75mm Gun Motor Carriage M3(T12) and M3A1
The urgent need for a tank destroyer to be rushed quickly into service led to the adaptation of the M3 half-track in June 1941 to take a suitably modified M1897A 75mm gun on a pedestal mount firing forward. The M1897A was the American version of the famous French “75”, dating from World War I, of which surplus stocks were available. Designated T12 GMC, the gun had a limited traverse and was provided with a shield. Despite its extemporary nature, this equipment proved most successful on trials and the vehicle was standardised as the M3 GMC in October 1941. First vehicles built were sent instantly to the Philippines at the end of 1941 in time to see action against the Japanese. Aside from wide use in the Pacific, M3 GMCs were also used by US forces in the North African (Tunis) campaign and on replacement by full-track tank destroyers, these vehicles were handed over to the British who used them (in Italy) until the end of the war. In British service the M3 GMC was known as the “75mm SP, Autocar” (Autocar being the builder of this model), and the vehicles were used in HQ troops of armoured car and tank squadrons to give support fire. Due to shortage of the original 75mm gun mount, later vehicles were produced with a modified mount under the designation 75mm Gun Motor Carriage M3A1. They were externally similar to the M3 GMC.
Adopted by the U.S. Marine Corps during the Second World War was the M3 Gun Motor Carriage (GMC), originally developed by the Ordnance Department as a tank destroyer for the U.S. Army. It was armed with a 75mm gun, the American-built copy of the French 75 from the First World War. Within U.S. Marine Corps divisions, it was found in the regimental antitank platoons and division antitank companies.
Due to the small number of Japanese tanks encountered by the Marines in the Pacific, the M3 GMC was primarily employed as an assault gun to deal with enemy defensive works. The vehicle would last in service with the marines until early 1945.
M6 Stop-Gap Tank Destroyer
In early 1941, the US Army decided it needed a wheeled tank destroyer armed with a 37mm anti-tank gun as quickly as possible. The Chrysler Corporation responded by mounting an armoured-shield protected 37mm anti-tank gun in the rear cargo bay of an unarmoured 0.75-ton 4 × 4 truck. It was labelled the M6 Gun Motor Carriage (GMC). Hereafter, all GMCs will be referred to as ‘tank destroyers’.
Series production of the M6 tank destroyer began in April 1942, with Chrysler building 5,380 units of the vehicle by October 1942. It was intended strictly as an interim design, until a better thought out wheeled tank destroyer could be developed and fielded. Despite being a stop-gap design, the M6 would be deployed to North Africa beginning in November 1942, during Operation Torch.
An observer of the M6 in North Africa stated the following in a March 1943 US Army report: ‘The sending of such a patently inadequate [tank] destroyer into combat can be best termed a tragic mistake.’ In an After-Action Report (AAR) titled Operations of the 1st Armored in Tunisia, Major General E.N. Harmon stated: ‘The 37mm self-propelled gun, mounted on the 0.75-ton truck, is positively worthless and has never been used in this division.’
United States Army interest in the half-track dated back to 1925 when the Ordnance Department purchased two Citroen-Kegresse semi-track vehicles from France. They bought another in 1931. US commercial firms undertook development work on half-tracks on behalf of the Ordnance Department and the first indigenous design, the T1 Halftrack, was built by Cunningham of Rochester, NY, in 1932. The development story of these vehicles in the thirties is beyond the scope of this book, but by 1939-40 Half-track Personnel Carrier T14 had been produced and became the prototype of all subsequent half-track types used by the US in World War II. In September 1940 the T14 was standardised as the Half-track M2 and, with modifications in order to transport personnel, it was standardised as the Half-track Personnel Carrier M3.
The M2 and M3 were similar in design and all major assemblies were interchangeable. The chassis and drive units were basically commercial components. The armoured hull was tin thick and included armoured shutters over the radiator, while armoured shields (tin thick) were provided for the cab windscreen and side windows. Vehicles were built with either an unditching roller mounted ahead of the front fender (though this was sometimes removed) or else with a winch. Late production vehicles also had stowage racks on the hull sides.
The M2 was basically a gun tower with the appropriate ammunition stowage facilities, and the M3 was a personnel carrier with slightly longer hull and rearranged seating. Contracts for production of these vehicles went to White and Autocar (M2) and Diamond T (M3) in September 1940.
In April 1943, work started on rationalising the half-track design to produce a “universal” vehicle with common body features suitable for either the gun tower/mortar carrier role or the personnel carrier role. This led to the M3A2 and M5A2 types from White/Autocar/Diamond T and International Harvester Co respectively. Standardisation of these revised designs took place in October 1943 but production was later cancelled. By this time, in fact, US Army interest in the half-track was beginning to wane and production of this type of vehicle tailed off completely in mid 1944, though half-tracks remained in wide service with the American forces until the war’s end. For artillery use the half-track was being displaced as a gun tower by the increasing availability of the high speed full-track tractor and in other service arms there was a growing preference for either full-track utility vehicles or trucks for personnel and supply work. In fact, half-tracks were never fully replaced in the period covered by this book though the process had started in 1944. Total US half-track production reached 41,169 units.
While the half-track was initially conceived as a fast reconnaissance vehicle, protected against small arms fire and with a good cross-country ability mainly for infantry and artillery use, it was also widely employed by other arms including the Armored Force as a “utility” vehicle. In this respect it was roughly equivalent in the US Army to the British Universal Carrier, but its larger size gave it more development potential as a weapons carriage. For the Armored Force, the Ordnance Department produced a number of expedient designs of gun motor carriage on the basis of the half-track and these performed useful “stopgap” service while superior full-track motor carriage designs were perfected. British armoured units also used a number of these half-track motor carriage types, supplied under Lend-Lease arrangements.