The Two Knucklehead Trikes of WWII
During WWII, Harley-Davidson made numerous prototypes hoping to land one of the many lucrative military contracts available to help the war effort. They hit a home run with the WLA model and the dream of another huge contract kept HD engineers busy throughout the war. One complaint that they US military had with motorcycles was that it took special training to operate one. Harley had already solved this problem for police departments with the Servi-car, so they thought a more powerful offroad capable version might just be what the military needed.
The first prototype started with a 68 cubic inch Knucklehead motor mated to a standard three speed with reverse transmission. The rear wheels were powered via a chain, just like a conventional motorcycle. This setup proved unsatisfactory, perhaps due to the maintenance issues with the chain, so Harley built a second prototype with used a new shaft drive instead of the chain.
The shaft driven model was called the “TA” and after the prototype was successfully tested for the US Army, they put in an order for 16 units. This paled in comparison to tens of thousands of WLAs that Harley had been producing, but it turned out that the TA had stiff competition from a new easy to drive, offroad capable vehicle known as the Jeep. Once the US Military realized how versatile the Jeep was, they soon began to move away from using motorcycles altogether.