The 155 mm gun motor carriage M12 was a U.S.

self-propelled gun Self-propelled artillery (also called locomotive artillery) is artillery equipped with its own propulsion system to move toward its firing position. Within the terminology are the self-propelled gun, self-propelled howitzer, self-propelled mo ...

developed during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. It mounted a 155 mm gun derived from the French

Canon de 155 mm GPF The Canon de 155 Grande Puissance Filloux (GPF) modèle 1917 was a WWI-era French-designed 155 mm gun used by the French Army and the United States Army during the first half of the 20th century in towed and self-propelled mountings. His ...

field gun.

Development

The idea for the M12 was first proposed in 1941 and the pilot - T6 GMC - built and tested in early 1942. The

Army Ground Forces The Army Ground Forces were one of the three autonomous components of the Army of the United States during World War II, the others being the Army Air Forces and Army Service Forces. Throughout their existence, Army Ground Forces were the la ...

initially rejected the design as unnecessary, but after the Artillery Board supported the

Ordnance Department The United States Army Ordnance Corps, formerly the United States Army Ordnance Department, is a sustainment branch of the United States Army, headquartered at Fort Gregg-Adams, Virginia. The broad mission of the Ordnance Corps is to supply A ...

in asking for 50 units, 100 were authorized and built by March 1943. These vehicles were at first used for training.

Description

The M12 was built on the chassis of the M3 Grant tank. The engine was moved forward to the center of the vehicle to allow room for the gun mount, and most vehicles used later M4-style bogies with trailing return rollers. The armored compartment at the front was occupied by the driver and commander. The gun crew were located in an open-topped area at the back of the vehicle. It mounted a 155 mm gun M1917, M1918 or M1918M1, depending upon availability, a weapon derived from the nearly identical French 155 mm GPF gun of World War I vintage. The main armament had a traverse of 14° and elevation limits of +30° to -5°.Chamberlain, P. & C. Ellis (1969) ''British and American Tanks of World War II'', Arms and Armour Press, London, p. 145 Limited storage space meant that only 10 155 mm projectiles and propellant charges could be carried on the vehicle. An earth spade (similar to a bulldozer blade) at the rear was employed to absorb recoil. This layout (large gun mounted in an open mount at the rear, with a spade) was the pattern adopted for many years by other pieces of heavy self-propelled artillery.

Production

Only 100 vehicles were built: 60 in 1942 and a further 40 in 1943.

M30 cargo carrier

Given the limited ammunition carried in the M12, a support vehicle based on the same chassis was produced as the cargo carrier M30 to transport the rest of the gun crew, battery stores, and ammunition. Identical to the M12 except for the gun and recoil spade, it could carry 40 rounds of 155 mm ammunition, and was armed with a .50-caliber (12.7 mm)

M2 Browning machine gun The M2 machine gun or Browning .50-caliber machine gun (informally, "Ma Deuce") is a heavy machine gun that was designed near the end of World War I by John Browning. While similar to Browning's M1919 Browning machine gun, which was chamber ...

in a ring mount for self-defense. In operational conditions, the M12 and M30 would serve in pairs.Chamberlain & Ellis ''British and American Tanks of World War II'' p144

Use

During 1943, the vehicles were used for training or put into storage. From February to May 1944, before the invasion of France, 74 M12s were overhauled in preparation for combat operations overseas. They were assigned to six armored field artillery battalions (the 258th, 557th, 558th, 987th, 989th, and 991st) and employed successfully throughout the campaign in

North-West Europe Northwestern Europe, or Northwest Europe, is a loosely defined subregion of Europe, overlapping Northern and Western Europe. The term is used in geographic, history, and military contexts. Geographic definitions Geographically, Northwestern ...

. Although designed primarily for

indirect fire Indirect fire is aiming and firing a projectile without relying on a direct line of sight between the gun and its target, as in the case of direct fire. Aiming is performed by calculating azimuth and inclination, and may include correcting ...

, during assaults on heavy fortifications, the M12s were sometimes employed in a direct-fire role, such as in the Allied assault on the

Siegfried Line The Siegfried Line, known in German as the ''Westwall (= western bulwark)'', was a German defensive line built during the late 1930s. Started in 1936, opposite the French Maginot Line, it stretched more than from Kleve on the border with the ...

, where the M12 earned its nickname "Doorknocker" thanks to the 155mm cannon's ability to fire armour piercing rounds through seven feet of concrete at ranges up to 2,000 yards (1,830 meters). The vehicle was also dubbed "King Kong" by American operators due to the raw power of its gun. In 1945, the M12 was complemented in Europe by the M40 gun motor carriage, designed on a late-war M4A3 Sherman chassis with the

155 mm gun M1 The 155 mm gun M1 was a 155 millimeter caliber field gun developed and used by the United States military. Nicknamed "Long Tom" (an appellation with a long and storied history in U.S. field and naval artillery), it was produced in M1 and M ...

the successor to the 155mm M1918. Postwar, the M12 was retired from service and replaced by the M40.

Surviving vehicle

The sole surviving M12 GMC is displayed at the

Fort Sill Fort Sill is a United States Army post north of Lawton, Oklahoma, about 85 miles (137 km) southwest of Oklahoma City. It covers almost . The fort was first built during the Indian Wars. It is designated as a National Historic Landmark a ...

museum in

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

. It had previously been stored at the

United States Army Ordnance Museum The United States Army Ordnance Training Support Facility (formerly known as the U.S. Army Ordnance Training and Heritage Center and U.S. Army Ordnance Museum) artifacts are used to train and educate logistic soldiers. It re-located to Fort Gre ...

Aberdeen, Maryland Aberdeen is a city located in Harford County, Maryland, United States, northeast of Baltimore. The population was 16,254 at the 2020 United States census. Aberdeen is the largest municipality in Harford County. Aberdeen is part of the Baltimo ...

, United States, before being transferred to Fort Sill in November 2010.

References

Notes

Bibliography

* Leland Ness (2002) ''Janes World War II Tanks and Fighting Vehicles'', Harper Collins, *

External links

World War II vehicles
an

{{WWIIAmericanAFVs Self-propelled artillery of the United States World War II self-propelled artillery World War II armored fighting vehicles of the United States Cold War armored fighting vehicles of the United States 155 mm artillery Tracked self-propelled howitzers Military vehicles introduced from 1940 to 1944