A true story worth telling, this movie suffers heavily from contrived dialog which was obviously written by someone unfamilar with the Navy. It's a classic example of writers who have learned most of what they think they know about their subject matter from watching previous movies which were just as likely written by still other writers who learned from watching still earlier movies, ad infinitum. The use of an Iowa-class battleship to portray an obsolescent pre-war heavy cruiser less than one-third its size didn't help, either.
One technical point: speaking as a former submariner and current submarine museum director, speed was always generally regarded a significant defense to submarine attack, and given the technology available at the time it was just plain bad luck as much as anything else that the Japanese were actually able to hit the INDIANAPOLIS. Note also that the submarine had to fire a total of six torpedoes to achieve two hits.
One last point: speaking as the survivor of a vicious wild-animal attack, I can attest that the fear of it is infinitely worse than its physical reality, and I could easily come up with a long list of worse ways to go - surely one would suffer worse from dehydration and exposure, to say nothing of what the medical profession is capable of doing to you once you get to a hospital.
***SPOILER ALERT *** Incidentally, McVay never recovered from the sinking. He committed suicide in 1968. In 2000 the United States Congress passed and the President signed a formal resolution exonerating him from blame for the sinking.