My grandfather was a petty officer on the HMS Danae during WW1. He died 17 years ago. I heard a story from my cousin recently that was told him by my grandfather, as follows, and I am trying to investigate it. Any help gratefully received.
They came across a "ghost" ship, and eventually found a single survivor, hiding behind one of the boilers in the engine room. His story was that he was the only survivor after his ship had been attacked and stopped by a uboat. The uboat had machine gunned the decks.
Some months later the Danae forced a uboat to the surface with depth charges, and it was noted to be the same uboat from the episode with the ghost ship. My grandfather was ordered to stand to attention, and hold a salute, as the uboat sailors were machine gunned. In retaliation.
An interesting story, but I can't find any confirmation anywhere. I believe he only served on the Danae.