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 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, 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, seven torpedoes, and one Uk L/30 deck gun. Her complement was twenty-six crew members.