SM UC-90 was a German Type UC III 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 and was launched on 19 January 1918. She was commissioned into the German Imperial Navy on 15 July 1918 as SM UC-90."SM" stands for "Seiner Majestät" (His Majesty's) and combined with the U for Unterseeboot would be translated as His Majesty's Submarine. As with the rest of the completed UC III boats, UC-90 conducted no war patrols and sank no ships. She was surrendered to Japan on 1 December 1918. The U-boat was renamed O-4 for Japanese service from 1920 to 1921. In 1921 O-4 was partially dismantled at the Kure Navy Yard. Between 1924 and 1926, the hulk of O-4 was used as an antisubmarine warfare target before being sold for scrap.