Replacing the M27 recoilless rifle, the M40 primarily saw action during the Vietnam War and was widely used during various conflicts thereafter in Africa or in the Middle East. It was replaced by the BGM-71 TOW anti-tank missile system in the US armed forces.
The earlier M27 recoilless rifle was a 105-mm weapon developed in the early 1950s and fielded in the Korean War. Although a recoilless rifle of this caliber had been a concept since the Second World War, the weapon was hurriedly produced with the onset of the Korean War. The speed with which it was developed and fielded resulted in problems with reliability caused by trunnions that were mounted too far to the rear. The M27 was also considered too heavy by the U.S. Army and had a disappointing effective range due to the lack of a spotting rifle. Taking the M27 as the basis for a new design, the Army developed an improved version of the M27 that was type-designated the M40 106-mm recoilless rifle in 1955.[22] Although unsuitable for military purposes, M27 recoilless rifles were used to trigger controlled avalanches at ski resorts and mountain passes in the United States.[23]
Description
The M40 is shaped like a long tube with an M8C .50 cal spotting rifle above. The spotting rifle fires a round whose trajectory closely matches that of the 105 mm round and gives off a puff of smoke on impact with the target. On the left side, there is an elevating wheel, in the center of which is the trigger wheel used to fine adjust the elevation and at the same time firing the spotting rifle when pulled, and the gun when pushed. The mounting is a tripod, but the front leg has a castering wheel. On top of the mount is a traverse wheel. On the center of the traverse wheel is a locking wheel, when the wheel is down, the rifle is locked in traverse, and can only be moved right and left with the traverse wheel. When the wheel is raised, the rifle can be traversed by hand. Austria produced a two-wheeled mount for the M40.
A special vehicle called the Ontos carried six M40s. A version specific to the T195E5 mount, the M40A1C, was used. It was used only by the U.S. Marine Corps. Japan produced a self-propelled gun called the Type 60, which carried two side by side. Some Pakistani M113s have a dual mounting.[citation needed] Three Panagopoulos coastal patrol boats class of the Hellenic Coast Guard and the Hellenic Navy in service of 1976-2003 was armed with two sextuples M40.[29]
Ammunition for the 105 mm rifle was issued as one-piece fixed cartridges. The term "fixed" means that the projectile and the cartridge case are crimped together. This ensures correct alignment of the projectile and the cartridge case. It also permits faster loading because the projectile and the cartridge case are loaded as one unit. The rear end of the cartridge case is perforated, to allow the propellant gas to escape through the vented breech, thus neutralizing recoil. Most projectiles (except HEAT) used are pre-engraved, that is, the rotating bands are cut to engage the rifled bore.[36] If the round was not rotated slightly when loading the M40 it could result in jamming in the breech.
Types of ammunition included HEAT, High Explosive Plastic-Tracer (HEP-T), canister, High Explosive Anti Personnel, and the M368 dummy round which could not be fired and was used for crew drill. The original U.S. HEAT round penetrated more than 400 mm of armor. Near the end of the M40's service life, both Austria and Sweden produced HEAT rounds for the weapon capable of penetrating more than 700 mm of armor.[37]
The ammunition for the M8C spotting rifle is not .50 BMG, but a round often referred to as .50 BAT (Battalion Anti Tank), which is 12.7x77mm. .50 BAT was developed to replicate the trajectory of the 106 mm ammunition, and features a tracer element and a point-detonating incendiary filler to create a puff of smoke at the impact point.
Although the spotting rifle could conceivably be used in an antipersonnel role, historic U.S. military doctrine strongly discouraged this use, for a purely tactical reason—to conceal the vulnerable M40 and its crew from the enemy until the main rifle was ready to fire. However, this restriction is believed to be the source of a long-standing misconception that the laws of war restrict the use of .50-caliber projectiles against enemy personnel more generally.[44]
Civilian use
In the early 1990s, the United States Forest Service (USFS) introduced the M40 for avalanche control as ammunition stocks for their M27 rifles became depleted. The M40 was initially successful due to operational similarities to the familiar M27 and ready availability from the U.S. military; however, in 1995, a USFS gunner was killed by shrapnel after a low-level premature warhead detonation inside an M40 barrel. The accident was attributed to an undiscovered hairline crack in the projectile's base plate. Following this incident, most USFS M40s were quickly replaced with surplus 105 mm howitzers, but a few were kept in service with safety barriers to protect the gunners, who fired the guns remotely. In December 2002, two M40s at Mammoth Mountain were destroyed by catastrophic bore explosions 13 days apart. The gunners were uninjured, having been protected by the safety barriers, but the incidents prompted the USFS to retire all remaining M40s in July 2003.[45]
Myanmar: more than 1,000 M40A1 RCLs in service as of 2016[update],[95] including Pakistani-made M40A1s.[33] used for bunker busting and anti-personnel/infantry support role in counter-insurgency campaigns.
Switzerland:[115] In the period 1958–1990, the antitank companies of the Swiss Army Infantry Regiments were equipped with 12 M40 guns.[citation needed]
^Gander, Terry J. (15 March 1992). "RAT 700 106 mm projectile". Jane's Infantry Weapons 1992-1993.
^Gander, Terry J. (27 April 1994). "106 mm 3.1 RAT 700 HEAT-T projectile". Jane's Infantry Weapons 1994-1995.
^Parks, Maj W. Hays (January 1988). "Killing A Myth". Marine Corps Gazette. Archived from the original on 28 February 2014. Retrieved 20 February 2014.
^"Projectile – 106mm recoilless rifle"(PDF). defence.gov.au. Defence unexploded ordnance website: ordnance information sheet. March 2015. Archived(PDF) from the original on 2019-04-11. Retrieved 2018-11-06.
^ abcdefWiener, Friedrich (1987). The armies of the NATO nations: Organization, concept of war, weapons and equipment. Truppendienst Handbooks Volume 3. Vienna: Herold Publishers. p. 484.
^Gander, Terry J. (22 November 2000). "National inventories, Canada". Jane's Infantry Weapons 2001-2002.