Its longest-serving captain was Walther Forstmann, who was awarded the Pour le Mérite during command on U-39. From January to mid-1917, Martin Niemöller served as U-39's coxswain. He is known as the author of the poem "First they came" which is inscribed at the New England Holocaust Museum. As an enemy of the Reich he was imprisoned from 1938-1945 in Sachenhausen and Dachau. In 1917 and 1918 Karl Dönitz served as watch officer on this boat. He later became Grand Admiral and Commander in Chief of the German Navy, and, for three weeks, the 4th President of Germany.