Returning to Germany, Arnauld volunteered for the Imperial Naval Air Service (Zeppelins), but he was recalled by von Pohl. He then volunteered for U-boat service, and on completing submarine school, in October 1915 he took command of the U-35 based at Pola on the Adriatic. From November 1915 to March 1918, Arnaud completed 14 cruises with the Pola Flotilla. During one cruise alone in 1916, he sank 54 ships totaling more than 90,150 tons. In March 1918, Arnaud took command of the U-139 in the Atlantic. During his wartime total of 16 patrols, Arnauld sank 196 ships totaling 455,716 tons. This record stands unsurpassed in both world wars and indeed all history.
Retained in the German navy following World War I, Arnauld filled staff billets and commanded the light cruiser Emden from 1928 to 1930. He left the navy in 1931 as a captain and subsequently taught at the Turkish Naval Academy from 1932 to 1938. Recalled to the German navy at the start of World War II, Arnauld subsequently served as naval commander in Belgium, the Netherlands, Brittany, and western France. Promoted to vice admiral and named Admiral Southeast, he died in a plane crash at Le Bourget airport in Paris on 24 February 1942 en route to take up his new command. Dana Lombardy and T. P. Schweider
Grey, Edwin A. The U-Boat War, 1914–1918. London: Leo Cooper, 1972.; Miller, David. U-Boats. Washington, DC: Brassey's, 2001.; Tarrant, V. E. The U-Boat Offensive, 1914–1945. Annapolis, MD: Naval Institute Press, 1989.
Dana Lombardy and T. P. Schweider