The Boeing B-29 Superfortress is a retired American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the USAAF and USAF during World War II and the Korean War. Named in allusion to its predecessor, the Boeing B-17 Flying Fortress, the Superfortress was designed for high-altitude strategic bombing, but also excelled in low-altitude night incendiary bombing and in dropping naval mines to blockade Japan. Silverplate B-29s dropped the atomic bombs on Hiroshima and Nagasaki, and remain the only system to deliver nuclear weapons in combat.