SM UC-90

SM UC-90 was a German Type UC III minelaying submarine or U-boat in the German Imperial Navy (Kaiserliche Marine) during World War I. Completed in mid-1918, she saw no action during the war and was transferred to the Imperial Japanese Navy afterwards. The submarine briefly served in the IJN during 1920–1921 before she was partially dismantled and ultimately scrapped in 1926.

Design
A Type UC III submarine, UC-90 had a displacement of 491 t when at the surface and 571 t while submerged. She had a length overall of 56.51 m, a beam of 5.54 m, and a draught of 3.77 m. The submarine was powered by two six-cylinder four-stroke diesel engines each producing 300 PS (a total of 600 PS), two electric motors producing 770 PS, and two propeller shafts. She had a dive time of 15 seconds and was capable of operating at a depth of 75 m.

The submarine was designed for a maximum surface speed of 11.5 kn and a submerged speed of 6.6 kn. When submerged, she could operate for 40 nmi at 4.5 kn; when surfaced, she could travel 9850 nmi at 7 kn. UC-90 was fitted with six 100 cm mine tubes, fourteen UC 200 mines, three 50 cm torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one 10.5 cm SK L/45 or 8.8 cm Uk L/30 deck gun. Her complement was twenty-six crew members.

Construction and career
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. 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.