The Miles M.52 was a British supersonic research aircraft project which was undertaken in top secret between 1942 and 1945. The Air Ministry later cancelled the project for reasons that remain controversial to this day, while all of the existing work (including the highly critical, all-moving tailplane development) was sent to the Bell Aircraft company in the United States. Three months later, the U.S. government issued a requirement for a supersonic aircraft. Two years later, the Bell X-1 was the first plane to break the sound barrier in level flight.