Submarine warfare so lends itself to filmmaking that even a bad sub movie is likely to be pretty good. "Das Boot," a new U-boat epic from Germany, is so good it's bad. Wolfgang Petersen's film is based on the novel of the same title by Lothar-Gunther Bucheim, which complements and very nearly equals The Cruel Sea by Nicholas Monsarrat in the literature of naval warfare. Like no one before him, director Petersen has captured the grimy and horrific details of U-boat life, but because of an almost total lack of feel for the sea, ships and seamen, he has wasted a chance to produce a classic. When the action takes place inside the boat, as most of it does over the 21/2-hour running time, the setting and casting and camerawork are so superb that one almost has a sense of having signed on for the patrol. But the mood is dissipated by lapses of continuity and by bizarre behavior such as never was permitted in the Kriegsmarine or any other submarine service. Submariners did not scream and yell and thrash around wildly while under attack, nor would the crewmen bully one of their fellows by pawing through his seabag and commenting obscenely on pictures of his women. They lived or died by virtue of unnatural calm and reflexive responses, largely controlled by hand signals and instilled by endless drill; and service in an unterseeboot was so crowded, nastily intimate and interdependent that iron custom required every man to respect the privacy and dignity of his mates. Any U-boat that went down like Petersen's never would have come up. The inadequacy of the English subtitles was apparent even to a viewer who has only a few words of German. A seatmate who is fluent in the language, including military idioms, found the actual dialogue to be such a strange mixture of formal, gutter, archaic and anachronistic Deutsch that she wondered if the cast were Scandinavian. When Petersen surfaces his sub, the whole show goes to hell. It has been a long time since such poorly made and handled models were acceptable in even low-budget flicks. He could have shot the film in black-and- white, which would have been more appropriate, and spent the money he saved on realistic burning tankers and onrushing destroyers. Scenes on the bridge are so obviously sound-stage mockups one can all but see the buckets of water being flung. For all the film's flaws, the casting and costuming, the cinematography, choreography, interior sets and shore locations are so fine it's hard to believe anyone who got so much so right could get the rest so wrong. Making World War II movies in Germany no doubt is a delicate matter, and Petersen is almost servile in assuring us that he hates Nazis, as did most German submariners. Yet they followed the Fuehrer to the death: Some 30,000 of the 40,000 who served in U-boats died; with the ever-younger replacements it became a children's crusade. Bucheim, an artist and war correspondent, explained in his novel how such half-hearted yet full-bodied devotion was possible, but few hints of that motivation made it into the movie. He also took fascinating photographs of submarines in action, which were published in U-Boat War, a nonfiction work whose images so captured Petersen that he virtually used it as his shooting script. Too bad he didn't take time to read the books.

DAS BOOT -- At the K-B Janus and Outer Circle.