I was starting my second patrol from Kiel. In free cam mode, moving around admiring my new emblem while my boat's slowly moving forward at 4/5 knots. Suddenly I press "p" (didn't really know what it did back then). Before I know it I get screeching noises from my boat and my crew trying to raise hell with damage reports all around.
Ohhh so it dives to periscope depth with "p"? Lesson learnt at the cost of 45 lives.