The Gun Motor Carriage M3 was one of the many specialized variants built on the M3 halftrack APC. It was armed with an obsolete gun and didn't satisfy American requirements for a tank destroyer, but nevertheless this vehicle became the first mass produced American tank destroyer.
The German Blitzkrieg of May 1940 when German tank spearheads cleaved through French defenses like a hot knife through butter shocked the American military. The Americans suddenly realized that they did not have effective anti-tank weapons. Production of the 37 mm M3 gun was just beginning. Only 340 of these guns were built between July of 1940 and the start of 1941. On the other hand, the army had over 4000 75 mm M1897 guns (licensed copies of the French Mle. 1897) The ballistics of these weapons allowed them to combat all modern tanks, but the single trail and rigid carriage wheels made them awkward to transport. As a result, the Americans began to modernize these old guns, installing barrels from the M1897A4 on new M2A2 and M2A3 carriages with split trails and sprung wheels. There were also organizational changes put into effect. The Tank Destroyer Force was created as a fully fledged combat arm, on par with the Armor Force.
On a self propelled chassis
A meeting was held between representatives of the Ordnance Department and Army General Staff to determine the further development of anti-tank artillery. The main direction involved development of tank destroyer on a tank chassis, but this needed time. As an interim measure, the M1897A4 gun could be installed in the M3 halftrack APC. Its large troop compartment and lack of roof considerably simplified this conversion. The SPG had to be ready by the fall exercises.
Since the conversion was quite simple, the task of building the newly named 75 mm Gun Motor Carriage T12 fell to the workshops of the Aberdeen Proving Grounds. The troop compartment was emptied of benches, ammunition racks, and machine gun mounts. The two 30 gallon (114 L) fuel tanks in the front of the compartment were moved to the back. A welded steel box was installed behind the driver, which served as the pedestal for the gun mount and ready rack. The upper half of the M2A3 mount and M1897A4 gun with the existing gun shield were installed on top of the box. This whole assembly was designated 75 mm Gun Mount M3. The frame with the windscreen was removed, leaving only a folding armoured plate with vision slits.
|75 mm Gun Mount M3
|Prototype of the GMC T12.
|GMC T12 with a widened gun shield. This is a different design than the ones used on production GMC M3s.
Production and development
|GMC T12 from B company of the 93rd Tank Destroyer Battalion during exercises held in November of 1941.
|GMC T73 prototype.
|Placement of the crew in the GMC M3.
Name of shell
Penetration at 1000 yards at 30 degrees (homogeneous/surface hardened armour)
|Blueprints of the GMC M3
|A unit armed with GMC T12 tank destroyers.
|The GMC M3 played a large role in training tank destroyer crews. This photo was made in April of 1942 in Indio, California.
|GMC M3 in Tunisia.
|Elements of the 601st Tank Destroyer Battalion before the Battle of El Guettar. The vehicle closest to the camera is an M2A1 commander's halftrack.
|GMC M3 in Sicily. The vehicle is equipped with a 12.7 mm machine gun.
|A pair of British GMC M3 from the King's Dragoon Guards, Italy, May 1944.
|GMC M3s from the 27th Lancers in an indirect fire role. Italy, February 1945.
With the Marines
|A GMC M3 landing. The vehicle has two extra 12.7 mm machine guns in the fighting compartment and one extra 7.62 mm machine gun at the assistant driver's station.
|GMC M3 landing at Cape Gloucester, December 1943. A 7.62 mm M1919A4 machine gun can be seen on the right side.
|Marines with a GMC M3 on Bouganville.
|USMC M3s at Iwo Jima.