The 155 mm gun motor carriage M12 was a U.S. self-propelled gun developed during World War II. It mounted a 155 mm gun derived from the French Canon de 155 mm GPF field gun.
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°. 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.
Only 100 vehicles were built: 60 in 1942 and a further 40 in 1943.
