Unrug was born in Brandenburg an der Havel into the Germanized family of Tadeusz Unrug, a major-general in the Prussian Army. After graduating from gymnasium in Dresden, Unrug completed Navy School in 1907 and began service in the German Navy. During World War I he commanded a U-Boot, earning promotion to the command of a submarine flotilla.
After Poland regained independence, Unrug left Germany and volunteered for the Polish Army. <...> Despite his problems with the Polish language, in 1925 he became commander of the Polish Navy.
In the latter camp he was the eldest-ranking officer and the commander of the Polish soldiers interned there. The Germans treated him with great respect as a former German officer by bringing former Imperial German Navy friends to visit him with the intention of making him switch sides. Unrug responded by refusing to speak German, saying that he had forgotten that language in September 1939. To the irritation of the Germans, Unrug would always insist having a translator present, even though he spoke his native German fluently. Unrug's spirit and unbowing attitude proved to be an inspiration to his fellow prisoners.