On 27 November 1944, the first prototype of the Boeing fighter took to the skies. This aircraft was the largest and heaviest single-piston-engined fighter ever developed in the United States. It was specifically designed to accommodate the powerful Pratt & Whitney Wasp Major engine, which drove an Aeroprop six-bladed contra-rotating propeller. The undercarriage of this aircraft was also noteworthy, as it employed a unique design patented by Boeing more than 10 years prior. Each of the main landing gear legs could be folded backward and rotated through 90 degrees, allowing the wheels to be stowed flat within the wings. This undercarriage design was later used by Curtiss fighters under a licensing agreement with Boeing.