World War 2 In Review: M12 GMC

The 155 mm Gun Motor Carriage M12 was a U.S. self-propelled gun developed during the Second World War. It mounted a 155 mm gun derived from the French Canon de 155mm GPF field gun.

The idea for the M12 was first proposed in 1941 and the pilot - T6 GMC - built and tested in early 1942. The Army Ground Force initially rejected the design as unnecessary but after the Artillery Board supported the Ordnance Department 100 were authorized and built. These were used for training.

The M12 was built on the chassis of the M3 Lee tank. It had an armored driver's compartment shared with the commander, but the gun crew were located in an open topped area at the back of the vehicle. The engine was moved forward to the center of the vehicle and most vehicles used M4 bogies with trailing return rollers. It mounted a 155 mm gun M1917, M1917A1 or M1918 M1, depending upon availability, a weapon derived from the nearly identical French 155 mm GPF gun of World War I vintage. Limited storage space meant that only 10 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 heavy self-propelled artillery.

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

Production of M12

September 1942: 1

October 1942: 37

November 1942: 12

December 1942: 10

January 1943: 16

February 1943: 19

March 1943: 5

Total: 100

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 gun crew and additional ammunition.

Identical except for the gun and recoil spade, it could carry 40 rounds of 155 mm ammunition, and was armed with a .50-caliber Browning M2 machine gun in a ring mount.

In operational conditions, the M12 and M30 would serve in pairs.

During 1943, the vehicles were used for training or put into storage. Before the invasion of France, 74 M12s were overhauled in preparation for combat operations. They were employed successfully throughout the campaign in North-West Europe. Although designed primarily for indirect fire, 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, where the M12 earned its nickname "Doorknocker" thanks to the 155mm cannon's ability to pierce seven feet of concrete at ranges up to 2,000 yards (1,830 meters) (ironically the same epithet was given to the 37mm guns on the early Panzer III tank due to its inability to penetrate modern armored vehicles). 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. Postwar, the M12 was retired from service and replaced by the M40.

Type: Self-propelled gun

Place of origin: United States

In service: 1942–1945

Used by: United States

Wars: World War II

Designed: 1942

Manufacturer: Pressed Steel Car Company

Produced: September 1942 – March 1943

Number built: 100

Weight: 59,000 lb (26.8 metric tons)

Length:

22 ft 1 in (6.73 m) hull, spade retracted

22 ft 2.5 in (6.77 m) including gun

Width: 8 ft 9 in (2.66 m) without sand shields

Height: 9 ft 5.5 in (2.88 m) over gun shield

Crew: 6 (Commander, driver, 4 gun crew) with remaining gun crew in M30

Armor: 0.5 to 2 in (12.7 to 50.8 mm)

Main armament: 155 mm (6.1 inch) M1917, M1918, or M1918M1 gun in Mount M4; 10 rounds

Engine: Wright R975 C1; 350 hp (261 kW) at 2,400 rpm

Power/weight: 13.06 hp/metric ton

Suspension: Vertical volute spring suspension (VVSS)

Operational range: 140 mi (230 km)

Speed: Road: 21–24 mph (34–39 km/h)

Surviving Vehicle

The sole surviving M12 GMC is displayed at the Fort Sill museum in Oklahoma. It had previously been stored at the United States Army Ordnance Museum in Aberdeen, Maryland, United States, before being transferred to Fort Sill in November 2010.

Left side view of the 155mm Gun Motor Carriage M12 (s/n 4055516), General Motors Proving Ground, 8 November 1942.

Right side view of the 155mm Gun Motor Carriage M12 (s/n 4055516), General Motors Proving Ground, 8 November 1942.

The M12 155mm Gun Motor Carriage was built on both the M4 (illustrated) and M3 medium chassis. Note that the vehicles have been driven up onto wooden stands to increase the range of the guns in indirect fire mode.

M12 Gun Motor Carriage. 155mm gun on M3 medium tank chassis.

T6 155mm Gun Motor Carriage prototype.

M12 Gun Motor Carriage.

M12 Gun Motor Carriage, "Aiming Circle Annie," 558th Field Artillery Battalion, with the recoil spade dug in, firing across the Moselle River, France, 1944. Dick Smuin firing the gun, Sgt. Marcelo and Bill DePauw standing, and Baten kneeling.

T6 155mm Gun Motor Carriage prototype.

155mm Gun Motor Carriage M12 (s/n 4055526).

M12 Gun Motor Carriages, 174th Field Artillery Battalion.

M12 Gun Motor Carriage, "Dead Line," 557th Field Artillery Battalion.

M12 Gun Motor Carriage, "Betty," 557th Field Artillery Battalion.

M12 Gun Motor Carriage, "Hari-Kari," 557th Field Artillery Battalion.

The 155mm Gun Motor Carriage M12, attached to the 103rd Infantry Division, U.S. Seventh Army, was called upon to blast pillbox defenses in the Siegfried Line. The M12 could carry 10 rounds on board. Besides those 10 rounds, it was designed to work in tandem with an accompanying M30 cargo carrier, which could carry an additional 40 rounds plus the gunnery crew for the M12. Note the barrel of a camouflaged 57mm anti-tank gun in the foreground. Niederschlettenbach, Germany, 20 March 1945.

