M2 4.2 inch mortar

M2 4.2-Inch Mortar
A 4.2 inch mortar in Korea, 1952.
Type	Mortar
Place of origin	United States
Service history
In service	1943–1974 (United States) 1943-Present (Other nations)
Used by	U.S. Army U.S. Marine Corps
Wars	World War II Korean War
Specifications
Weight	151 kg (332.89 lbs)
Barrel length	overall: 1.22 m (4 ft)
Caliber	107 mm (4.2 in)
Rate of fire	5 rpm for 20 minutes 1 rpm indefinitely
Effective firing range	515 m (563.21 yd)
Maximum firing range	4,023 m (4,400 yd)

1943–1974 (United States)

The M2 4.2 inch Mortar was a U.S. rifled 4.2-inch (107 mm) mortar used during the Second World War and the Korean War. It entered service in 1943. It was nicknamed the "Goon Gun" (from its large bullet-shaped shells, monopod, and rifled bore - like a rifle for shooting Goons) or the "Four-Deuce" (from its bore size in inches). In 1951 it began to be phased out in favor of the M30 mortar of the same caliber.

The first 4.2-inch mortar in U.S. service was introduced in 1928 and was designated the M1 Chemical Mortar. Development began in 1924 from the British 4-inch (102 mm) Mk I smooth-bore mortar. The addition of rifling increased the caliber to 4.2-inch. The M1 fired chemical shells to a range of 2,400 yards (2,200 m). It was meant to fire smoke shells, as the postwar peace lobby opposed military spending on explosive or poison gas shells.

The M2 could be disassembled into a three parts to allow it to be carried by its crew. The mortar tube weighed 105 pounds (48 kg), including a screw-in cap at the bottom. The cap contained a built-in fixed firing pin. The standard, a recoiling hydraulic monopod that could be adjusted for elevation, weighed 53 pounds (24 kg). The baseplate had long handles on either side to make it easier to carry; it weighed 175 pounds (79 kg).

Upon the entry of the United States into World War II, the U.S. Army decided to develop a high explosive round for the mortar so that it could be used in a fragmentation role against enemy personnel. In order to extend the range to 3,200 yards (2,900 m), more propellant charge was used and parts of the mortar were strengthened. Eventually, the range of the mortar was extended to 4,400 yards (4,000 m). The modified mortar was redesignated the M2. The M2 was first used in the Sicilian Campaign, where some 35,000 rounds of ammunition were fired from the new weapon. Subsequently, the mortar proved to be an especially useful weapon in areas of rough terrain such as mountains and jungle, into which artillery pieces could not be moved. The M2 was gradually replaced in U.S. service from 1951 by the M30 mortar.

Starting in December 1942, the US Army experimented with self-propelled 4.2-inch mortar carriers. Two pilot vehicles based on the M3A1 halftrack were built, designated 4.2-inch Mortar Carriers T21 and T21E1. The program was cancelled in 1945.