German submarine U-53 was a Type VIIB U-boat of Nazi Germany's Kriegsmarine during World War II. She was laid down on 13 March 1937 at Friedrich Krupp Germaniawerft in Kiel and went into service on 24 June 1939 under the command of Oberleutnant zur See (Oblt.z.S.) Dietrich Knorr. Design German Type VIIB submarines were preceded by the shorter Type VIIA submarines. U-53 had a displacement of when at the surface and while submerged. She had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two MAN M 6 V 40/46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two AEG GU 460/8-276 double-acting electric motors producing a total of for use while submerged. She had two shafts and two propellers. The boat was capable of operating at depths of up to . The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . U-53 was fitted with five torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one SK C/35 naval gun, 220 rounds, and one anti-aircraft gun The boat had a complement of between forty-four and sixty. Service history First patrol U-53 began her first patrol on 29 August 1939, just prior to the outbreak of the Second World War, under the command of Ernst-Günter Heinicke. Also aboard was Ernst Sobe, the commander of the 7th ("Wegener") Flotilla. U-53 sank two British ships on this patrol: the tanker SS Cheyenne and the freighter SS Kafiristan. Second patrol A second patrol under Heinicke, beginning on 21 October produced no results. U-53, along with and , was to penetrate the Strait of Gibraltar and raid Allied shipping in the Mediterranean Sea. Daunted by the strong British forces at the straits, Heinicke did not attempt to force them and was transferred to the merchant raider on his return to Germany. Third patrol Harald Grosse replaced Heinicke for U-53s third and final war patrol, which began on 2 February 1940. Grosse sank six ships for , including the Spanish neutral Banderas, whose sinking strained relations between Germany and Spain. On 23 or 24 February (sources vary), U-53 was engaged and sunk by depth