Harley-Davidson began producing the WLA in small numbers in 1940, as part of a general military expansion. The later entry of the United States into World War II saw significantly increased production, with over 90,000 being produced during the war (along with spare parts the equivalent of many more). Harley Davidson would also produce a close WLA variant for the Canadian Army called the WLC and would also supply smaller numbers to the UK, South Africa, and other allies, as well as filling orders for different models from the Navy and Marine Corps.

Unusually, all the WLAs produced after Pearl Harbour, regardless of the actual year, would be given serial numbers indicating 1942 production. Thus, war-time machines would come to be known as 42WLAs. This may have been in recognition of the use of the continued use of the same specification. Most WLCs were produced in 1943, and are marked 43WLC. The precise serial number, as well as casting marks, can be used to date a specific motor accurately, and some other parts bear year and month stamps. Frames and many other parts were not tagged with the serial number, and cannot generally be dated. (This is common prior to adoption of the VIN.)

Many WLAs would be shipped to allies under the Lend-Lease program. The largest recipient was the Soviet Union, which was sold over 30,000 WLAs.

Production of the WLA would cease after the war, but would be revived for the Korean War during the years 1949–1952.

Most WLAs in western hands after the war would be sold as surplus and "civilianized"; the many motorcycles available at very low cost would lead to the rise of the chopper and other modified motorcycle styles, as well as the surrounding biker culture. Many a young soldier would come home hoping to get a Harley-Davidson like he saw or rode in the service, leading to the post-war popularity of both the motorcycle and the company in general.

However, this also ensured that few nearly-original WLAs would survive in the US or even Western Europe. A significant number of WLAs were left in the Soviet Union, and either stored or put in private hands. With little access to parts and no chopper culture, and no export path to the West, many of those WLAs were preserved during the Cold War. Russia and other former Soviet countries are now a major source of WLAs and parts.

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