Action in the North Atlantic

The American oil tanker Northern Star is torpedoed and sunk by a German U-boat in the North Atlantic. Captain Steve Jarvis and First Officer Joe Rossi evacuate in a lifeboat with other crewmen, which is rammed and sunk by the pursuing U-boat. The survivors are forced to abandon ship and begin a perilous drift at sea.

The lifeboat passengers endure eleven days adrift, facing exposure, dwindling supplies, and constant fear as they struggle to stay alive. They share resources and offer each other hope in a grueling sea ordeal. The crew clings to the possibility of rescue until help finally arrives.

In a brief interlude ashore, Steve spends time with his wife Sarah, offering a glimpse of civilian life interrupted by war. Their reunion provides a personal counterpoint to the ongoing naval crisis. The moment is fleeting as duty soon calls them back to the sea.

Joe Rossi meets singer Pearl O'Neill and marries her, marking a personal milestone amid wartime upheaval. The coupling underscores the human costs and personal stories entwined with the merchant marine's perilous service. Life continues off the deck even as ships face danger at sea.

The Northern Star survivors gather at the maritime union hall, awaiting new assignments as the war effort continues. The mood mixes relief at survival with anxiety over uncertain futures at sea. The gathering signals a transition from rescue to active duty.

The survivors are assigned to a new Liberty ship, the Seawitch, commanded by Captain Jarvis with Rossi as First Officer, signaling a return to duty. The crew steps aboard a fresh vessel and steels themselves for a dangerous convoy run. Duty and camaraderie anchor them despite looming danger.

The Seawitch sails with a convoy bound for the Soviet port of Murmansk, armed with anti-aircraft guns and dual-purpose cannons manned by Navy gunnery personnel. The voyage resumes the perilous bridge between merchant and military wartime operations. The ship carries essential supplies under the eye of patrols.

The convoy comes under attack from a German U-boat wolfpack and must disperse to survive. Seawitch employs evasive maneuvers to avoid torpedoes and keep the ships' cargoes moving. Tension rises as danger closes in from under the sea.

To shake the hunter, the Seawitch goes silent and hides at the edge of the Arctic icepack. The tactic buys time, exploiting the high-risk, high-reward nature of Arctic navigation. The crew remains vigilant as the threat looms nearby.

After the U-boat breaks off, the Seawitch restarts her boilers and sails toward Murmansk. The ship presses on under the threat of pursuit, relying on speed and discipline to reach safety. The crew steels themselves for further combat if needed.

German Luftwaffe planes attack the Seawitch, dropping bombs and firing machine guns. Captain Jarvis is wounded in the bombardment and eight crew members are killed in the assault. First Officer Rossi now faces command under collapsed conditions.

The same U-boat returns and torpedoes Seawitch, but Rossi conducts a clever ruse by creating smoke and fires on deck, ordering an abandon-ship signal to draw the captain in. The tactic buys the crew time and diverts the submarine from finishing the ship. The suspense tightens as the two vessels play a deadly cat-and-mouse game.

Seawitch rams and sinks the U-boat, turning the submarine threat into a ship-focused victory. The crew anticipates reaching Murmansk with the enemy neutralized on that front. The decisive action shifts the balance of danger to a safer passage forward.

Seawitch arrives at Murmansk and is saluted by a squadron of Soviet fighters. A large crowd on the Russian docks enthusiastically welcomes the American crew, including surprise appearances by female longshoremen. The moment marks a rare international bond forged in wartime.

The film closes with an excerpt from President Franklin D. Roosevelt paying tribute to the valor of America's Merchant Mariners and their important contribution to the war effort. The closing voiceover honors the unsung workers who kept supply lines open. The message underscores the broader heroism of the home front at sea.