From the book U-boat Ace

       Early morning, 4 February 1941. The harbor in Lorient is dark. Tied to the shore with heavy chains is an old sailing ship the "Ysere". She has no mast, no crew, and no watch. The Ysere is dead, but they have dressed her up to serve as a floating pier.

        Tied to this pier is U-43. (Wolfgang Luth) There are six men on board. The watch officer who sits in the petty officers mess reading. Every hour he gets up and makes a round of the boat. The other men in the watch section are in their bunks except one. A single watchstander must remain topside at all times. It's boring, nothing to see or do. The man crosses the gangplank from U-43 to the Ysere.

         The rest of the officers and crew are ashore. They have been told that U-43 will sail at dawn, and in the few hours they have left they intend to celebrate.

         The man standing watch does not know where U-43 is going. He's cold because it's February.

         He walks through silence broken only by the occasional rumbling of an engine, or the distant laughter of drunken men. Then he hears a sudden loud "crack". It is a pistol shot. The sentry stops in his tracks, his rifle ready. The sound echos and then silence again. He turns and peers into the darkness, puzzled. He has heard this sound before but, can not remember where.

        A whisper from below, an almost silent bubbling sound, like the foam in a beer, persuades him to look down. And then he knows instinctively what has happened: one of U-43's mooring lines has snapped in two. At the very moment the sentry see's something else-a gurgle of swirling white water where U-43's after torpedo room hatch had been, a flash of red and white as her ensign goes under. The entire after section of U-43 disappearing in the murky waters of her berth.

        To his amazenment the boat he is supposed to watch is sinking, fast, and as he gapes another line parts with a creak and a crack. The sentry runs stumbling down the gangplank between the Ysere and U-43, jumps and falls onto the sloping deck of his dying boat, clambers up the ladder and into her tower. Then he begins to shout, hoping they won't shoot him for what has happened....

       They raised U-43 with cranes in mid-afternoon. Luth and Petersen (3rd WO) had been hanging around for hours, and when they were finally allowed to go below there was nothing but water, with charts, tin cans, coffee beans and clothing all floating in a greasy oil slick. The sight, said Petersen was "indescribable", and prospects for him and Luth even more dismal. Having your boat sink at sea was one thing; allowing it to sink in port, under guard, moored to a tender, was another.....

       It took a few days to figure out exactly what happened. The problem concerned valves. "Someone" had fooled around with valves and vents in such a way that water started to slowly seep into the bilges. The leak was so slow that it went unnoticed, but the boat had probably taken on alot of water before the crew even went ashore that night...

        Individual punishments are not discussed but Donitz made half the crew stay in Lorient and clean up the boat and the other half were sent back to Germany for more training.

         It took three months to clean up U-43, and it was never the same boat after that. They replaced almost everything except the batteries and they never held a full charge after the sinking. Luth found himself at sea more then once with his electrical power down to a trickle because of that night in Lorient.