After World War I, BMW was forced to cease aircraft (engine) production by the terms of the Versailles Armistice Treaty. The company consequently shifted to motorcycle production in 1923 once the restrictions of the treaty started to be lifted, followed by automobiles in 1928.
The circular blue and white BMW logo or roundel is often alleged to portray the movement of an airplane propeller, to signify the white blades cutting through the blue sky - an interpretation that BMW adopted for convenience in 1929, which was actually twelve years after the roundel was created. In fact, the emblem evolved from the circular Rapp Motorenwerke company logo, from which the BMW company grew. The Rapp logo was combined with the blue and white colors of the flag of Bavaria to produce the BMW roundel so familiar today.
BMW's first significant aircraft engine was the BMW IIIa inline-six liquid-cooled engine of 1918, much preferred for its high-altitude performance. With German rearmament in the 1930s, the company again began producing aircraft engines for the Luftwaffe. Among its successful WWII engine designs were the BMW 132 and BMW 801 air-cooled radial engines, and the pioneering BMW 003 axial-flow turbojet, which powered the tiny, 1944-45-era jet-powered "emergency fighter", the Heinkel He 162 Salamander, and was tested in the A-1b version of the world's first jet fighter, the Messerschmitt Me 262.