SM UB-27 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 10 February 1916. She was commissioned into the German Imperial Navy on 23 February 1916 as SM UB-27. UB-27 sank 13 ships in 17 patrols for a total of . UB-27 disappeared after 22 July 1917. HMS Halcyon reported ramming and depth charging a U-boat on 29 July 1917. A postwar German study concluded that it was possible that Halcyon sank UB-27 at .