The M3 was the first US antitank gun adopted, and it didn't enter service until 1940. By 1942 it was obsolete in Europe, although it continued to be effective in the Pacific theater, and when used against light armored vehicles, pillboxes, and other emplacements. It was a simple and reliable weapon, and served as armament on several tanks and vehicles (Stuart, Lee/Grant, Greyhound, and others) itself as well as being an antitank gun.