The North American B-25 Mitchell is an American medium bomber that was introduced in 1941 and named in honor of Brigadier General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theater of World War II, and after the war ended, many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 B-25s were built. It was the most-produced American medium bomber and the third most-produced American bomber overall. These included several limited models such as the F-10 reconnaissance aircraft, the AT-24 crew trainers, and the United States Marine Corps' PBJ-1 patrol bomber.