>> Harley-Davidson produced large numbers of motorcycles for the US Army in World War II

One of only two American cycle manufacturers to survive the Great Depression, Harley-Davidson again produced large numbers of motorcycles for the US Army in World War II and resumed civilian production afterwards, producing a range of large V-twin motorcycles that were successful both on racetracks and for private buyers.

Harley produced the WLC for the Canadian military.

Harley-Davidson, on the eve of World War II, was already supplying the Army with a military-specific version of its 45 cubic inches (740 cc) WL line, called the WLA. The A in this case stood for "Army". Upon the outbreak of war, the company, along with most other manufacturing enterprises, shifted to war work. More than 90,000 military motorcycles, mostly WLAs and WLCs (the Canadian version) were produced, many to be provided to allies. Harley-Davidson received two Army-Navy ‘E’ Awards, one in 1943 and the other in 1945, which were awarded for Excellence in Production.

Shipments to the Soviet Union under the Lend-Lease program numbered at least 30,000. The WLAs produced during all four years of war production generally have 1942 serial numbers. Production of the WLA stopped at the end of World War II, but was resumed from 1950 to 1952 for use in the Korean War.

The U.S. Army also asked Harley-Davidson to produce a new motorcycle with many of the features of BMW's side-valve and shaft-driven R71. Harley largely copied the BMW engine and drive train and produced the shaft-driven 750 cc 1942 Harley-Davidson XA. This shared no dimensions, no parts and no design concepts (except side valves) with any prior Harley-Davidson engine. 

Harley copied the BMW R71 to produce its XA model.

Due to the superior cooling of the flat-twin engine with the cylinders across the frame, Harley's XA cylinder heads ran 100 °F (56 °C) cooler than its V-twins. The XA never entered full production: the motorcycle by that time had been eclipsed by the Jeep as the Army's general purpose vehicle, and the WLA—already in production—was sufficient for its limited police, escort, and courier roles. Only 1,000 were made and the XA never went into full production. It remains the only shaft-driven Harley-Davidson ever made.
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