The Martin XB-48 was an American medium jet bomber developed in the mid-1940s. It competed with the Boeing B-47 Stratojet, which proved to be a superior design, and was largely considered as a backup plan in case the B-47 ran into development problems. It never saw production or active duty, and only two prototypes, serial numbers 45-59585 and 45-59586,"Fact Sheet: Martin XB-48." National Museum of the United States Air Force. Retrieved: 5 July 2010. were built.
