U-97 was a Type U 93 ocean-going submarine, the successor to the slightly shorter Type U 87 design. She displaced 838 tonnes surfaced and a thousand submerged, ran 71.55 metres long with a pressure hull of 56.05 metres inside that, carried a beam of 6.30 metres and a draught of just under four. Two diesel engines of 2,300 PS each drove her on the surface; two 1,200-PS electric motors took over below. Her absolute test depth was a modest 50 metres - shallow by later standards - and she carried six 50-centimetre torpedo tubes, four bow and two stern, with twelve to sixteen torpedoes stowed for them. A 10.5-cm SK L/45 deck gun stood forward of the conning tower. Thirty-six men crewed her: thirty-two ratings and four officers, squeezed into a steel cylinder that smelled permanently of diesel, sweat, and seawater.

U-97 was not a famous boat. She does not carry a Weddigen or a Steinbrinck legend; the Wikipedia stub of her career runs to a handful of paragraphs. But she lived in the densest naval campaign the world had ever seen. Of the 329 U-boats Germany sent to sea between 1914 and 1918, roughly half were lost - to mines, depth charges, surface gunnery, ramming, accident, and the simple wearing out of crews and metal. The surface speed of these boats was a respectable 16.8 knots; submerged, they could only crawl at 8.6 knots for less than ten hours before their batteries ran flat. Almost every torpedo attack the U-boat arm made on Allied shipping took place on the surface, at night, eyes pressed to a wet bridge coaming. U-97 was one of those boats - faceless in the histories, dangerous in the moment, ordinary in her crew.

What killed U-97 was not a destroyer or a Q-ship but the surrender itself. The armistice of 11 November 1918 required Germany to deliver her surviving U-boats to the Allies. Crews were exhausted, supplies thin, and the boats themselves were tired metal. U-97 had taken part in naval warfare and in the First Battle of the Atlantic; she was on her way to internment when she sank by accident on the surface, somewhere in the shallow southern North Sea. There is no recorded heroism here and no recorded outrage - just the unromantic fact that a steel cylinder full of valves and pipes, run hard for a year and a half, gave up on the wrong day. Her position is reported around 53.42 N, 3.17 E, in the same approaches where Otto Weddigen's U-9 had ambushed three British cruisers four years earlier.

Look at the spec sheet again, and the casualty math starts to register. U-97 could travel 8,290 nautical miles on the surface at 8 knots; she could not go 50 miles submerged without recharging. Her men slept in folding cots between the torpedo tubes. The skipper had a curtained alcove and the chief engineer had a stool. Ventilating a dive in winter meant living in a slick of condensation on every cold metal surface. The 8.8-cm deck gun was the boat's main weapon against unarmed merchantmen - torpedoes were precious. Whatever the strategic argument about the unrestricted U-boat campaign and its consequences (and the argument is real and not finished), the people inside the boats were sailors doing dangerous and unforgiving work in equipment that was perpetually a little too small for the sea around it.

U-97's wreck, if it remains identifiable on the sandy seabed of the southern North Sea, sits a few hundred metres down with the other quiet ironwork of two world wars. Sport divers do not visit her; the depth, the visibility, and the obscurity all argue against it. She is one of thousands of small graves on a chart that, from cruising altitude, looks like uninterrupted grey water. The next time you fly the Texel approach in clear weather and see the long shallow shelf out toward the Dogger, remember: every kilometre under your wing has a U-boat or a trawler or a tanker in it. U-97 is one of the unflashy ones, ended not in battle but in the indifferent paperwork of an empire's collapse.