37 Mm Gun M3 - Development History

Development History

In the mid-1930s, the United States Army had yet to field a dedicated anti-tank artillery piece; anti-tank companies of infantry regiments were armed with .50 in (12.7 mm) machine guns. Although there was some consideration had been given to replacing the machine guns with more a powerful anti-tank gun, the situation only began to change after the outbreak of the Spanish Civil War. Combat experience from Spain suggested that a light anti-tank gun, such as the German 37 mm PaK 35/36, was capable of neutralizing the growing threat posed by tanks.

In January 1937, the Ordnance Committee recommended development of a such a weapon; two PaK 36 guns were acquired for study. As the projected main user of the weapon, the Infantry branch was chosen to oversee the work. They wanted a lightweight gun which could be moved around by the crew, so any ideas of using a larger caliber than that of the German gun were discarded. It should also be noted that 37 mm was a popular caliber of anti-tank guns in 1930s; other anti-tank guns of the same caliber included Swedish Bofors gun, Czechoslovakian vz. 34 and vz. 37, Japanese Type 94 and Type 1.

Development and testing continued until late 1938. Several variants of gun and carriage were proposed until on 15 December a combination of the T10 gun and T5 carriage was officially adopted as the 37 mm Gun M3 and Carriage M4. Although the weapon followed the concept of the PaK 36 and often referred to as a copy of it, the M3 differed significantly from the German design and used different ammunition.

The gun was manufactured by Watervliet Arsenal and the carriage by Rock Island Arsenal. The first pieces were delivered early in 1940, the production continued until 1943.

Some minor changes in the gun construction were introduced during production. The carriage received a modified shoulder guard and traverse controls (carriage M4A1, standardized on 29 January 1942). Although Ordnance requested an upgrade of all M4 carriages to M4A1, this process was not completed. Another change was a threaded barrel end to accept a big five-port muzzle brake (gun M3A1, adopted on 5 March 1942). According to some sources, the latter was intended to avoid kicking too much dust in front of the gun, which hindered aiming; however, the brake turned out to be a safety problem when firing canister ammunition and consequently the M3A1 went into combat without the muzzle brake. Other sources mention the muzzle brake was intended to soften a recoil and they say that it was dropped simply because additional recoil control measures were not really needed.

In an attempt to increase the armor penetration of the M3, several squeeze bore adapters (including the British Littlejohn adaptor) were tested; none were adopted. Experiments with rocket launchers on the M4 carriage (e.g. 4.5 in (110 mm) rocket projector T3) did not produce anything practical either.