After the scene in which the Americans blow up the radio shack on the German destroyer (chapter 14 on the DVD), they submerge rapidly to escape by diving under the keel of the destroyer. They watch the depth gauge and call out the depth in meters - 5 meters, 10 meters, 15 meters ... - and then we see the sub clear the keel of the ship comfortably.

We then see a view of the screws starting to turn as the diesel is started and you can clearly see that the sub is still on the surface.