Navratil was born in Sarajevo in the Condominium of Bosnia and Herzegovina. He attended high school in Sarajevo, and finished cadet's school in Graz. In World War I he served in the Austro-Hungarian Armed Forces, as a fighter pilot in the Imperial and Royal Aviation Troops. While on the Eastern and Italian fronts, he scored a victory with Flik 41J on 14 April 1918, before assuming command of Flik 3J on 9 June 1918. Flying Albatros D.IIIs, he scored nine more victories.
