M2 mortar

M4 Collimator sight, used for both indirect fire and direct lay missions.

The U.S. M2 60 mm mortar was developed from the heavier 81 mm M1 Mortar to provide a lighter-weight alternative to company-level fire support.[1] The M2 attempted to bridge the gap between the 81 mm mortar and the hand grenade. Normally employed by the weapons platoon of a U.S. infantry company, the M2 is of the usual mortar pattern of the day.[1][2] It consists of a smoothbore metal tube on a rectangular baseplate, supported by a simple bipod with the elevation and traverse mechanisms. The firing pin was fixed in the base cap of the tube, and the bomb was fired automatically when it dropped down the barrel. Though classed as a light mortar, the M2 had considerable range compared to the 50 mm and 60 mm mortars of most other nations, and its fixed-firing pin design allowed a high rate of fire by trained crews.[1]

During the late 1920s, the US Army began examining mortars to act as a light infantry support weapon. The War Department eventually settled on a 60 mm design from Edgar Brandt, a French ordnance engineer, and purchased a license to build the weapon. The model was standardized as the Mortar, 60 mm M2. Testing took place in the late 1930s, and the first order for 1,500 M2 mortars was placed in January 1940.

The weapon was used throughout World War II by the U.S. Army and U.S. Marine Corps. It saw service again in the Korean War, and by French forces in counterinsurgency campaigns in Indochina and Algeria.[3] It was used under designation m/952 by Portugal during Portuguese Colonial War.[4] During the Vietnam War, the M2 was again used by the U.S. Army and Marines, as well as by South Vietnamese forces. Ultimately, the M2 was replaced by the M224 in 1978.

China (the Republic of China, prior to 1949) also locally produced the M2 mortar, which was designated as the Type 31.[5] Some were supplied to North Korea[6] and North Vietnam.[7] It was later modified as the Type 63[8] and then as the Type 63-1 mortar. This latter type has been produced under license by Pakistan Machine Tool Factory Limited in Pakistan and by Helwan Machine Tools Company in Egypt.[9]

Each mortar shell had a screw-on cap in its base. Inside the hollow in the tail, it contained a 20-gauge M5A1 Ignition Cartridge. This was a paper shotgun shell filled with ballistite powder.

The mortar had a firing pin in the bottom of the tube. When the shell was dropped down the tube, the firing pin struck the Ignition Cartridge in the shell's tail, detonating it. When the cartridge detonated, the explosive gases exited the base of the shell through two bleed holes. This propelled the shell out of the tube in an arc. Unassisted, the mortar shell had a range of about 200 to 325 yards.

To increase the mortar's range, shells were issued with four waterproof cellophane bags of propellant, called increments, fastened to the stabilizing fins with wire clips. The ignition cartridge would ignite the propellant, increasing chamber pressure and the shell's muzzle velocity. All four increments and the ignition cartridge pushed the maximum range to about 2,000 yards at 45 degrees elevation (depending on the shell's length and weight). To reduce the mortar's muzzle velocity, increment charges were removed as needed before firing. This allowed great flexibility in the angle at which shells impacted the target area, allowing the weapon to drop shells behind hills or buildings.

60mm mortar shells for the U.S. M2 Mortar. Left-to-Right: M69 Training/Practice, M49A2 High Explosive, M302 White Phosphorus/Smoke, M83 Illuminating (parachute flare)

U.S. Marines firing M2 mortar during the Korean War. August, 1952

The M2 Mortar could fire several types of ammunition.

• M49A2 High explosive (HE) with Point Detonating fuze M52B1 [Weight: 2.73 lbs]:[10] An explosive shell used against infantry and other light area targets. It has a minimum range of 200 yards when fired without a boosting charge at a 70° angle and a maximum range of 2017 yards when fired with four boosting charges at a 45° angle.
• M49A3 High Explosive Cartridge (HE) with Super-Quick Point Detonating fuze M525 [Weight: 3.05 lb (1.38 kg)]: Often referred to in the field as "HE quick".
• M302 White phosphorus Cartridge (WP): A "bursting smoke" shell used as a signaling, screening, smoke-producing, and casualty-producing shell.
  Unlike regular smoke shells of the period, which used a "hot" chemical reaction to generate a smoke cloud, the white phosphorus shell detonates to expose its filler to the air, causing it to spontaneously ignite and generate a thick cloud of white or grey smoke. It also sets combustible materials in its radius of effect on fire, causing secondary smoke sources. If personnel are hit by burning white phosphorus, the fragments will continue to burn inside the wound. They need to be evacuated to a hospital to have the fragments removed under special conditions.
• M83 Illuminating Cartridge (ILL): A pyrotechnic parachute flare shell used in night missions requiring illumination for assistance in observation.
• M69 Training/Practice Cartridge (TP) [Weight: 4.43 lb (2.01 kg)]: A shell with a cast iron body, inert filler, and detachable fin assembly used to train recruits in firing the M2 mortar. The cast iron body is reusable and the fin assembly can be replaced if damaged.
• M50A3 Training / Practice Cartridge (TP) [Weight 3.15 lb (1.43 kg)]: This practice shell is ballistically matched to the M49A4 HE shell, making it easier to train. They are the same size and weight, only differing in that the M50A3 is inert and emits a puff of white smoke on impact.

• List of U.S. Army weapons by supply catalog designation
• M1 mortar
• CM60A1

• Hogg, Ian (2000). Twentieth-Century Artillery. Friedman/Fairfax Publishers. ISBN 1-58663-299-X
• Norris, John and Calow, Robert, Infantry Mortars of World War II, Osprey Publishing (2002), ISBN 978-1-84176-414-6

• Cover photo of M2 60mm mortar May 1941 Popular Science