I once dived a wreck that we'd only ever seen in really poor visibility due to its proximity to the mouth of the Tyne only to find the water crystal clear and the whole ship visible from one end to the other. There in the stern deck was a perfectly circular hole about ten feet across and in the bottom was a 20mm, Oerlikon AA cannon sat bolt upright. Its circular mounting plate and the heavy gun had literally dropped through the rust-thinned deck.
Two minutes later I was stood, finger on the trigger, blazing away at imaginary, HE111s through the hole above - you can blame the old nitrogen narcosis for that.
I always wonder whether these ships sank on a calm, moonlit night, in bright sunshine or in the middle of a storm. I wonder who was lost and who got off and what it must have been like as the ship was rent by a torpedo or mine explosion and what the scene on board must have been like as she settled and sank.
