Unterseeboot 20 (U-20) has been the designation of two submarines of the German Navy.
On May 7, 1915, U-20 was patrolling off the southern coast of Ireland under the command of Kapitänleutnant Walther Schwieger. Three months earlier, on February 4, the Germans had established a submarine blockade around the UK and had declared any vessel in it a legitimate target.
At about 1:40pm Schweiger saw through his periscope a vessel approaching. From a distance of about 700 meters Schwieger noted four funnels and two masts, recognized RMS Lusitania, an element of the British Fleet Reserve, and fired a single torpedo. The torpedo struck on the starboard side, almost directly below the bridge. After the explosion of the torpedo, the liner was shattered by a second explosion (possibly caused by coal dust, possibly caused by war munitions in Lusitania's hold) so huge that Schwieger himself was surprised. Lusitania sank rapidly with the loss of nearly 1,200 lives, among them 128 Americans. The exact amount of time it took Lusitania to sink is not consistently reported, but was not more than 25 minutes.
Fifteen minutes after he had fired his torpedo, Kptlt. 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 and leave the area seawards. I couldn't have fired another torpedo into this mass of humans desperately trying to save themselves."
There was and is great controversy about the sinking, not only as to whether the rules of engagement permitted Schweiger to attack and whether Lusitania was smuggling contraband war materiel to England, but also over minutiae such as the number of torpedoes Schwieger fired. For a discussion of these issues, see RMS Lusitania.
She had numerous commanding officers over her eight-year career:
- February 1936 - September 1937: Kapitänleutnant Hans Eckermann
- October, 1937 - January, 1940: Kptlt. Karl-Heinz Moehle
- January, 1940 - April, 1940: Kptlt. Harro von Klot-Heydenfeldt
- April, 1940 - June, 1940: Oberleutnant zur See Hans-Jürgen Zetzsche
- June, 1940 - January, 1941: Oblt. Ottokar Paulshen
- January, 1941 - May, 1941: Kptlt. Herbert Schauenburg
- May, 1941 - December, 1941: Oblt. Wolfgang Sträter
- December, 1941 - March, 1942: Kptlt. Kurt Nölke
- March, 1942 - May, 1942: none
- May, 1942 - September, 1942: Oblt. Clemens Schöler
- September, 1942 - May, 1943: none
- May, 1943 - October, 1943: Kptlt. Clemens Schöler
- November, 1943 - September, 1944: Oblt. Karl Grafen
U-20 conducted 17 patrols, sinking 16 ships totalling 39,637 tons and damaging one more displacing 1,846 tons. On June 26, 1943, U-20 was attacked in the Black Sea by an escort with depth charges. Due to heavy damages the boat had to return to base. She did not suffer any casualties to her crew during her career. She was scuttled on September 10, 1944 off the coast of Turkey in the Black Sea.