit of the rifle grenade is fitted over the grenade launcher. Official military manuals recommend that the M31 HEAT be fired from either the standing or kneeling position and that it is only accurate against armored vehicles if fired at extremely close ranges. While claimed to be effective against both heavy tanks (except in frontal engagements) and lightly armored vehicles when first introduced, in 1972 the US Army stated in its revised anti-armor warfare manual that the M31 HEAT was only effective against light tanks and thin-skinned vehicles.
Various US military manuals issued in 1972 still had sections on the M31, but by the end of the Vietnam War, both the US Army and US Marines had essentially phased out muzzle-launched rifle grenades, in favor of the M72 LAW
M72 LAW
The M72 LAW is a portable one-shot 66 mm unguided anti-tank weapon, designed in the United States by Paul V. Choate, Charles B. Weeks, and Frank A. Spinale et al...
disposable rocket in the anti-armor role and the M203
M203 grenade launcher
The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...
under-barrel grenade launcher in the squad fire-support role. In the 1977 revision of US military anti-armor warfare manuals, the M31 HEAT was no longer listed.