[Sailor Steve]

A few u-boats which were snorkeling in less than perfect seas had to emergency surface when the snorkel dipped below the waves. There was a float to keep water from coming into the engines, but the engines sucked the air out so fast that people were already struggling to breath when they broke surface and the fans kicked in.

Standard procedure was to shut the engines down and switch to electrics as soon as the dive was called. The 'Christmas Tree', the board of lights showing which hatches and vents were still open, had to be all green before they even began flooding.