M12 Gun Motor Carriage, 991st Field Artillery Battalion, firing near Aachen, Germany, October 1944. Photo taken from the rear of an M30 Cargo Carrier. A German PzKpfw. V "Panther" tank is just visible in the distance at far right.

Hmmm… this looks familiar… While the two crew members and vehicles are exactly the same in this photo as the one above, the backgrounds are totally different. Clearly one has had a different background added to it. My guess is this photo is the faked photo and was created to satisfy the censors, as the building in the above photo could be used to determine exactly where the photo was taken. The above photo is also much clearer, an indication that this photo has been altered.

M12 Gun Motor Carriage, 987th Field Artillery Battalion, near Bayeaux, France, 10 June 1944.

Right rear view of M12 Gun Motor Carriage.

M12 Gun Motor Carriage ready for firing, 1943.

M12 Gun Motor Carriage firing at German positions, March 1945.

M12 Gun Motor Carriage firing on enemy installations in support of the 11th Armored Division near Pruem, Germany, February 1945. The gun in the foreground is "Alberta IV."

M12 Gun Motor Carriage, "June Gil," 987th Field Artillery Battalion, St. Lo, France, 16 July 1944. Also chalked on the side is the inscription, "Avant le char de mort," "Forward tank of death."

M12 Gun Motor Carriage, "Corregidor," firing on German positions near St. Lo, France, 1944.

Gun crew of the M12 Gun Motor Carriage, "The Babe," loading a round into the gun during the bombardment of Fort Driant, part of the Metz fortifications, 10 October 1944.

Gun crew commander of a M12 Gun Motor Carriage on the lookout for targets while supporting the 3rd Armored Division near Houffalize, December 1944.

M12 Gun Motor Carriage in action.

Rear view of the M12 Gun Motor Carriage.

Top view of the M12 Gun Motor Carriage.

Right side view of the M12 Gun Motor Carriage.

Left rear view of the M12 Gun Motor Carriage with spade elevated for travel.

M12 Gun Motor Carriage, Belgium, January 1945.

M12 Gun Motor Carriage, "The Persuader," Battery B, 557th Field Artillery Battalion, moving across a treadway bridge near Linnich, Germany, 26 February 1945.

M12 Gun Motor Carriage slogging through the mud while supporting the 5th Infantry Division in its attacks on the Siegfried Line, Luxembourg, 9 February 1945.

M12 Gun Motor Carriage (4081011, serial no. 59), Battery C, 557th Field Artillery Battalion, near Morteau, France, 15 November 1944. Note the folding chocks placed under the front tracks, and also the hoops for the camouflage net erected over the gun compartment. This vehicle is unusual in that it is still fitted with the front portion of the sand skirts, a feature not commonly seen on M12 GMCs in Europe.

M12 Gun Motor Carriage, "Choo-Choo-Bam" (4081040, serial no. 88) providing fire support for Patton's Third Army during fighting in Echternach, Luxembourg, 8 February 1945. Note the extended end connectors on the tracks.

M12 Gun Motor Carriage, "Adolph's Assassin," Battery A, 991st Field Artillery Battalion, preparing to fire, near Kornelmunster, Germany, 4 November 1944.

Gun crew loading a projectile into the breech of an M12 Gun Motor Carriage. The shell and bagged propellant charge were loaded separately .

M12 Gun Motor Carriages, 987th Field Artillery Battalion, coming ashore on King sector, Gold Beach, Normandy, 7 June 1944. They were attached to the British 50th Infantry (Northumbrian) Division, reattached to the American Army on 1 July.

Gun crew loading shell into breech of M12 Gun Motor Carriage, 558th Field Artillery Battalion.

M12 Gun Motor Carriages of the 55th Field Artillery Battalion during training.

A battery of M12 Gun Motor Carriages of the 558th Field Artillery Battalion leaving the range after a day's shooting.

First in a series showing an M12 Gun Motor Carriage firing. Here the gun crew stand at their ready positions. 558th Field Artillery Battalion.

Another in the series showing an M12 Gun Motor Carriage firing. The gunner has just pulled the firing lanyard.

Another in a series showing an M12 Gun Motor Carriage being fired. The recoil raises a cloud of dust; the firing lanyard is in the gunner's hand.

Another in the series showing an M12 Gun Motor Carriage being fired. The gun is starting to recover from the recoil position.

M12 Gun Motor Carriages of the 558th Field Artillery Battalion in staggered line during training.

M12 Gun Motor Carriage and M30 Cargo Carrier, 558th Field Artillery Battalion.

M12 Gun Motor Carriage, "Buccaneer," 557th Armored Field Artillery Battalion, preparing to fire on German positions during the assault on the Roer River, 25 November 1944.

Given the limited ammunition carried in the M12 GMC, a support vehicle based on the same chassis was produced as the Cargo Carrier M30. It was designed to transport the gun crew and additional ammunition. The M30, which could carry 40 rounds of 155mm ammunition, was armed with a .50 cal. Browning M2 machine gun in a ring mount. In operational conditions, the M12 and M30 would serve in pairs.