The Northrop YB-49 was a prototype jet-powered heavy bomber aircraft developed by Northrop shortly after World War II. The prototype was first flown on 21st October 1947. Intended for service with the U.S. Air Force, the YB-49 featured a flying wing design. It was a jet-powered development of the earlier, piston-engined Northrop XB-35 and YB-35; the two YB-49s actually built were both converted YB-35 test aircraft. The YB-49 never entered production, being passed over in favor of the more conventional Convair B-36 Peacemaker piston-driven design. Design work performed in the development of the YB-35 and YB-49 nonetheless proved to be valuable to Northrop in the eventual development of the current day B-2 Spirit strategic bomber which first entered operational service in the 1990s.