I seem to recall in the book the survivors are left to die but are rescued by an American boat that responded to a distress radio call. It's been a while and Ned Beach's
Dust on the Sea was the better book (IMHO) but was never made into a film. Obviously the producers opted for the "Once out of the hole, our hero..." dramatic license popular in serial dramas of the time.
Complaints about "realism" or lack thereof in film or TV are always so amusing.
As for ramming, on 10 September 1941
HMCS Moose Jaw, Lt Fred Grubb hit
U-501 broadside to broadside in heavy seas and the boat's captain, KK Hugo Forester took the opportunity to jump from his conning tower onto
Moose Jaw's deck. A rather interesting method of surrendering.
Moose Jaw's 4" gun had jammed.
Here's a link:
U-501
The book
Canadian Naval Chronicles (Fraser McKee and Robert Darlington) goes into more details about this unusual action than the website.