37 mm Gun M3
The 37 mm Gun M3 was the first dedicated anti-tank gun fielded by United States forces in numbers. Introduced in 1940, it became the standard anti-tank gun of the U.S. infantry with its size enabling it to be pulled by a jeep. However, the continuing improvement of German tanks quickly rendered the 37 mm ineffective, and by 1943 it was being gradually replaced in the European and Mediterranean theaters by the more powerful British-developed 57 mm Gun M1. In the Pacific, where the Japanese tank threat was less significant, the M3 remained in service until the end of the war.
Additional Information: en.wikipedia.org/wiki/37_mm_Gun_M3