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The Bell X-1 (Bell Model 44) is a rocket engine–powered aircraft, designated originally as the XS-1, and was a joint National Advisory Committee for Aeronautics–U.S. Army Air Forces–U.S. Air Force supersonic research project built by Bell Aircraft. Conceived during 1944 and designed and built in 1945, it achieved a speed of nearly in 1948. A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded in 1954.

In 1944, Miles was told to go ahead with the construction of three prototypes. In February 1946, with a first flight expected in the summer of 1946, the M52 was cancelled. In place of the manned full-scale M.52 it was decided to test 3/10 scale models of the aircraft, rocket propelled, dropped from an aircraft, and controlled by an autopilot. On the 10th of October 1948, a model achieved in level flight.