The X-5 was the world's first airplane to vary the sweepback of its wings in flight. It was built to prove the theory that by increasing the sweepback of an airplane's wings after takeoff, a higher maximum speed could be obtained, while still retaining low takeoff and landing speed and higher rate of climb with the wings swept forward. The X-5 was based upon the design of a Messerschmitt P. 1101 airplane discovered in Germany at the end of World War II, although the P. 1101 could vary its sweep only on the ground.
The first X-5 flight was made on June 20, 1951. On the airplane's ninth flight, its wings were operated through the full sweep range of 20 to 60 degrees.
Two X-5s were built and flown. One crashed and was destroyed on October 13, 1953 when it failed to recover from a spin at 60 degrees sweepback. The other was delivered to the U.S. Air Force Museum in March 1958.