SM UC-21

History
German Empire
Name:	UC-21
Ordered:	26 August 1915
Builder:	Blohm & Voss, Hamburg
Yard number:	271
Launched:	1 April 1916
Commissioned:	12 September 1916
Fate:	disappeared September 1917
General characteristics
Class and type:	German Type UC II submarine
Displacement:	417 t (410 long tons), surfaced 493 t (485 long tons), submerged
Length:	49.35 m (161 ft 11 in) o/a 39.30 m (128 ft 11 in) pressure hull
Beam:	5.22 m (17 ft 2 in) o/a 3.65 m (12 ft) pressure hull
Draught:	3.68 m (12 ft 1 in)
Propulsion:	2 × propeller shafts 2 × 6-cylinder, 4-stroke diesel engines, 500 bhp (370 kW) 2 × electric motors, 460 shp (340 kW)
Speed:	11.6 knots (21.5 km/h; 13.3 mph), surfaced 7.0 knots (13.0 km/h; 8.1 mph), submerged
Range:	9,430 nmi (17,460 km; 10,850 mi) at 7 knots (13 km/h; 8.1 mph), surfaced 55 nmi (102 km; 63 mi) at 4 knots (7.4 km/h; 4.6 mph), submerged
Test depth:	50 m (160 ft)
Complement:	26
Armament:	6 × 100 cm (39.4 in) mine tubes 18 × UC 200 mines 3 × 50 cm (19.7 in) torpedo tubes (2 bow/external; one stern) 7 × torpedoes 1 × 8.8 cm (3.46 in) Uk L/30 deck gun
Notes:	35-second diving time
Service record
Part of:	Flandern Flotilla 14 November 1916 – 30 September 1917
Commanders:	Oblt.z.S. Reinhold Saltzwedel 15 September 1916 – 9 June 1917 Oblt.z.S. Werner von Zerboni di Sposetti 10 June – 30 September 1917
Operations:	11 patrols
Victories:	98 merchant ships sunk (134,063 GRT) 5 merchant ships damaged (11,826 GRT) 1 ship captured as a prize (148 GRT) 1 warship damaged (778 tons)

SM UC-21 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 26 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 100 ships, either by torpedo or by mines laid. They included the British hospital ship Donegal, 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.

Like all pre-UC-25 German Type UC II submarines, UC-21 had a displacement of 417 tonnes (410 long tons) when at the surface and 493 tonnes (485 long tons) while submerged. She had a total length of 49.35 m (161 ft 11 in), a beam of 5.22 m (17 ft 2 in), and a draught of 3.65 m (12 ft). The submarine was powered by two six-cylinder four-stroke diesel engines each producing 250 metric horsepower (180 kW; 250 shp) (a total of 500 metric horsepower (370 kW; 490 shp)), two electric motors producing 460 metric horsepower (340 kW; 450 shp), and two propeller shafts. She had a dive time of 35 seconds and was capable of operating at a depth of 50 metres (160 ft).

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