The M3 Gun Motor Carriage (GMC), known as T-12 pre-standardization, was a mobile tank-destroyer based on the White M3 Halftrack with a mounted M1897 or M2 75mm field gun. The gun and its shield were mounted in the cargo space of the halftrack, positioned to fire forward over the drivers compartment. The windshield area and windshield cover were modified to enable the gun to project to the front.
The M3 Gun Motor Carriage was standardized in November 1941 and was used in the defense of the Philippines as well as in the Operation Torch invasion of North Africa in 1942. The lightweight 75mm gun did well against thinly armored Japanese tanks, but German armor was much tougher and the 75mm cannon fire did not penetrate. The M3 GMC was used until mid-1944 after which it was considered obsolete.
For a time during World War II the M3 GMC was used as the insignia for Tank Destroyer Forces. AR 600-35, dated 13 March 1943, specified the design was a "75-mm gun, motor carriage M3, in gold color metal." The insignia was rescinded by Change 2, AR 600-35, dated 28 November 1944.
Almost invisible in the thick jungle vegetation, an M3 GMC supports Marine operations on Hill 660, Cape Gloucester, New Britain, December 1943 - January 1944. The barrel of the 75mm gun points to the left, just left of center.
M3 75mm Gun Motor Carriage halftracks, airbase security, North Africa during WW II.
M3 75mm Gun Motor Carriage, Special Weapons Company, 2nd Marine Division, Tinian, 30 July 1944.
M3 75mm Gun Motor Carriage, Italy, 1945. Second unit is to the right.