SM UB-85 was a Type UB III U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. Ordered on 23 September 1916, the U-boat was built at the AG Weser shipyard in Bremen and commissioned on 24 November 1917, under the command of Kapitänleutnant Günther Krech.

SM UB-85 was built by AG Weser of Bremen and following just under a year of construction, launched at Bremen on 26 October 1917, and was commissioned later that same year. Like all Type UB III submarines, UB-85 carried 10 torpedoes and was armed with a 8.8 cm (3.46 in) deck gun. UB-85 would carry a crew of up to 3 officers and 31 men and had a cruising range of 8,180 nautical miles (15,150 km; 9,410 mi). UB-85 had a displacement of 516 t (508 long tons) while surfaced and 647 t (637 long tons) when submerged. Her engines enabled her to travel at 13.4 knots (24.8 km/h; 15.4 mph) when surfaced and 7.5 knots (13.9 km/h; 8.6 mph) when submerged.

On her second patrol, she was picked up by HM Drifter Coreopsis II off the coast of Belfast, Northern Ireland on 30 April 1918, after she was partly flooded through a semi-open hatch while trying to evade attack by the British vessel. The ingress of water could not be controlled, since cables for a heater in the officers' compartment had previously been laid through a watertight door, by order of Kapt. Krech. The submarine was forced to surface and was abandoned by her crew while under fire. No casualties occurred amongst the 34 crew who were taken as prisoners of war.

Under interrogation, the captain is reported to have said that the submarine had surfaced the night before to recharge the batteries and had been attacked by a large sea creature, a "strange beast" that rose out of the deep and damaged the vessel, leaving it unable to submerge. The crew had fired their sidearms at the creature.

Engineers working on an electricity cable, the Western HVDC Link, discovered the almost intact wreck of a UB-III class submarine, believed to be either UB-85 or UB-82, lying off the Galloway coast in October 2016. Dr Innes McCartney who identified the wreck said: "We are certainly closer to solving the so-called mystery of UB-85 and the reason behind its sinking - whether common mechanical failure or something that is less easily explained."

• SM U-28 (Germany)

• Helgason, Guðmundur. "WWI U-boats: UB 85". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net.