Pretty standard movie for its time, although one of the few that wasn't based off a historic battle or something along that line. we do get to see it in colour which is nice, and we are treated with the same actors that every war movie of the time starred. The sets are nice, maybe a bit too clean and layed back for a fighting ship however. The destroyer is all filmed aboard a real destroyer off Hawaii, and I'm sure the U-boat is portrayed by a mock up, used for surface shots only, while the underwater model they used is very convincing, and for the time one of the best special effects in a war movie I've seen. In inside of the U-boat is quite obviously not a real one, and although I haven't been able to find information on it, it's probably a mock up or a more modern American sub. The acting and script are typical of the era, and so is the comradeship that is shown between the two commanders. The underwater explosions simulating death chargers are very good, as are the on deck explosions in the final duel. But the real depth charges going off from the on deck view are simply amazing, and we see the same explosions today in U-571, which is decades ahead in special effects and the likes. It is a good naval film, a theatre of war not covered well, simply because of the need for a huge budget for both a ship and a crapload of CGI needed to make it. It's among the better ones however, not as modern but better done than Pearl Harbor, although it does lag behind almost all of the great submarine movies, notably Das Boot, which is in an entirely different ball park. However good classic war flick, pretty casual now, but a big step forward in its time, and it still shines today.