SM UC-21
SM "UC-21" 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 29 August 1915 and was launched on 1 April 1916. She was commissioned into the German Imperial Navy on 12 September 1916 as SM "UC-21". In eleven patrols "UC-21" was credited with sinking 98 ships, either by torpedo or by mines laid. They included the British hospital ship , which "UC-21" torpedoed in the English Channel on 17 April 1917, killing 29 already wounded soldiers and 12 crew. "UC-21" disappeared after  departing Zeebrugge for the Bay of Biscay on 13 September 1917. Design. Like all pre-"UC-25" German Type UC II submarines, "UC-21" had a displacement of when at the surface and while submerged. She had a total length 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 35 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-21" 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.