SM U-21 (Germany)

SM U-21 (rightmost boat in foreground)
History
German Empire
Name	U-21
Ordered	25 November 1910[1]
Builder	Kaiserliche Werft Danzig
Yard number	15[1]
Laid down	27 October 1911[1]
Launched	8 February 1913
Commissioned	22 October 1913
Fate	Sunk accidentally, 22 February 1919
Austria-Hungary
Name	U-36
Commissioned	21 September 1915
Decommissioned	1 October 1916
Fate	Returned to Imperial German Navy command
General characteristics
Class and type	German Type U 19 submarine
Displacement	650 t (640 long tons) surfaced 837 t (824 long tons) submerged
Length	64.15 m (210 ft 6 in)
Beam	6.10 m (20 ft)
Height	8.10 m (26 ft 7 in)
Draft	3.58 m (11 ft 9 in)
Propulsion	2 shafts 2 × MAN 8-cylinder two stroke diesel engines 2 × AEG double Motordynamos
Speed	15.4 knots (28.5 km/h; 17.7 mph) surfaced 9.5 knots (17.6 km/h; 10.9 mph) submerged
Complement	4 officers, 25 men
Armament	4 × 50 cm (19.7 in) torpedo tubes 1 × 8.8 cm (3.5 in) SK L/30 gun (from 1916 2 ×)
Service record
Part of:	Imperial German Navy: III Flotilla 1 August 1914 – 5 June 1915 Constantinople Flotilla 5 June 1915 – unknown end Pola Flotilla Unknown start – 4 March 1917 III Flotilla 4 March 1917 – 11 November 1918
Commanders:	Kptlt. Otto Hersing[2] 22 October 1913 – 31 August 1918 Kptlt. Friedrich Klein[3] 1 September – 11 November 1918
Operations:	11 patrols
Victories:	36 merchant ships sunk (79,005 GRT) 4 warships sunk (34,575 tons) 2 merchant ships damaged (8,918 GRT)

SM U-21 was a U-boat built for the Imperial German Navy shortly before World War I. The third of four Type U-19-class submarines, these were the first U-boats in German service to be equipped with diesel engines. U-21 was built between 1911 and October 1913 at the Kaiserliche Werft (Imperial Shipyard) in Danzig. She was armed with four torpedo tubes and a single deck gun; a second gun was added during her career.

In September 1914, U-21 became the first submarine to sink a ship with a self-propelled torpedo when she destroyed the cruiser HMS Pathfinder off the Firth of Forth. She also sank several transports in the English Channel and the Irish Sea later in the year, all in accordance with the cruiser rules then in effect. In early 1915, U-21 was transferred to the Mediterranean Sea to support the Ottoman Empire against the Anglo-French attacks during the Gallipoli Campaign. Shortly after her arrival, she sank the British battleships HMS Triumph and HMS Majestic while they were bombarding Ottoman positions at Gallipoli. Further successes followed in the Mediterranean in 1916, including the sinking of the French armoured cruiser Amiral Charner in February.

Throughout 1916, U-21 served in the Austro-Hungarian Navy as U-36, since Germany was not yet at war with Italy and thus could not legally attack Italian warships under the German flag. She returned to Germany in March 1917 to join the unrestricted commerce war against British maritime trade. In 1918, she was withdrawn from front line service and was employed as a training submarine for new crews. She survived the war and sank while under tow by a British warship in 1919.