Named after General "Billy" Mitchell, America's foremost supporter of air power, the B-25 Mitchell first flew on Aug. 19, 1940, and was the first multi-engine design to go beyond the prototype stage. North American Aviation built more than 11,000 B-25s for the U.S. Army Air Forces and the U.S. Navy, which called it the PBJ, plus 50 each for China and Great Britain. The B-25 bomber had a wingspan of 67 feet and was 52 feet 11 inches long. One version, the B-25H, was the most heavily armed attack bomber of its time, with a 75-millimeter gun, up to 14 .50 caliber machine guns and 5,000 pounds of bombs carried in an internal bomb bay.