Destination Tokyo

The Copperfin leaves Mare Island Naval Shipyard on a secret mission. Captain Cassidy opens his sealed orders, directing the vessel first to the Aleutian Islands to rendezvous with a PBY Catalina and take aboard meteorologist Lt. Raymond. The squad also learns they must reach Tokyo Bay to gather weather intelligence for the upcoming Doolittle Raid.

At the Aleutian rendezvous, Copperfin meets a PBY Catalina and takes Lt. Raymond aboard. The crew follows the new orders toward Tokyo Bay, carrying the meteorologist who will provide crucial weather data. Tension in the crew rises as they prepare for what lies ahead.

Copperfin alters course toward Tokyo Bay to obtain vital weather intelligence for the Doolittle Raid. The mission depends on accurate atmospheric readings and careful navigation through the Pacific. Lt. Raymond begins processing data that could affect bombing schedules.

Two Japanese floatplanes attack Copperfin as it approaches its destination. Both planes are shot down, but one pilot parachutes into the water. Mike, a crewman, descends the hull to assist the downed pilot and is stabbed to death in the process.

New recruit Tommy Adams fires at the parachuted Japanese pilot, his hesitation contributing to Mike's death. He cannot shake the memory, and volunteers for a dangerous task later to atone for his mistake.

To expiate his error, Tommy volunteers to defuse an unexploded bomb lodged under the deck. Cassidy directs the improvised operation, which requires calm, courage, and steady hands under pressure.

Mike is buried at sea as the crew mourns his loss. Tin Can reveals that every Allied death causes him great pain, initially angering the others until they understand his deeper empathy.

Raymond, who lived in Japan, discusses how the Japanese military faction led the nation into war. His perspective adds nuance to the crew's understanding of the conflict and its moral complexities.

As Copperfin nears Tokyo Bay, the crew must negotiate defensive minefields and anti-torpedo nets. They seize a chance to maneuver by following a Japanese ship into the bay, keeping their presence hidden.

That night, a three-man party including 'Wolf' goes ashore to take weather observations. The mission emphasizes secrecy as they gather essential environmental data.

Tommy is diagnosed with appendicitis, and pharmacist's mate 'Pills' must operate using improvised tools with limited ether. The surgery succeeds, and Cookie the cook begins baking the pumpkin pie he promised Tommy.

Raymond broadcasts the collected weather information in Japanese to avoid detection, but Japanese forces search the bay anyway. The crew remains alert as they monitor for countermeasures.

The submarine stays hidden and peeks through the periscope as the Doolittle Raid unfolds. The crew experiences a rare, hopeful glimpse of the air operation from their submerged vantage.

Copperfin recovers Raymond and his team and slips out of the bay as anti-submarine nets are opened to let it pass, following an exiting Japanese ship. The escape is tense but successful.

In a desperate final action, Copperfin sinks a Japanese aircraft carrier and endures heavy escort counterattacks. After long hours of depth charges, Cassidy drives a destroyer to the bottom and leads the crew home safely.