A German Type UB II submarine, ‘’UB-18’’ had a displacement of when at the surface and while submerged. They had a length overall of, a beam of, and a draught of. The submarine was powered by two Daimler six-cylinder four-stroke diesel engines each producing , two Siemens-Schuckertelectric motors producing, and one propeller shaft. She had a dive time of 45 seconds and was capable of operating at a depth of. The submarine had a maximum surface speed of and a submerged speed of. When submerged, she could operate for at ; when surfaced she could travel at. UB-18 was fitted with two torpedo tubes in the bow, four torpedoes, and one 5 cm SK L/40 gun| Tk L/40 deck gun. Her complement was twenty-three crew members.
Service history
Franz Wäger took command of UB-18 upon commissioning on 11 December 1915. Wäger handed over command to Oblt.z.S. Otto Steinbrinck, who sailed her to Zeebrugge, arriving on 16 February, the first U-boat of the type to be based there.
1st War Patrol
At the end of February 1916, UB-18 left Zeebrugge for the approaches to Le Havre. On 26 February she launched a torpedo hitting the French steamer, whose sinking was not observed. The attack on the was more successful, sinking the 20-year-old ship of, killing 18 crew members. UB-18 returned to base arriving there 29 February 1916.
2nd War Patrol
On 4 March 1916UB-18 provided flank cover for a German fleet sortie against the English east coast.
3rd War Patrol
From 7–11 March 1916, UB-18 operated against Allied shipping off Boulogne and Le Havre. On 8 March, she sunk a British steamer,, and the following day, a Norwegian freighter, the Silius, and a French steamer,, fell victims to UB-18s torpedoes.
4th War Patrol
On 21 March 1916, UB-18 left Zeebrugge again for the Le Havre area, where she successfully attacked ships lying in the roads. Two ships, the British freighter, and the Norwegian steamer were hit by torpedoes and sank. The two reloads did not show any hits. UB-18 returned to Zeebrugge, arriving on 29 March 1916. That day, the Flanders Flotilla was formed, and Steinbrinck was awarded the coveted Pour le Mérite order.
Loss
Sailing on her last patrol, she was seen off Start Point, Devon by U 84 on 4 December 1917, bound for the Western Approaches. Early on the morning of9 December she inadvertently surfaced close to the trawler Ben Lawer, which was escorting a coal convoy. The trawler immediately rammed her just aft of the conning tower, sinking her; there were no survivors. The impact was substantial, with the Ben Lawer so badly damaged that she only just made port.
