High Quality Content by WIKIPEDIA articles! SM U-20 was a German Type U 19 U-boat built for service in the Kaiserliche Marine. 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. The 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.