The M5 and M6 tank mounted variants were used in several models of armored vehicles most notably in the Stuart Light Tank M3/M5, the Lee Medium Tank M3, and Greyhound Light Armored Car M8. In addition, the M3 in its original version was mated to a number of other self-propelled carriages.
The inability of the 37mm round to penetrate the armor of mid-war tanks severely restricted the offensive capabilities of units armed with them.
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 some consideration had been given to replacing the machine guns with a more powerful anti-tank gun, the situation began to change only 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 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 that could be moved around by the crew, so any ideas of using a larger caliber than that of the German gun were discarded. The 37 mm was a popular caliber of anti-tank guns in the 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 was often referred to as a copy of it, the M3 differed significantly from the German design and used different ammunition.