Von Trotha was born in Kiel on 7 August 1916 and entered the Kriegsmarine twenty years later with the intake the navy nicknamed the Olympia Crew, after the Berlin games of that summer. His apprenticeship was the standard one for an officer of his generation: the light cruiser Königsberg, then the old battleship Schleswig-Holstein, freshly converted to a cadet training ship and running long instructional cruises to South America and around Africa. That same ship opened fire on the Polish garrison at Westerplatte at 04:47 on 1 September 1939 and fired the first shots of the war. Von Trotha moved to submarines in 1941. He was given U-733 in November 1942 and took her on no war patrols at all; when U-745 was commissioned on 19 June 1943, built by Schichau-Werke in Danzig, he took command and kept it for every day of her existence.

U-745 made four patrols, 114 days at sea in total, and sank two vessels between them. The first was the Soviet minesweeping trawler T-45 Antikajnen, 140 tons, on 26 August 1944. The second, on 11 January 1945, had a stranger history than most warships accumulate in a century. She had been launched at Geestemünde on 31 October 1917 as SMS M59, a German minesweeper; sold to Lithuania in 1927 and renamed Prezidentas Smetona after the country's first president, she became the pride of Lithuania's very small navy. The Soviets took her in 1940 and renamed her twice more — Pirmūnas, then Korall — before converting her back to a minesweeper and renaming her a fifth time, to T-33, on 29 August 1944. She went down off Helsinki under that final designation, five months later, with six hundred tons and a long list of former identities behind her. German records credit U-745 with the kill, though whether it was her torpedo, a mine, or another boat has never been settled.

The day after T-33 sank, on 12 January 1945, two Finnish minelayers went out into the water south of Hanko and laid a barrage designated Vantaa 3. Finland had spent three years fighting the Soviet Union alongside Germany. The armistice of September 1944 required the Finns to expel their former allies from their territory, and so a Finnish crew now spent a winter afternoon sowing mines meant specifically for German submarines — boats that a season earlier had shared their ports and their charts. It took nineteen days. Wherever U-745 was going on 31 January 1945, her course crossed that barrage, and the war she had been fighting ended for her in the space of a few seconds.

There is a detail in U-745's record that reads oddly against the rest of the U-boat service. Most boats bled steadily — men lost overboard, killed by strafing aircraft, injured in accidents, invalided out. U-745 had lost nobody. Through eighteen months of commissioning, training, and four operational patrols, not one of her crew was killed. She left Libau, now Liepāja in Latvia, on 24 December 1944 for what turned out to be her final run, and simply stopped answering. Forty-eight men, unhurt for the whole war, died together in one instant of that January afternoon. Von Trotha's family got a grave. Forty-seven other families got nothing but a date and a stretch of open water.

Finding a 67-metre object on a seabed as cluttered as the Gulf of Finland is not a weekend project. The Finnish wreck-diving team Badewanne, who have spent decades documenting the extraordinary density of shipwrecks in these waters, searched for U-745 for roughly ten years before locating her in late 2012, south of Hanko. On the way they also found U-676, another Type VIIC, killed by the same Finnish barrage on 12 February 1945 with all fifty-seven aboard. The Baltic is cold, dark, brackish, and almost free of shipworm, so wrecks here do not rot the way they do in warmer seas — they sit on the bottom looking startlingly like ships. U-745 is a war grave, and the divers who visit her stay outside the hull.