SM UC-55 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy () during World War I. The U-boat was ordered on 12 January 1916, laid down on 25 February 1916, and was launched on 2 August 1916. She was commissioned into the German Imperial Navy on 15 November 1916 as SM UC-55.
Design A Type UC II submarine, UC-55 had a displacement of when at the surface and while submerged. She had a length overall of , a beam of , and a draught of . The submarine was powered by two six-cylinder four-stroke diesel engines each producing (a total of ), two electric motors producing , and two propeller shafts. She had a dive time of 48 seconds and was capable of operating at a depth of .
The submarine had a maximum surface speed of and a submerged speed of . When submerged, she could operate for at ; when surfaced, she could travel at . UC-55 was fitted with six mine tubes, eighteen UC 200 mines, three torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one Uk L/30 deck gun. Her complement was twenty-six crew members.
Service In 6 patrols UC-55 was credited with sinking 9 ships, either by torpedo or by mines laid.
Loss UC-55 sailed from Heligoland on 25 September 1917 to lay mines in the Lerwick Channel, the southern approach to the port of Lerwick in the Shetland Islands. On 29 September, just as she started dropping her mines, she suffered a loss of trim which resulted in her diving beyond her rated maximum dive depth. This in turn resulted in the forward compartment flooding, the batteries failing, and chlorine gas developing. She was forced to surface to ventilate the boat, but when she surfaced, the rudder refused to answer the helm due to the lack of battery power. Her captain then gave orders to destroy secret documents and codebooks and set scuttling charges in the mine room and engine room. While the charges were being placed she was sighted by the armed trawler Moravia and the destroyers and .
A 12-pdr shell from the Sylvia hit the submarine's conning tower, killing her commander, Horst Ruhle von Lilienstern, and a second shell hit the hull and she began to sink, after which two depth charges were dropped right beside the UC-55, resulting in the U-boat blowing up. The Moravia then closed with the wreck, fired two more shots into her, and dropped a final depth charge. Of the submarine's crew, 17 were taken prisoner, and 10 were killed.
Location The wreck of UC-55 was discovered by side scan sonar lying on its keel on 3 July 1985, at a depth of at . The submarine's remains were noted to be approximately high and long.
On Friday 21 July 2023 the wreck was confirmed to be that of the UC-55 by the first divers to visit site.
Summary of raiding history DateNameNationalityTonnageTonnages are in gross register tonsFate9 March 1917440Damaged19 April 1917Bethlehem379Sunk21 April 1917Gerda979Sunk28 May 1917Asters1,531Sunk29 May 1917Clan Murray4,835Sunk30 May 1917Fernley3,820Damaged4 June 1917Clara923Sunk8 July 1917Spekulation291Sunk10 July 1917Flamma1,920Damaged12 July 1917Balzac1,720Sunk13 July 1917Lai509Sunk19 August 1917Rosario1,821Sunk
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