SM UC-55 was a German Type UC II

German Type UC II submarine

Type UC II minelaying submarines were used by the Kaiserliche Marine during the World War I. They displaced 417 tons, carried 7 torpedoes and up to 18 mines...

 minelaying

Minelayer

Minelaying is the act of deploying explosive mines. Historically this has been carried out by ships, submarines and aircraft. Additionally, since World War I the term minelayer refers specifically to a naval ship used for deploying naval mines...

 submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

 or U-boat

U-boat

U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

 in the German Imperial Navy  during World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. 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."SM" stands for "Seiner Majestät" (His Majesty's) and combined with the U for Unterseeboot would be translated as His Majesty's Submarine.

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

Heligoland

Heligoland is a small German archipelago in the North Sea.Formerly Danish and British possessions, the islands are located in the Heligoland Bight in the south-eastern corner of the North Sea...

 on 25 September 1917 to lay mines in the Lerwick Channel, the southern approach to the port of Lerwick

Lerwick

Lerwick is the capital and main port of the Shetland Islands, Scotland, located more than 100 miles off the north coast of mainland Scotland on the east coast of the Shetland Mainland...

 in the Shetland Islands

Shetland Islands

Shetland is a subarctic archipelago of Scotland that lies north and east of mainland Great Britain. The islands lie some to the northeast of Orkney and southeast of the Faroe Islands and form part of the division between the Atlantic Ocean to the west and the North Sea to the east. The total...

. 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 HMS Tirade and HMS Sylvia

HMS Sylvia (1897)

HMS Sylvia was a Violet-class destroyer of the Royal Navy . She was launched in Sunderland on the 3 July 1897, served in home waters and through World War I. She was broken up in 1920....

.

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.