Flender-Werke laid down U-318's keel on 14 October 1942 in Lubeck - the Hanseatic League city on the Baltic, famous for its medieval brick churches and its marzipan. The yard had built ships for centuries before it built submarines. By autumn 1942 the Kriegsmarine was ordering hundreds of Type VIIs across every yard in northern Germany and Nazi-occupied Europe; the Allies were already breaking Enigma and reading German naval traffic in near-real-time. Oberleutnant zur See Josef Will took command at her commissioning on 13 November 1943. She trained briefly with the 4th U-boat Flotilla and then began the strange, restless life that characterised late-war German submarines: a constant pattern of short voyages between Norwegian fjord bases, never longer than 32 days, rarely finding targets, always at risk from the air.

Her bases form a map of Nazi-held Norway from south to north: Egersund near the southwestern tip, Bergen and Kristiansand on the southern coast, Arendal and Trondheim further north, Bogenbucht and Kilbotn and Harstad in the high Arctic. Narvik, on the Ofotfjord above the Arctic Circle, was the last and northernmost - the iron ore port whose 1940 capture and recapture had been one of the bloodier campaigns of the early war. By 1944 Narvik was a U-boat base, sheltered by mountains, locked in winter darkness from November to January. U-318 worked these waters with the 11th Flotilla, then transferred to the 13th, then the 14th. Six patrols, two wolfpacks - Eisenhart 3 and Schill 3 among the names - and never a confirmed kill.

The wolfpack tactic had been Karl Donitz's signature innovation - U-boats coordinated by radio into ambushes on Atlantic convoys, attacking together by night to overwhelm escort screens. In 1940-42 it had nearly won the war. By 1944, the wolfpacks were dying. Allied direction-finding could pinpoint a U-boat the moment it transmitted. Allied escorts had radar and sonar that could find a submerged boat in any weather. Allied air cover meant any U-boat that surfaced - and they all had to surface to charge their batteries - was visible from twenty miles away. The wolfpacks U-318 joined did not score the kills Donitz needed. They mostly just lost boats.

On 9 May 1945, the day after Germany's formal surrender, U-318 hoisted a white flag in Narvik harbour. The town that had been fought over so bitterly five years before was the last German naval base in Norway to capitulate. Will and his crew were handed to the Royal Navy. The boat herself was moved south through the inland Skjomenfjord, then across the North Sea to Loch Eriboll in Scotland, arriving on 19 May. Like dozens of her sisters she was moved on to Loch Ryan, the principal Operation Deadlight gathering point, to wait for the scuttling that would erase the U-boat fleet from existence.

Most of the Deadlight boats were simply sunk by gunfire or by foundering under tow. A few were used for something more practical: Allied gunnery and torpedo practice. U-318 was sunk on 21 December 1945 north of Northern Ireland as a Royal Navy target ship. Live torpedoes were fired into her hull. Naval gunfire put rounds through her conning tower. The submariners who had built and crewed these boats - intricate, expensive machines of war that had taken Germany years to design - watched, from their internment camps, as the Allies dismantled them at the leisurely pace of training exercises. U-318 went down to mark a target. She lies somewhere northwest of Ireland, a single point in the dark mathematics of the post-war Atlantic.