Introduced into service in 1943, the M2 107mm heavy mortar was a rifled mortar used by the United States during the World War II and the Korean War. It was nicknamed the “Four-Deuce,” as its bore size is 4.2 inches. The design of the M2 107mm mortar was based on the M1 chemical mortar and the British 4-inch Mk1 smoothbore mortar.

After the United States entered into World War II, the U.S. Army decided that it was necessary to develop a high-explosive round for the mortar so that it could be used as a fragmentation weapon against the enemy. More propellant charge was added and parts of the mortar were enhanced so that the effective range could be extended to 3,200 yards (2,900 meters). After the range of the mortar was extended even further to 4,400 yards (4,000 meters), the modified mortar was designated as the M2. It proved to be especially useful in areas of rough terrain, such as mountains or jungle areas, where artillery pieces typically could not venture.

The M2 107mm mortar could be disassembled into three separate parts, which allowed it to be carried by its crew. The mortar tube itself weighed 105 pounds, or 48 kilograms, including its screw-in cap, which contained a built-in fixed firing pin, at the base. The “standard,” a hydraulic recoiling monopod that could be adjusted for elevation, weighed in at 53 pounds (24 kilograms). With long handles on either side for easier carrying, the baseplate weighted in at 175 pounds (79 kilograms).

The rifled barreling of the M2 107mm mortar was somewhat unusual for a mortar, as its ammunition lacked the stabilizing tailfins that were common to most mortars. The mortar’s M3 HE (high-explosive) shell packed 3.64 kilograms of explosive charge, which placed it between the M1 105mm HE shell with 2.18 kilograms of charge and the M102 155mm HE shell with 6.88 kilograms of charge based on blast effect. The M2 could also fire mustard gas shells and white phosphorous-based smoke shells.