UB-85 was a Type UB III submarine, the most common German coastal U-boat design of the late First World War. She was ordered on 23 September 1916, built at the AG Weser shipyard in Bremen, launched on 26 October 1917, and commissioned on 24 November 1917 under Krech's command. Like all Type UB IIIs, she carried ten torpedoes and one 8.8 cm deck gun. She displaced 516 tonnes surfaced and 647 tonnes submerged. Her crew was three officers and 31 men, sometimes more. Her cruising range was a respectable 8,180 nautical miles. She could make 13.4 knots on the surface and 7.5 knots when submerged. She was, in other words, a standard war-built submarine of her class, indistinguishable on paper from the dozens of other UB IIIs whose patrols ended in less mysterious ways.

On 30 April 1918, UB-85 was on her second war patrol when she was detected by HM Drifter Coreopsis II off the Northern Irish coast. Drifters were small herring-fishing vessels requisitioned for war work, slow and lightly armed, but their job was to lay anti-submarine nets and provide flotillas of eyes on the surface. UB-85 attempted to evade attack but took on water through a hatch that, by the official German account during interrogation, had been left partly open. Forced to the surface and unable to dive again, the U-boat was abandoned by her crew while under fire. All 34 men were rescued and taken as prisoners of war. UB-85 sank shortly afterwards. The capture was a small but real propaganda victory for the Royal Navy in the difficult last year of the war.

What happened next belongs to history and to folklore in roughly equal measure. The official British account of the interrogation noted that Krech had given a strange explanation for his vessel being unable to submerge. According to the story, which was repeated in British newspapers, UB-85 had surfaced the night before to recharge her batteries in calm sea conditions. A large creature, described as a strange beast with eyes and small horns, climbed partway onto the foredeck. The crew opened fire with sidearms; the beast eventually slipped back into the water; but the boat's forward deck and one of its hatches were damaged sufficiently that diving was no longer safe. There are reasons to be sceptical. The story would have made a perfect excuse for surrendering an intact U-boat. The British interrogation officers may have transcribed or even embellished a sailor's grim joke. Sea-monster stories have always travelled well. And yet the question stands: a perfectly working German submarine surrendered intact to a fishing drifter, with all hands rescued, and her captain's stated explanation involved a creature from the deep. Submariners do not surrender lightly. Something happened. The official explanation was implausible. The unofficial explanation was impossible. Most likely the truth lies somewhere between mechanical failure and human exhaustion in the last desperate spring of the war.

In October 2016, engineers laying the Western HVDC Link, an undersea cable connecting Scotland with Wales, encountered the almost intact wreck of a Type UB III submarine on the seabed off the Galloway coast. Marine archaeologist Dr Innes McCartney identified it tentatively as either UB-85 or her sister UB-82, although precise identification remained difficult without a dive. McCartney told the BBC at the time that they were certainly closer to solving the so-called mystery of UB-85 and the reason behind its sinking, whether common mechanical failure or something less easily explained. He chose his words carefully. The cable engineers had no particular interest in cryptozoology. They had a submarine to work around and a contract schedule to keep. UB-85 had been on the bottom of the Irish Sea for 98 years, and she remains there, one of thousands of objects laid down by the First World War and then quietly absorbed by the sea floor.