The Harley-Davidson XA (Experimental Army) was a flat-twin shaft drive motorcycle made by Harley Davidson for the US Army during World War II.
During WWII, the Army U.S. Army asked Harley-Davidson to design a specification of a motorcycle much like the BMWs used by German forces, with shaft drive, a Boxer Engine, and several other features that made the BMWs exceptionally reliable and low-maintenance machines. Harley was already producing the WLA, based on its traditional 45-degree V-twin but the army specifically wanted the one feature that the WLA didn’t have: shaft drive. So the company produced the XA, whose engine and drivetrain were based on the flathead BMW R71 (1938-1941) versus the overhead valve (OHV) BMW R75 (1941-1946). 1000 XAs were produced for evaluation. By the time production had begun, it was clear that the Jeep was the Army's general purpose vehicle of choice. The less advanced but cheaper WLA was considered sufficient for its limited roles. After the war, the BMW R71 would serve as the basis for the IMZ-Ural M72 (U.S.S.R./Russia) and the Chang Jiang CJ750 (China) which likewise pressed it into military service though parts should not be considered interchangeable across marques despite visual similarities.
According to the American Motorcyclist Association's Motorcycle Hall of Fame Museum, regarding the World-War-II-vintage Harley-Davidson XA, which has an opposed twin engine — "Mechanically, the large cooling fins stuck straight out in the breeze, reportedly keeping the XA’s oil temperature 100 °F (56 °C) cooler than a standard Harley 45." The latter was a transversely mounted V-twin, in which the air stream cannot reach the cylinders, especially the rear cylinder, as efficiently as on longitudinally mounted flat twin. In 1943, the XA's leading link fork was replaced with Harley-Davidson's first telescopic fork.
Though the XA motorcycle was "dead" as far as the military was concerned for full-blown production, both the side-valve and overhead-valve versions of the XA engine were explored according to Jerry Hatfield in his book "Inside Harley-Davidson" 1990 published by Motorbooks International. A 45 cu in (740 cc) overhead-valve version XA motor was sent to Detroit Wax Paper for testing as a generator set. OHV XA motors of 49 cu in (800 cc), with transmissions, were sent to Willys-Overland for testing as well as two blower-cooled XA motors for generators to be tested on tanks in 1943. There was even a Servi-Car prototype made called "The Model K" using the XA engine instead of the G motor planned for the 1946 model year.
After the 1st World War, The terms of surrender, imposed trough The Treaty of Versailles, prohibited Germany from producing any form of military machinery, including vehicles. This also meant, no large capacity motorcycles. The rising German administration of the 30's needed military equipment and thus developed a strategy to get around the restrictions by pursuing joint ventures with Russia . This was achieved by the signing of a 7 year trade agreement known as the Molotov- Ribbentrop pact, formally known as the Treaty of Nonaggression between Germany and the USSR . It was signed in Moscow on 10 ;23 August, 1939. At this time BMW's cooperation with Uralmoto Zavod was limited to the production of the BMW R71 classical motorcycle.
They kept the newly developed BMW R75 secrets for themselves. The non-aggression treaty lasted until Operation Barbarossa of 22 June, 1941 when Nazi Germany invaded the Soviet Union . In response, Russia joined forces with the Allies against Hitler. Russia retained certain BMW tooling and designs for the R71 motorcycle, and the Russian militarized R71 versions was designated the M72. This bike was almost identical to the BMW R71, and also featured the familiar horizontally opposed, 746 cc flat twin, side-valve engine.
In the spring of 1941 the BMW R75 was introduced. Built according to German war ministry instructions, without cost limitations. This high performance war machine had incredible off-road capabilities. The Wehrmachts new ride was soon recognized as one of the best motorcycles ever produced. They offered unprecedented mobility, performance and reliability on the battlefield at that time. Even Harley-Davidson copied the BMW design and delivered about 1,000 Harley-Davidson XA (Experimental Army) flat-twin shaft drive motorcycles to the US Army during World War II.
Having a great bike couldn't help the Germans win the war. After the German surrender, the Allies had full access to the shattered remains of Germany 's once impressive automotive industry.
The BMW motorcycle factory, which had been relocated to Eisenach during the war (and producing the BMW R75), fell into Russian hands as Eisenach was in Russian occupied territory.
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BMW R71 1938
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BMW R75 (enhanced military version)
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