The autogyro was resurrected after World War II when Dr. Igor Bensen, a Russian immigrant in the US, saw a captured German U-Boat's Fa 330 gyroglider and was fascinated by its characteristics. At work, he was tasked with the analysis of the British military "Rotachute" gyro glider designed by expatriate Austrian Raoul Hafner. This led him to adapt the design for his own purposes and eventually market the Bensen B-7 in 1955. Bensen submitted an improved version, the Bensen B-8M, for testing to the United States Air Force, which designated it the X-25. The B-8M was designed to use surplus McCulloch engines used on flying unmanned target drones.