Harley-Davidson’s 1942 military motorcycle with an opposed-cylinder engine was called the XA.
The XA was developed for the United States Army during World War II. Unlike Harley-Davidson’s familiar longitudinal V-twins, it used a horizontally opposed, shaft-driven engine inspired by the BMW R71 design. This layout was intended to improve cooling and reduce maintenance in desert conditions.
The motorcycle had a 45-cubic-inch flat-twin engine and a four-speed transmission. Harley-Davidson produced fewer than 1,000 examples before military priorities changed and the Army no longer required the model.
The XA is often confused with the WLA, Harley-Davidson’s much more numerous wartime motorcycle. The WLA used a conventional V-twin and chain drive, while the XA’s defining features were its opposed cylinders and shaft drive.