 Additional M4s and M4A1s replaced M3s in U.S. tank battalions over the course of the North African campaign.The M4 and M4A1 were the main types in U.S. units until the fall of 1944, when the Army began replacing them with the preferred M4A3 with its more powerful engine.Some M4s and M4A1s continued in U.S. service for the rest of the war.