In sports and the military, “professionalism” describes people who go about their work with a calm, dispassionate efficiency — no fuss, no panic when things go wrong, few mistakes, little attention paid to the odds, the chance for glory.

You can apply that word to movie actors, too. The great cast of character actors of “Phantom,” a solid Cold War-era submarine thriller of modest ambitions, never reveals that this isn’t “The Hunt for Red October” or “K-19: The Widowmaker.”

Ed Harris, William Fichtner, David Duchovny and Co. show up, hit their marks, give their lines some punch and play the heck out of this B picture, which could easily have been just a prop (a submarine) in search of a movie.

Writer-director Todd Robinson (he scripted “White Squall”) has cooked up an alternative bit of Cold War mythology. In 1968, a tense time when U.S. and Soviet subs were tangling and occasionally sinking, a Soviet sub went missing. Here’s a far-fetched explanation.

Harris plays the retiring Soviet captain taking the B-67 out to sea on one last cruise before they sell her to the Chinese and put him out to pasture.

Does he believe in omens? His hastily assembled crew drops stuff while they’re frantically loading the boat. Things break. Oh, and his commanding officer (Lance Henriksen, another old pro) shoots himself as the B-67 clears the harbor.

On board is a nuclear-armed missile, some sort of experimental gadget and a couple of heavy-handed security guys, led by Bruni (Duchovny).

Nobody feigns an accent. They just go about the business of putting an aged, crowded killing machine through its paces en route to the Pacific, where nerves, loyalties and history will be put to the test.

Robinson manages some suspense, but the thriller’s ticking clock is a weak one. He’s sloppy at solving script problems, giving a character in the sub claustrophobia (!?) so that another character must handle a difficult task.

But the cast never lets on that this alternative history isn’t the most dazzling riff on the Soviet-era “Silent Service.”