In the winter of 1942, as Nazi forces march across Europe with their sights set on Great Britain, thousands of ships from North America transport men and material across the Atlantic. Passed over for promotion for years, longtime U.S. Navy officer Ernest Krause (Tom Hanks, who also penned the screenplay) finally receives his first command: leading the destroyer Keeling (code-named Greyhound), and three other escort ships to protect a convoy of 37 merchant vessels. Fast-moving German submarines known as U-boats patrol the waters, brutally enforcing a German blockade. Although the convoy receives anti-submarine air cover when within flying range of American and British air force bases, for a terrifying five-day stretch known as the “Black Pit,” Krause and his men are on their own against U-boats determined to sink the destroyer and the ships it is assigned to protect.