The XR-7755-3 is the largest and most powerful reciprocating aircraft engine in the world. During World War II, the U.S. Army Air Force requested an engine with high takeoff power and low fuel consumption for a yet to be designed long-range bomber and transport. Lycoming began designing the engine in early 1944, and it was ready for testing by mid-1946. It featured nine dual-lobe overhead camshafts, which shifted axially for takeoff and cruising efficiency, and two-speed, geared, dual-rotation propeller drive. Lycoming built two XR-7755-3 prototypes. The company and the Army successfully tested them, but neither engine flew in an airframe. The proven reliability of the new gas turbine engines introduced after World War II made the XR-7755-3 obsolete before it could be fully developed. The engine displayed here is the sole survivor.