I just had an unusual incident involving a C&D Class Destroyer too.
I was cruising around at 256tc, submerged at periscope depth between the Shetland Islands and Aberdean in my type IIA in 1939. I suddenly get "warship detected close range" from the hydrophone operator. I switched to the nav map and there he was, right on me! Then there I heard explosions so I went to external camera to see what was going on and found the C&D about 500m in front of me at a 90 AOB. The explosions appeared like DC explosions about 100m behind my sub. I think this was some kind of TC mess up because there's no way he could have circled around that fast.
Anyway, I had a perfect torpedo shot and as the water was too shallow to allow me a good chance to escape I gave the C&D both barrels. The fish were set to impact trigger running 1.5m metres deep. When the first fish hit it blew the destroyer out of the water and broke its back. I didn't notice the second explosion so the second fish either missed or ran beneath the ship when it was momentarily out of the water.
Anyway, it was the most violent explosion I've ever seen in the game and it just didn't quite seem "right".
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Sexycandyfox