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. The X-5 was based upon the design of a Messerschmitt P. 1101 airplane discovered in Germany at the end of World War II. It first flew on June 20 1951. Bell company test pilot Jean "Skip" Ziegler made the initial Phase I flights, to prove the airplane's airworthiness. The Bell X-5 was developed to check the feasibility of changing the sweep angle of an aircraft's wings in flight. This produce advantages from both an operational and research point of view. An operational aircraft could take off with its wings fully extended, reducing both its take off speed and the length of the runway needed.