SM UB-18 was a German Type UB II submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 30 April 1915 and launched on 21 August 1915. She was commissioned into the German Imperial Navy on 11 December 1915 as SM UB-18.[Note 1] The submarine sank 126 ships in 31 patrols for a total of 129,782 gross register tons (GRT)[3] making her the 13th most successful U-boat in both world wars.[4] UB-18 was rammed by the trawler Ben Lawer and sunk in the English Channel at 49°17′N 5°47′W﻿ / ﻿49.283°N 5.783°W﻿ / 49.283; -5.783Coordinates: 49°17′N 5°47′W﻿ / ﻿49.283°N 5.783°W﻿ / 49.283; -5.783 on 9 December 1917.[2]