Harley-Davidson XA

The Harley-Davidson XA, short for Experimental Army, was a flat-twin, shaft-drive motorcycle that Harley-Davidson built for the United States Army during the Second World War. The Army asked for a machine like the BMW R71 used by German forces, with shaft drive and a boxer engine for reliability and low maintenance, although Harley-Davidson was already building the V-twin WLA. The XA's engine and drivetrain were based on the side-valve BMW R71 rather than the overhead-valve R75. About 1,000 were produced for evaluation, but by then the Jeep had become the Army's general-purpose vehicle, no further XAs were ordered, and the cheaper WLA was judged sufficient. In 1943 its leading-link fork was replaced with Harley-Davidson's first telescopic fork. Its large cooling fins stood straight into the airflow and reportedly kept oil about 38 degrees Celsius cooler than a standard Harley 45.