The M40 recoilless rifle is a portable, crew-served 105 mm recoilless rifle made in the United States. Intended primarily as an anti-tank weapon, it could also be employed in an antipersonnel role with the use of an antipersonnel-tracer flechette round. The bore was commonly described as being 106 mm caliber but is in fact 105 mm; the 106 mm designation was intended to prevent confusion with incompatible 105 mm ammunition from the failed M27. The air-cooled, breech-loaded, single-shot rifle fired fixed ammunition and was used primarily from a wheeled ground mount. It was designed for direct firing only, and sighting equipment for this purpose was furnished with each weapon, including an affixed spotting rifle.
A deactivated M40 on display at the Philippine Army Museum
Ontos M50A1 with six 105 mm M40 recoilless rifles
Jonga, mounted with 105 mm RCL gun which destroyed most of the tanks during the 1965 and 1971 Indo-Pakistani wars
Greek Mercedes 240G M40 carrier. Note the metal guard to protect the engine from the gun blast.
A recoilless rifle (rifled), recoilless launcher (smoothbore), or simply recoilless gun, sometimes abbreviated to "RR" or "RCL" is a type of lightweight artillery system or man-portable launcher that is designed to eject some form of countermass such as propellant gas from the rear of the weapon at the moment of firing, creating forward thrust that counteracts most of the weapon's recoil. This allows for the elimination of much of the heavy and bulky recoil-counteracting equipment of a conventional cannon as well as a thinner-walled barrel, and thus the launch of a relatively large projectile from a platform that would not be capable of handling the weight or recoil of a conventional gun of the same size. Technically, only devices that use spin-stabilized projectiles fired from a rifled barrel are recoilless rifles, while smoothbore variants are recoilless guns. This distinction is often lost, and both are often called recoilless rifles.
An M40 recoilless rifle on its M79 "wheelbarrow" tripod
Jonga, mounted with 105 mm RCL gun which destroyed most of the tanks during the 1971 Indo-Pakistani war
1.57-inch Davis recoilless gun mounted in the nose of an F5L flying boat, with a parallel Lewis machine gun. Photo circa 1918.
M67 recoilless rifle