37mm M3 gun

Even before war broke out in Europe, the Committee for the United States had launched the development of modern anti-tank weapons. They selected as their prototype the German 37mm PaK 35/36 anti-tank gun. However, the resulting instrument was significantly different from its German counterpart, although its influence can still be clearly observed. The M3 had a different bolt and carriage, as well as a longer barrel with different pitch rifling. The gun was equipped with a muzzle brake. 

Despite fairly impressive production, M3 was outdated fairly quickly. The increased armor of German tanks made this gun ineffective. In 1943-44, the M3 was replaced by the more powerful 56mm M1. However, in the Pacific theater the M3 was used successfully through the end of the war.