SM U-35 was a German U 31-class U-boat which operated in the Mediterranean Sea during World War I. It ended up being the most successful U-boat participating in the war, sinking 220 merchant ships for a total of . Her longest serving captain was Lothar von Arnauld de la Perière. Under his command, U-35 sank 191 ships, making him the most successful submarine commander in history. Design German Type U 31 submarines were double-hulled ocean-going submarines similar to Type 23 and Type 27 subs in dimensions and differed only slightly in propulsion and speed. They were considered very good high seas boats with average manoeuvrability and good surface steering. U-35 had an overall length of , her pressure hull was long. The boat's beam was (o/a), while the pressure hull measured . Type 31s had a draught of with a total height of . The boats displaced a total of ; when surfaced and when submerged. U-35 was fitted with two Germania 6-cylinder two-stroke diesel engines with a total of for use on the surface and two Siemens-Schuckert double-acting electric motors with a total of for underwater use. These engines powered two shafts each with a propeller, which gave the boat a top surface speed of , and when submerged. Cruising range was at on the surface, and at under water. Diving depth was . The U-boat was armed with four torpedo tubes, two fitted in the bow and two in the stern, with carried 6 torpedoes. In 1915 U-35 was equipped with a Uk L/30 deck gun, which was replaced with a gun in 1916–17. The boat's complement was 4 officers and 31 enlisted men. Service history U-35s keel was laid on 20 December 1912 at the Friedrich Krupp Germaniawerft shipyard in Kiel. Its delivery date was supposed to be 1 March 1914, but it was delayed due to development problems with its diesel engines. U-35 officially entered service on 3 November 1914, under the command of Kapitänleutnant Waldemar Kophamel. The lead engineer was Hans Fechter. It sailed with the II Flottille, stationed in Heligoland. U-35 completed its first two deployments in reconnaissance actions in the North Sea. In its following three actions, U-35 sunk 17 merchant ships, for a total of . Later, it was paired with after a battle near Cattaro, Montenegro, and sunk two merchant ships for a total of . U-35 made two more voyages