Shortly before World War II in April 1940, 3rd Battalion was again reactivated. The fighting in World War II found the Marines of 3/5 at Guadalcanal, New Britain, Peleliu, and Okinawa. At Peleliu, they were the last Marine battalion to be shipped out before the army took over. In April 1946, their mission accomplished, 3rd Battalion was disbanded and most of the Pacific veterans returned to civilian life.