I'm a former U.S. Navy submariner so I detected some errors in submarine operations and procedures...no boatswains mates or boatswains whistles on subs...it's "Dive, Dive" and "Surface, Surface, Surface" when ordering these operations with accompanying equal number of claxon preparations.  Topside vents don't spray when surfacing since they're shut tight to allow air to blow ballast out the flood ports in the bottom of the boat.  All that aside, however, the book was a great adventure and I enjoyed it very much.