The North American Aviation B-45 was one of America's first operational bombers to employ jet propulsion. Designed during 1944 and 1945, the straight-wing Tornado was the first jet bomber in service with the U.S. Air Force and was the first four-jet aircraft to fly in the United States. Other versions include the longer-range B-45C with wing-tip tanks and the photoreconnaissance version, the RB-45C. Rated as a light bomber by modern-day standards, it was the first four-jet aircraft to drop an atom bomb and the first to be refueled in midair.