U-777 was a late-war Type VIIC, the workhorse class that built the U-boat arm. She measured 67 meters long, displaced 769 tonnes surfaced and 871 submerged, and was powered by twin Germaniawerft diesels above water and twin Garbe-Lahmeyer electric motors below. Her topside armament reflected how dangerous Allied air power had become by 1944: not just the standard 8.8 cm deck gun, but a 3.7 cm Flak M42 and two twin 2 cm anti-aircraft mounts crowding the rebuilt conning tower. She carried five torpedo tubes - four forward, one aft - and a complement of fourteen torpedoes for them. She was, in every measurable way, exactly the kind of boat the Allies were now sinking faster than Germany could build.

She had only one commanding officer: Oberleutnant zur See Gunter Ruperti, who took her from her commissioning on 9 May 1944 straight into training. The 31st U-boat Flotilla was based in the Baltic, where the relatively safe waters allowed new crews to learn the dives, the trims, the surface attack patterns that they would, in theory, need on patrol. There was an unusual statistic associated with U-777 during this period: many other training boats lost men to accidents, disease, electrical fires, or carbon monoxide. U-777 lost none. Her crew, for those five months, was lucky. Then their luck ran out at her mooring.

By the autumn of 1944, the great fortified U-boat base at Wilhelmshaven had become one of the most heavily bombed targets in the Reich. RAF Bomber Command and the US Eighth Air Force took turns at it, working through the bunker pens and the surrounding docks. U-777's records simply note that she was destroyed at 20:02 hours on the night of 15-16 October 1944 during a British air raid. One crewman died. The boat was beyond salvage. She was raised on 22 October 1944, classified as a constructive total loss, and eventually scuttled on 5 May 1945 at Wilhelmshaven. By the time the rubble cleared from her berth, the war had less than seven months to run, and the U-boat arm's death rate had climbed to the worst it would ever be.

Gunter Ruperti's story did not end at Wilhelmshaven. Promoted to Kapitanleutnant, he took over a new boat - the Type XXI U-3039 - in March 1945, only about five months after U-777's destruction. The Type XXI was Germany's late-war wonder weapon, a true submarine designed to live underwater rather than just dive briefly, with batteries powerful enough to outrun a destroyer below the surface and a streamlined hull that anticipated nearly every postwar submarine design. He commanded her until the war ended in May. Ruperti was one of those U-boat officers who survived the meat grinder, and his career bridged the entire arc of German submarine technology - from the obsolete Type VIIC that died at her mooring to the revolutionary Type XXI that came too late. U-777, in that sense, was a way station: the boat between his training career and his final command, sunk before she could do anything but exist.