Take note of the tilt

[Blacklight]

I'd say.. look at the immense speed the Uboat is travelling and the torpedos that zips out is going a crapload faster than it. I have a feeling that it has something to do with the torpedo hitting the boat at a few hundred mph ! I think it's the game's physics system trying to deal with that.

So what control surface would allow the sub to barrel roll in the water like that? ...I mean that we would have any control of?

I have no clue. I've been trying to barrel roll my Uboat ever since I saw this video a long time back with no success. I suspect that the video was either edited at that part to make it look like it's spinning, or he did an out of control crash dive somehow that spiriled his sub into the depths.