 Germany's "Luftstreitkräfte" (the army air service of the German Imperial Army) first officially adopted the "Balkenkreuz" in mid-April 1918 (about a week before the death of Manfred von Richthofen), and used it from that time until World War I ended in November 1918.The IdFlieg directive of 20 March 1918 to all manufacturers states in the first sentence (translated to English)