A well-judged performance by Kevin Costner brings drama to this actioner about the U.S. Coast Guard Service. The Guardian, directed by Andrew Davis, is a formulaic affair which blends deep-sea action with on-shore personal conflicts. Most A-list stars would have sleepwalked through the role of a heroic rescuer taking time out to teach some new recruits the ropes. But Costner evidently made a decision to bring something original to his character. He eschews both macho heroics and New Man sensitivity in favor of a quirky vulnerability. The film is frequently interesting as a result.

9/11 brought out a need for American audiences to see selfless heroes on the screen. Like firefighters, the bravery of rescue swimmers is beyond doubt. These are the men and women who dive out of helicopters into stormy seas and attach cables to those on sinking ships. Costner plays Randall, an old sea-hand with 200 saves behind him—as well as a broken marriage. To give himself some breathing room to work through his marital problems, he takes time out at a training school to break in some new recruits.

One of these is the arrogant Fischer (Ashton Kutcher), an Olympic-standard swimmer with a burning desire to upstage his tough teacher. The first hour of the film is a mixture of training scenes and personal affairs, as Randall puts the recruits through their paces. The second hour shows how antagonism between Randall and Fischer turns to friendship and respect after a shared secret. The finale is a dramatic rescue sequence involving both the men.

Directed by Andrew Davis (The Fugitive), The Guardian is a mixture of storm-at-sea movies like The Perfect Storm and camp-based dramas like A Few Good Men. The training scenes, which feature all manner of attempts to drown the recruits, are well-staged and enlivened by Costner’s grumpy humility. The rescues, which were staged in a water tank which was originally located in Louisiana (it was destroyed by Katrina, and had to be rebuilt), are good, and press all the right buttons.

But the personal scenes between the recruits almost manage to sink the movie. Kutcher’s romance with a teacher is a limp and uninvolving affair, while various other conflicts and rivalries are too by-the-book to care about. The drama is made worse because Kutcher has to play arrogant and mean for the first half. He’s simply not very convincing at being bad, and only seems to find his feet when the decks have been cleared and he’s been primed for some bona–fide heroics.

It’s left to Costner to keep the film afloat, and he copes admirably. Even though he’s bogged down by a script that’s often rote, his gestures and smiles bring a real humanity to his part. He’s tough on his recruits, but he’s never a Full Metal Jacket martinet, and there’s something intriguing about the humble way he keeps order. The actor also makes Randall’s scenes with his estranged wife touching.

Costner’s subtlety makes The Guardian eminently watchable. If only he would use his skills to make more films like the superlative Open Range instead.