On 27 September 1913, Dönitz was commissioned as a Leutnant zur See (acting sub-lieutenant). When World War I began, he served on the light cruiser SMS Breslau in the Mediterranean Sea. In August 1914, the Breslau and the battlecruiser SMS Goeben were sold to the Ottoman navy; the ships were renamed the Midilli and the Yavuz Sultan Selim, respectively. They began operating out of Constantinople, under Rear Admiral Wilhelm Souchon, engaging Russian forces in the Black Sea. On 22 March 1916, Dönitz was promoted to Oberleutnant zur See. When the Midilli put into dock for repairs, he was temporarily assigned as airfield commander at the Dardanelles. From there, he requested a transfer to the submarine forces, which became effective in October 1916. He served as watch officer on U-39, and from February 1917 onward as commander of UC-25. On 5 September 1917, he became commander of UB-68, operating in the Mediterranean. On 4 October, after suffering technical difficulties, this boat was sunk by British forces and Dönitz was taken prisoner on the island of Malta.