The Supercarrier That Never Fought: How the Shinano Became the Largest Warship Ever Sunk by a Submarine

She was built to be the salvation of a dying empire—a steel giant meant to rise from the ashes of Midway and restore Japan’s shattered naval dominance. The Shinano, a 71,000-ton colossus derived from the same hull design as the legendary Yamato battleships, was the largest aircraft carrier ever constructed during the Second World War.

Yet ten days after she was commissioned, she was gone.

Sunk in darkness by a single American submarine.
Lost not in battle fleet combat, but in a covert duel at sea.
A ship so secret that most of Japan’s own navy had never laid eyes on her.

How did a vessel of such scale vanish so quickly?

The answer lies in haste, fear, unfinished steel, and a hunter who had something to prove.

Japan’s Final Gamble: Building the Shinano

By late 1944, the Pacific War had turned decisively against Japan. The humiliating losses at Midway two years earlier—where four frontline carriers were destroyed—had robbed the empire of the striking power that once dominated the ocean.

Japan needed something extraordinary.
Something immense.
Something that could convince the nation that victory was still possible.

The Shinano was that symbol.

Originally laid down as a third Yamato-class super battleship, her incomplete hull was hastily converted into the world’s largest aircraft carrier. Engineers carved out vast hangar bays and reinforced decks, transforming the behemoth into a floating airbase capable of supporting more than 160 aircraft.

Her specifications were staggering:

Length: Nearly three football fields

Displacement: 71,000+ tons

Speed: 27 knots

Range: 10,000 nautical miles

Complement: Over 2,500 personnel

Below the waterline, she carried anti-torpedo bulges meant to absorb underwater impacts. But in the scramble to finish the ship, her massive 16-inch planned armor belt was never installed; in its place was armor less than half as thick.

To the Japanese command, she represented hope.
To naval engineers, she represented compromise.
To history, she represents a paradox.

Commissioning Under a Shadow

On November 19, 1944, the Shinano was officially commissioned at the Yokosuka Naval Shipyard. Ceremonial flags fluttered, brass bands played, and dignitaries saluted the towering supercarrier.

But the celebration barely ended when a lone American B-29 reconnaissance aircraft appeared overhead. Its crew photographed the new warship—the only publicly known image taken before she sank.

The sighting stunned Japanese leaders. Fearing a massive air raid, they issued an urgent order:

Get Shinano to Kure immediately.
Ready or not.

Captain Toshio Abe, a quiet but capable officer, was chosen to take command. He immediately protested:

Watertight doors were missing

Bulkhead cable openings were unsealed

Fire mains and bilge pumping systems were incomplete

Four of twelve boilers were offline

His warnings were dismissed.
Japan needed its supercarrier at sea.

The Hunter: USS Archerfish

While Shinano prepared to leave port, an American submarine glided silently through waters to the south.

USS Archerfish, commanded by Captain Joseph F. Enright, was on his first war patrol with the vessel. He carried the weight of past failure—having once lost the opportunity to attack a major Japanese carrier. Determined not to repeat that mistake, Enright was hungry for redemption.

His crew was seasoned, his boat in good order, and fate was quietly aligning their path toward one another.

A Night Departure into Danger

At 5 p.m. on November 28, Shinano slipped into open water escorted by three experienced destroyers—Isokaze, Yukikaze, and Hamakaze.

Onboard were:

2,000 naval officers and crew

300 shipyard workers still racing to finish her

40 civilian contractors welding, wiring, and sealing compartments as she sailed

Her hangar bays carried a grim arsenal:
six Shinyo suicide boats and fifty rocket-powered Ohka aircraft—kamikaze weapons intended for desperate actions.

Captain Abe wanted to sail by day to train his inexperienced crew, but the general staff refused. No air cover could be provided. Shinano would leave under cover of darkness.

The carrier began zigzagging through the sea, a standard tactic to confuse submarines. It was too little—and too late.

Radar Contact: The Giant Revealed

Archerfish surfaced shortly after dusk. The moon hung full over the Pacific, illuminating a vast stretch of water.

At 8:50 p.m., the submarine’s radar operator detected a massive signature at long range. Enright climbed to the bridge, scanned the horizon, and saw the silhouette of a leviathan.

At first he suspected an oil tanker.
Then he realized the truth.

This was an aircraft carrier.
A huge one.

Despite risk of detection, he ordered continuous radar pings to keep contact. It was a dangerous breach of submarine stealth—but Archerfish was now shadowing a prize far too important to lose.

Shinano Detects the Pursuit

Aboard Shinano, radar operators immediately picked up the American signals. Captain Abe noted the track but showed little concern. One submarine could not sink a ship of this size, he believed. Only a coordinated wolfpack posed a real threat.

