In 1939 Harley Davidson produced 2 39WLA models as prototypes for the US Army to test (along with models from Indian and Delco) at Fort Knox, Kentucky. After the war broke out in Europe the Army bought 400 WLAs designated 40WLA. By the time Japan attacked 41WLAs were common in the US Military. Between January 1942 and September 1945 HD delivered over 90,000 42WLAs to the US Military and Allies.
Though there were several configurations of 42WLA (each service had separate requirements in those days) the primary customer was the US Army. Though the Soviet Union steadfastly refused to acknowledge that they received any WLAs through Lend Lease Russia is now the primary source of parts for restorers. In 1942 HD built 1000 42XA models at the insistence of the US Army powered by a 45 CID horizontally opposed twin and shaft driven based on the BMW of the time.
The Harley Davidson 42WLA used a 45 CID (740 CC) air cooled side valve V-Twin motor with a three speed transmission that was good for a top speed of 65 MPH. Front suspension was girder and springs while the rear was rigid. There were a large number of options for the WLA based on unit requirements. Bags or Ammo Racks for the rear, scabbard for a Thompson Submachine Gun for the front forks. Almost all were issued with blackout lights fore and aft.
This particular 1942 Harley Davidson WLA is in Washington state and is listed as an original running survivor that was in a private collection for 40 years. Since no numbers are given it is impossible to know how correct this bike is. It almost certainly should have had a blackout headlight installed. There is no picture of the military service plate or the top of the tank and instruments. I would certainly ask the seller about that and those omissions leave me somewhat skeptical. The bike is currently priced at $7,995.00 with reserve not met
Sources:
Wikipedia
The Liberator (background, history)
Military Background (Background, History, Specs)
Bikez (specs)