Tom Hanks shows what a commanding actor he can be from the first taut combat sequence of “Greyhound,” when the title warship, leading a convoy through the North Atlantic in the early months of World War II, spies a U-boat speeding toward it from a dozen miles away. As the German sub approaches, we hear a lot of rapid-fire military and navigational jargon shooting back and forth between the sailors (“Hydrophone effects slow rev, sounds like 60 RPM, sir!”). The action builds, but what lends the scene emotion is the play of aggression and anxiety just beneath Hanks’ fixed grimace. He’s the ship’s captain, Commander Ernest Krause, a stalwart and decisive leader of men, but the primal fear of battle is etched onto his face. As war films have grown more sophisticated in their realism, it’s not just the ricocheting din of bullet clatter or the dirt-flying dizziness of battle that can hit the audience with a you-are-there verisimilitude. So can the very form that a combat narrative takes. Rod Lurie’s “The Outpost” immerses us in the war in Afghanistan with an existential force rooted in its journalistic authenticity; there isn’t a fake arc in sight. And now, one week later, we have “Greyhound,” which isn’t a factual story — it’s based on the 1955 novel “The Good Shepherd,” by C.S Forester — yet it feels like one, because it’s a naval drama that confines itself to the moment-to-moment logistics of battle. In February 1942, the Greyhound is leading a convoy of 37 troop-and-supply ships through the most dangerous section of the North Atlantic: the so-called “Black Pit,” named for the fact that it’s too far from either continent for the military to maintain air cover. For approximately 50 hours of travel time, the ships are on their own, navigating the darkest of storm-tossed waters — though the real threat are the U-boats that keep popping up like the shark in “Jaws.” Can the crew of the Greyhound blow a hulking submarine out of the water before the sub does the same to them? Krause has a knack for barking out directions at his men with a turn-on-a-dime precision that can serpentine a ship like the Greyhound right out of the path of a speeding torpedo. Though much of the action is set in the open air of the ship’s command perch, “Greyhound” often feels like a submarine thriller: tense, tight, boxed-in. A lot of the battleships-at-sea images are digital, and you can tell, yet even so the film does a scrupulous job of recreating actual war footage. The fetishistic military detail is, in many ways, more potent than the drama, since “Greyhound,” which was scripted by Hanks and produced by his company, Playtone (the director is Aaron Schneider), Most of the characterizations feel a little thin (because, frankly, they are). Yet that doesn’t mean they feel false. Actors like Stephen Graham, as the loyal navigator Cole, and Rob Morgan, as the quietly compassionate African-American messmate George Cleveland, make their presence felt. “Greyhound,” a battle drama that’s only 80 minutes long if you don’t count the credits, turns war itself into the main character. The picture takes us through an experience, with a quota of spectacle but no gratuitous “explosive” razzmatazz, and it’s grounded in Hanks’s finely etched but nearly minimalist performance. Hanks’ Krause, known to his friends as Ernie, is the officer as gung-ho conservative gentleman. When we first see him, he’s saying his prayers and washing his face, and the film then cuts to a Christmas 1941 hotel-lobby rendezvous between Krause and his beloved, Evie (Elisabeth Shue), parting just as the war begins. The scene humanizes an officer who turns out to be a sternly religious man who lives every moment by a strictly observed code. He keeps a rigorous watch on his men (he considers it a breach of ethics if they so much as utter a curse word), he says grace over the most makeshift snack, and when he learns that the radar is down, even in the heat of a U-boat attack he doesn’t bark out a word of frustration. He says “Understood” and thanks the bringer of bad news. When the mortars aren’t firing, the movie ebbs, flows, occasionally sags, and sometimes rivets. At one point a U.S. oil tanker comes out of nowhere, and as the two ships edge close enough that the Greyhound scrapes a gash into the side of the other ship, we realize it’s a Titanic situation, with our heroes as the iceberg. The Germans intercept the radio signal to send mocking messages (“Did you think you’d slipped away from this gray wolf? You and your comrades will die today”). And on the final day, when the Greyhound crew have used up nearly all their depth charges and the air cover comes in seemingly in the nick of time, you feel a surge of relief and triumph. What was it like to fight in WWII? For those of us who’ll never know, that question has a thousand answers. “Greyhound” does a sturdy job of depicting one of them.