M3 Gun Motor Carriage

The M3 GMC was 20.46 feet (6.24 m) long, 7.29 feet (2.22 m) wide, 8.17 feet (2.49 m) high (including the gun shield), and weighed 20,000 pounds (9.1 t). Its suspension consisted of semi-elliptical longitudinal leaf springs for the wheels and vertical volute springs for the tracks, while its transmission consisted of constant mesh. Its ground clearance was 11.2 inches (280 mm). It had a White 160AX 147 horsepower (110 kW), 386 cubic inch (6,330 cc), 6-cylinder engine with a compression ratio of 6.44:1. It had a 150-mile (240 km) range, 60 US gal (230 L) fuel tank, a speed of 47 mph (75 km/h), and a power to weight ratio of 14.7 hp per ton. It was armed with one 75 mm M1897A4 with 59 rounds, had 0.25–0.625 in (6.4–15.9 mm) of armor, and a crew of five consisting of a commander, gunner, two loaders, and a driver. The M3 (with the M2A3 mount) could traverse 19° left and 21° right, elevate 29° and depress −10°. The M3A1 (using the M5 mount) could traverse 21° in both directions, but could only depress −6.5°. ==Development==

T12 / M3 After the fall of France, the U.S. Army studied the reasons behind the effectiveness of the German campaign against the French and British forces. One aspect that was highlighted by this study was the use of armored vehicles and self propelled artillery. However by 1941 there was little available in the U.S. Army's arsenal that could be used in such a role, the US Army decided that it required a 75 mm self-propelled gun. The Army had a number of M1897A5 guns, sufficient for the mass-production for such a weapon, and the M3 half-track was coming into production. After some debate, the Army decided to place M1897A5 guns on the M3 half-track chassis, which was designated the T12 GMC. The M1897A5 gun was originally adapted for the M3 chassis by placing it in a welded box riveted to the chassis behind the driver's compartment. It was accepted by the Army on 31 October 1941. The 36 T12s were improved in multiple ways. The improvements included the inclusion of a mount that raised the gun shield, the replacement of the original gun shield with a gun shield from the M2A3 (a carriage for the M1897A4), and the addition of a M2 Browning machine gun, which was later removed. After the final improvements were finished, the prototype vehicles were sent to the Autocar Company for production. The new vehicle entered production under the name M3 Gun Motor Carriage (or M3 GMC). M3A1 As the existing supply of M2A3 gun shields was insufficient to meet requirements for the production of the M3, the Ordnance Department developed the M5 gun shield, which replaced the M2A3. The new design was designated as the M3A1 Gun Motor Carriage (M3A1 GMC). ==Service history==

American use The T12/M3 GMC first saw action with the U.S. Army in the Philippines in 1941–42, six months after it was designed. Fifty were shipped on convoys to the Philippines in the late summer and fall of 1941. Three battalions of the Provisional Field Artillery Brigade operated T12s against the Japanese when they invaded the Philippines. During the early part of the campaign, the vehicle was used to provide direct covering fire and anti-tank support. The Japanese captured a few vehicles in 1942 and used them in the defense of the Philippines. Some M3s also saw service in Allied invasion of Sicily (Operation Husky), but by that time, the M10 tank destroyer had replaced it in the U.S. Army. A total of 1,360 M3 GMCs were also converted back into M3A1 half-tracks. The M3 also served with the U.S. Marines in the Pacific theater of Operations and was first used in the invasion of Saipan. It proved highly effective against the Japanese Type 95 Ha-Go light tank and the Type 97 Chi-Ha medium tank, in the fight against the Japanese 9th Tank Regiment on Saipan. It also served in the Battle of Peleliu and the Battle of Okinawa, and many other conflicts in the Pacific. Allied use The M3 GMC saw limited service with other countries as it was not widely supplied through the Lend-Lease program. A small batch of 170 vehicles was supplied to Britain, which used them in their Armoured Car Regiments which were the reconnaissance units of the armored formations. They were first used in the Tunisian Campaign with the Royal Dragoons. They were also used in Sicily, Italy, and later in France, but were gradually retired. The Free French Army also used M3s for training before receiving M10 tank destroyers. ==Production==

A total of 2,202 M3 GMCs were produced from 1941 to 1943. Only 86 vehicles were produced in 1941, but production increased to 1,350 in 1942, with the remaining 766 completed in 1943. Production was stopped due to the introduction of turreted, purpose-built, tank destroyers, such as the M10 GMC. ==See also==