Yet what he interpreted as a minor harassment was something far greater—a fatal intersection of flawed assumptions and exhausted machinery.

When the destroyer Isokaze moved to engage, Abe overruled the attack. He suspected a decoy meant to draw escorts away.

His decision, meant to protect the carrier, ensured she would face her hunter alone.

A Twist of Fate: Engine Trouble

Shortly after 11 p.m., an unexpected event changed everything.

One of Shinano’s propeller shafts overheated. She was forced to reduce speed to 18 knots—barely faster than Archerfish at flank speed.

Then, believing the threat had passed, Captain Abe altered course.

He turned west.

Directly toward Archerfish.

Enright, who had temporarily lost contact, suddenly saw his quarry return to his predicted track. The chase was on again.

Setting Up the Kill

Navigating beneath the waves, Enright positioned Archerfish across Shinano’s projected path. At 3:05 a.m., he ordered the submarine to periscope depth. He set his torpedoes to an unusually shallow running depth—only ten feet.

His reasoning was tactical genius:

A shallow hit would strike below the flight deck—precisely where the ship’s weakened armor left her vulnerable.

Moments later, Shinano made a fatal maneuver. Attempting to evade the expected attack, Abe turned the carrier south, unwittingly presenting her broadside to the submarine.

A perfect target.

“Fire One!” — The Torpedo Attack

At 3:17 a.m., Enright committed.

Fire one!
Fire two!
Fire three!
Fire four!

Four torpedoes left the tubes eight seconds apart, followed shortly by two more.

The destroyers above raced past Archerfish, but one crucial detail saved the submarine: their sonar equipment was damaged from prior engagements.

Enright watched through the periscope until the last possible moment.

Two brilliant flashes lit the Shinano’s starboard hull.
Then two more.

Six torpedoes had been fired.
Four made contact.
Each found its mark.

Archerfish dove deep as the counterattack began.

Catastrophe Below Deck

Shinano shuddered with explosive force. Captain Abe felt the deck tilt beneath him. Damage reports came in rapidly—and all were devastating.

The torpedoes had detonated exactly where the armor was weakest:

One ruptured an empty fuel tank and refrigeration plant

Another flooded an engine room

A third destroyed a fire control station

The fourth struck an air compressor room, crippling damage-control

Flooding spread uncontrollably through compartments that had never been properly sealed.

Within minutes, Shinano listed 13 degrees.

Not survivable for long.

The Desperate Fight to Stay Alive

For hours, the crew battled rising seawater. But their efforts were hampered by:

incomplete watertight systems

untrained civilian workers

loss of power

failing pumps and boilers

Captain Abe pushed the engines to full speed—not to outrun the submarine, but to outrun the ocean. The faster the ship moved, the longer she might stay afloat.

But speed also forced more water through her wounds.

By dawn, the list exceeded 20 degrees. The destroyers tried to tow her, but the massive carrier snapped tow cables like thread.

At 8 a.m., Abe ordered flooding of the port boiler rooms to counterbalance the list. For a moment it worked.

Then it didn’t.

By 8:30 a.m., critical pump rooms failed.
By 10 a.m., water reached the base of the island tower.
Shinano was dying.

“Save Yourselves.”

Captain Abe could not bring himself to give the traditional order, abandon ship. Instead he told his crew:

“You are all released from duty. Save yourselves.”

At 10:55 a.m., the Shinano rolled onto her starboard side and slipped beneath the Pacific.

Air pockets burst violently from the structure. Hundreds were pulled under.

Of the 2,515 aboard, nearly 1,455 died.

Shinano had sailed for only ten days.

Aftermath: A Secret Loss and a Record Set

When Archerfish returned to Guam, Enright’s claim was initially dismissed. Intelligence officers doubted a carrier had even been present.

Then Enright produced his sketch—the rounded bow, the unfamiliar silhouette.

Intercepted Japanese signals soon confirmed it:

Shinano was gone.
Archerfish had sunk the largest warship in history ever destroyed by a submarine.

Enright was awarded the Navy Cross.

The Legacy of a Giant Built Too Quickly

Shinano’s loss was far more than a wartime setback—it was a symbol of Japan’s deteriorating naval power. The rushed construction, untested systems, incomplete watertight integrity, and pressure to get her to sea all contributed to her fate.

She embodied a lesson written in steel:

Even the mightiest ship is vulnerable if built on haste and compromise.

Final Reflection

Shinano never launched a plane.
Never fired her guns.
Never saw the battle she was created for.

Her story lives not in triumph, but in caution.
A reminder that engineering shortcuts, bureaucratic pressure, and wartime desperation can doom even the largest of giants.

And in the silent darkness of the Pacific, one determined submarine proved that no warship—no matter how vast—is unsinkable.