SM U-70

SM U-70 was a Type U 66 submarine or U-boat for the German Imperial Navy (German: Kaiserliche Marine) during World War I. She had been laid down in February 1914 as U-11 the final boat of the U-7 class for the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or K.u.K. Kriegsmarine) but was sold to Germany, along with the others in her class, in November 1914.

The submarine was ordered as U-11 from Germaniawerft of Kiel as the last of five boats of the U-7 class for the Austro-Hungarian Navy. After the outbreak of World War I in August 1914, the Austro-Hungarian Navy became convinced that none of the submarines of the class could be delivered to the Adriatic via Gibraltar. As a consequence, the entire class, including U-11, was sold to the German Imperial Navy in November 1914. Under German control, the class became known as the U 66 type and the boats were renumbered; U-11 became U-70, and all were redesigned and reconstructed to German specifications. U-70 was launched in July 1915 and commissioned in September. As completed, she displaced 791 tonnes (779 long tons), surfaced, and 933 tonnes (918 long tons), submerged. The boat was 69.50 metres (228 ft) long and was armed with five torpedo tubes and a deck gun.

A part of the IV Flotilla throughout the war, U-70 sank 52 merchant ships with a combined gross register tonnage (GRT) of 135,288. Included in that total was Southland—at 11,899 GRT, one of the largest ships of the war sunk by a U-boat—sunk in June 1917. In addition she sank one British Flower-class sloop and damaged five merchant ships (24,971 GRT). On 20 November 1918, nine days after the Armistice, U-70 was surrendered to the British. She was broken up at Bo'ness in 1919–20.

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. The Navy ordered five boats on 1 February 1913.

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. 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 metric horsepower (1,223 shp; 912 kW) total) for a maximum of 11 knots (20 km/h; 13 mph) when submerged. 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.

U-11 was laid down on 11 February 1914, the final boat of the class begun. Her construction was slated to be complete within 29 to 33 months.

Neither U-11 nor any of her sister boats were complete when World War I began in August 1914. 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. As a result, U-11 and her four sisters were sold to the Imperial German Navy on 28 November 1914.

U-11 was renumbered by the Germans as U-70 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.