SM UB-18 was a German Type UB II submarine or U-boat in the German Imperial Navy () 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. The submarine sank 130 ships in 31 patrols for a total of making her the 13th most successful U-boat in both world wars. UB-18 was rammed by the trawler Ben Lawer and sunk in the English Channel at on 9 December 1917.