Type U 51 was a class of U-boats built during World War I by the Kaiserliche Marine. Six Type U 51 were ordered at the beginning of the war and these were commissioned in 1916. Two were lost during the war and the remaining four surrendered to the Allies and were scrapped.
Design When World War I broke out on 28 July 1914, the German Navy initiated an emergency war building program, the so-called mobilisation program. This Mobilisation called for the immediate construction of seventeen U-boats by the two submarine building shipyard in Germany: the Germaniawerft in Kiel and the Kaiserliche Werft Danzig. The Kaiserliche Werft received an order for five Type U 43 U-boats and the Germaniawerft would have received an order for the remaining twelve U-boats, but since this yard experienced serious delays in the delivery of the previous order of eleven Type U 31 U-boats, only six Type U 51 U-boats were ordered on 23 August 1914 and the remaining six were ordered from a new yard AG Weser.
The previous two types of diesel engine U-boats produced by the Germaniawerft, the Type U 23 and Type U 31 had two-stroke diesel engines produced by the same shipyard, but since these engines were not sufficient reliable, four-stroke MAN diesel engines were to be installed. Delivery of these U-boats was expected between December 1915 and December 1916.
Characteristics Type U 51s had an overall length of The boats' beam was , the draught was , with a total height of . The pressure hull had a length of and had a diameter of . The boats displaced when surfaced and when submerged.
Type U 51s were fitted with two MAN six-cylinder four-stroke S6V45/42 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, which gave the boats a top surface speed of , and when submerged. Cruising range was at on the surface and at submerged. Constructional diving depth was .
The U-boats were armed with four torpedo tubes, two fitted in the bow and two in the stern, and carried seven torpedoes. Most boats received initially one or two SK L/30 deck guns. Some boats had their sole deck gun replaced with a SK L/45 gun. The boats' complement was four officers and thirty-two enlisted men.
Ships +NameLaunchedCommissionedMerchant ships sunk(nbr / GRT )Fate 25 November 191524 February 1916noneLost on 14 July 1916 in the Ems estuary 8 December 191516 March 191628 / 71.225Surrendered on 21 November 1918 and scrapped at Swansea in 1922 1 February 191622 April 191683 / 217.508Surrendered on 31 December 1918 and scrapped at Swansea in 1922 22 February 191625 May 191626 / 68.228Surrendered on 24 November 1918 and scrapped at Taranto in 191918 March 19168 June 191661 / 129.352Surrendered on 26 November 1918 and scrapped at Sasebo in 192218 April 191623 June 19164 / 5.374Missing in the Arctic Ocean after 2 November 1916
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