http://mashable.com/2015/09/18/german-u-boat/#vRWio9gX8kks
Ned Beach (who wrote Run Silent, Run Deep) told this story on himself.
As part of training, his indoctrination to submarines after graduating in 1939 from USNA was a ride on an old S boat.
These were rather old subs, roughly equivalent to the Uboat in the photos, that were relegated to training on the east coast. On his first ride, he saw the bridge crew taking the boat out of New London, and then the boat dived.
Being a student, the bridge crew loaded him with their foul weather gear and he went to the engineroom. There, the gear was hung on a piece of wire, so it would dry. He was told to observe and stay out of the way.
Well, as the sub went deep, the wire sagged. This was because the hull compressed due to water pressure. This made the coats drop down and he couldn't see what was happening.
Without thinking, he tightened the wire to clear his field of vision. No problems. The boat carried on for about an hour.
When the sub started surfacing, the pressure hull began to expand as the water pressure lightened. This stretched the wire. Suddenly, the wire snapped and banged into the metal hull.
This was heard throughout the ship, "WHat was that! Are we flooding?" What broke?"
Getting no fast response from engineering, the captain yelled, "Blow all ballast! Surface Surface!"
Everyone was in adrenaline mode, thinking they were seconds from death.
And Ned knew he was going to get in a lot of trouble from tightening the drying line.
I was just going to post this story too, but I see you beat me to it. Super interesting!
The Daily Mail story about this says that nine of the 41 crew survived its sinking: http://www.dailymail.co.uk/news/article-3240463/Inside-killing-machine-ghostly-century-old-images-German-WWI-U-Boat-raised-depths-North-Sea.html (http://www.dailymail.co.uk/news/article-3240463/Inside-killing-machine-ghostly-century-old-images-German-WWI-U-Boat-raised-depths-North-Sea.html)