SM U-20^{[Note 1]} was a German Type U 19 U-boat built for service in the Imperial German Navy. She was launched on 18 December 1912, and commissioned on 5 August 1913. During World War I, she took part in operations around the British Isles. U-20 became infamous following her sinking of the British ocean liner RMS Lusitania on 7 May 1915, an act that dramatically reshaped the course of World War I.

Quick Facts History, German Empire ...

U-20 (second from left) in Kiel harbour, 1914
History
German Empire
Name	U-20
Ordered	25 November 1910
Builder	Kaiserliche Werft Danzig
Cost	2,450,000 Goldmark
Yard number	14
Laid down	7 November 1911
Launched	18 December 1912
Commissioned	5 August 1913
Fate	Grounded 4 November 1916 and destroyed by her crew the next day.
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	7.30 m (23 ft 11 in)
Draught	3.58 m (11 ft 9 in)
Propulsion	2 shafts 2 × MAN 8-cylinder two stroke diesel motors with 1,700 PS (1,250 kW; 1,680 shp) 2 × AEG double Motordynamos with 1,200 PS (880 kW; 1,180 shp) 320 rpm submerged
Speed	15.4 knots (28.5 km/h; 17.7 mph) surfaced 9.5 knots (17.6 km/h; 10.9 mph) submerged
Range	9,700 nautical miles (18,000 km; 11,200 mi) at 8 kn surfaced 80 nautical miles (150 km; 92 mi) at 5 kn submerged
Test depth	50 m (164 ft 1 in)
Boats & landing craft carried	1 dinghy
Complement	4 officers, 31 men
Armament	4 × 50 cm (19.7 in) torpedo tubes (2 each bow and stern) with 6 torpedoes 1 × 105 mm gun
Service record
Part of:	III Flotilla 1 August 1914 – 4 November 1916
Commanders:	Kptlt. Otto Dröscher[1] 5 August 1913 – 15 December 1914 Kptlt. Walther Schwieger[2] 16 December 1914 – 5 November 1916[3]
Operations:	7 patrols
Victories:	37 merchant ships sunk (145,830 GRT) 1 merchant ship damaged (2,246 GRT) 1 warship damaged (397 tons)

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On 7 May 1915, U-20 was patrolling off the southern coast of Ireland under the command of Kapitänleutnant Walther Schwieger. Three months earlier, on 4 February, the Germans had established a U-boat blockade around the British Isles and had declared any vessel in it a legitimate target.

At about 13:40 Schwieger was at the periscope and saw a vessel approaching. From a distance of about 700 metres (770 yd) Schwieger noted she had four funnels and two masts, making her a liner of some sort. He recognised her as the Lusitania, a vessel in the British Fleet Reserve, and fired a single torpedo. It hit on the starboard side, almost directly below the bridge. Following the torpedo's explosion, the liner was shattered by a second explosion, possibly caused by coal dust, a boiler explosion, or an explosion in the propulsion system – so large Schwieger himself was surprised. In 18 minutes, Lusitania sank with 1,199 casualties. The wreck lies in 300 feet (91 m) of water.

Fifteen minutes after he had fired his torpedo, Schwieger noted in his war diary:

"It looks as if the ship will stay afloat only for a very short time. [I gave order to] dive to 25 metres (82 ft) and leave the area seawards. I couldn't have fired another torpedo into this mass of humans desperately trying to save themselves."

There was at the time a great controversy about the sinking, over whether Lusitania was smuggling contraband war material to England and over the number of torpedoes Schwieger fired. The Allies and the United States originally thought the U-20 fired two torpedoes. Postwar investigations showed only one was fired.

Before he got back to the docks at Wilhelmshaven for refuelling and resupply, the United States had formally protested to Berlin against the brutality of his action.

Kaiser Wilhelm II wrote in the margins of the American note, "Utterly impertinent", "outrageous", and "this is the most insolent thing in tone and bearing that I have had to read since the Japanese note last August." Nevertheless, to keep America out of the war, in June the Kaiser was compelled to rescind unrestricted submarine warfare and require all passenger liners be left unmolested.

On 4 September 1915 Schwieger was back at sea with U-20, 85 nautical miles (157 km; 98 mi) off the Fastnet Rock in the south Irish Sea. This rock held one of the key navigational markers in the western ocean, the Fastnet Lighthouse, and any ships passing in and out of the Irish Sea would be within visual contact of it.

RMS Hesperian was beginning a run outward bound from Liverpool to Quebec and Montreal, with a general cargo, also doubling as a hospital ship, and carrying about 800 passengers when she was attacked and sunk by U-20 off the Fastnet. The History of the Great War: The Merchant Navy, Vol. II, by Hurd, reads:

"Only a few days before, Count Bernsdorff, the German Ambassador, had assured the United States government that passenger liners will not be sunk without warning and without ensuring the safety of the non-combatants aboard providing that the liners do not try to escape or offer resistance."

On 4 November 1916, U-20 grounded on the Danish coast south of Vrist, a little north of Thorsminde after suffering damage to its engines. Her crew attempted to destroy her with explosives the following day, succeeding, however, only in damaging the boat's bow (see picture) but making it effectively inoperative as a warship.^[4]

The U-20 remained on the beach until 1925 when the Danish government blew it up in a "spectacular explosion".^[5] The Danish navy removed the deck gun and made it unserviceable by cutting holes in vital parts. The gun was kept in the naval stores at Holmen in Copenhagen for almost 80 years.^[6] The conning tower was removed and placed on the front lawn of the local museum Strandingsmuseum St. George Thorsminde, where it still is today.^[5][7][8]

Novelist Clive Cussler claimed his National Underwater and Marine Agency (NUMA) located the remains of U-20 in 1984, about 400 yards from shore.^[9]

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