Germany's U-boat campaign aimed to starve Britain out of the war, sinking merchant convoys faster than they could be replaced. This film follows the Royal Navy's response, built around Vera Matthews, who leads the reformed WRENS, and a retired war gamer brought in to model U-boat tactics on paper before the Navy tries to beat them at sea. The WRENS assigned to the newly formed war gaming room become central to the story, running scenarios that let commanders test convoy formations and escort tactics against simulated wolf packs without losing a single real ship in the process. Archival footage of convoys, U-boat crews, and the operations rooms where these war games actually took place anchors the narrative, alongside expert commentary tracing how battle of the Atlantic tactics evolved from guesswork into something closer to applied mathematics. The film treats the war gaming room as a hinge point in the Atlantic campaign, where a small group of women effectively rewrote how the Navy fought U-boats.