Not technically true. They were commissioned during WW2 to design and make an engine that could hang with the Germans and basically copied the design from BMW. They called it the XA. It was a flat twin and shaft driven, and ran about a hundred degrees cooler than the V due to the fins being out in the air. But God forbid Harley stick with an efficient and long lasting design, so they discontinued them after the Army leaned more into the Jeep, and only a thousand of them were made.
Jason