SM U-69

After the Austro-Hungarian Navy had competitively evaluated three foreign submarine designs, it selected the Germaniawerft 506d design, also known as the Type UD, for its new U-7 class of five submarines.[5] The Navy ordered five boats on 1 February 1913.[6]

The U-7 class was seen by the Austro-Hungarian Navy as an improved version of its U-3 class, which was also a Germaniawerft design.[6][Note 1] As designed for the Austro-Hungarian Navy, the boats were to displace 695 tonnes (684 long tons) on the surface and 885 tonnes (871 long tons) while submerged. The doubled-hulled boats were to be 69.50 metres (228 ft) long overall with a beam of 6.30 metres (20.7 ft) and a draft of 3.79 metres (12.4 ft). The Austrian specifications called for two shafts with twin diesel engines (2,300 metric horsepower (2,269 bhp; 1,692 kW) total) for surface running at up to 17 knots (31 km/h; 20 mph), and twin electric motors (1,240 PS (1,223 shp; 912 kW) total) for a maximum of 11 knots (20 km/h; 13 mph) when submerged.[6] The boats were designed with five 45 cm (17.7 in) torpedo tubes; four located in the bow, one in the stern. The boats' armament was to also include a single 6.6 cm (2.6 in) deck gun.[6]

U-10 was laid down on 7 February 1914,[2] and her construction was slated to be complete within 29 to 33 months.[6]

Neither U-10 nor any of her sister boats were complete when World War I began in August 1914.[7] With the boats under construction at Kiel, the Austrians became convinced that it would be impossible to take delivery of the boats, which would need to be towed into the Mediterranean past Gibraltar, a British territory.[6][Note 2] As a result, U-10 and her four sisters were sold to the Imperial German Navy on 28 November 1914.[1][Note 3]

U-10 was renumbered by the Germans as U-69 when her class was redesignated as the Type U 66. The Imperial German Navy had the submarines redesigned and reconstructed to German standards, which increased the surface displacement by 96 tonnes (94 long tons) and the submerged by 48 tonnes (47 long tons). The torpedo load was increased by a third, from 9 to 12, and the deck gun was upgraded from the 6.6 cm (2.6 in) gun originally specified to an 8.8 cm (3.5 in) Uk L/30 one.[1]

U-69 was launched on 24 June 1915.[1] On 4 September, SM U-69 was commissioned into the Imperial German Navy under the command of Kapitänleutnant Ernst Wilhelms.[2] On 4 March 1916, U-69 was assigned to the IV. U-Halbflotille.[8]

U-69 successfully completed five war patrols in which she sank 31 ships with a combined a total of 102,875 gross register tons (GRT). U-69's most successful month for number of ships sunk was April 1916, when she sank eight ships of 21,051 GRT in a span of six days. The month with the highest tonnage sunk was June 1917 when she sank five ships of 29,808 GRT in a nine-day span;[9] nearly half of that total came from one ship, the 13,441 GRT British armed merchant cruiser Avenger sunk on 14 June.[10] Avenger had been patrolling off the Shetland Islands and was returning to Scapa Flow, when she was struck by a single torpedo on the port side. The ship began listing heavily and non-essential crew were evacuated while destroyers arrived and took her under tow. Despite strenuous efforts to save her, Avenger foundered ten hours after being hit when her internal bulkheads collapsed. One man was killed in the attack.[11]

U-69 began her sixth and final patrol on 9 July when she departed from Emden, destined for operations off Ireland. U-69's position report at 02:30 on 11 July reported that she was 35 nautical miles (65 km; 40 mi) south of Lindesnes, Norway, and was the last known contact with U-69. According to author Dwight Messimer, two British sources report that HMS Patriot sank U-69 at position 60°25′N 1°32′E on 12 July. An observer in a kite balloon deployed by Patriot spotted a surfaced U-boat at 07:00. The U-boat submerged and Patriot hunted the submarine until noon, when it loosed two depth charges that brought thick brown oil to the surface. A postwar study by Germany cast doubt on whether or not the submarine attacked by Patriot was U-69. Officially, her fate remains unknown.[12]

• Helgason, Guðmundur. "WWI U-boats: U 69". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net.
• Photos of cruises of German submarine U-54 in 1916-1918.
• A 44 min. German film from 1917 about a cruise of the German submarine U-35.
• Room 40: Archived 2018-10-15 at the Wayback Machine original documents, photos and maps about World War I German submarine warfare and British Room 40 Intelligence from The National Archives, Kew, Richmond, UK.