SM UC-18 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 29 August 1915 and was launched on 4 March 1916. She was commissioned into the German Imperial Navy on 15 August 1916 as SM UC-18. In 6 patrols UC-18 was credited with sinking 34 ships, either by torpedo or by mines laid. UC-18 was sunk by the British Q ship HMS Lady Olive on 19 February 1917.