They learned about damage-control difficulties.
They learned about the spreading flooding.
Only then could the American attack narrative and Japanese loss narrative be combined.
This produced the historical explanation available today.
Without the Japanese evidence, Archerfish's story would end with torpedo explosions.
Without the American evidence, Shinano's story would lack the detailed pursuit and firing solution.
Together they reveal why four hits achieved such an extraordinary result.
Shinano's sinking remains valuable because it defeats simple explanations
It was not simply American technological superiority.
The Japanese ship was technologically impressive.
It was not simply Japanese incompetence.
The strategic decision to move the carrier responded to a real threat from American bombing.
It was not simply luck.
Enright conducted a determined six-hour pursuit and achieved an excellent firing position.
It was not simply design failure.
Many protective features were sophisticated.
It was not simply four torpedoes.
Those torpedoes began a much longer failure process.
The historical truth lies in the interaction.
Skill.
Opportunity.
Strategic pressure.
Incomplete construction.
Command assumptions.
Crew readiness.
Naval architecture.
Damage control.
Time.
Remove one factor and the result might change.
That is why the question has lasted
People look at Shinano's displacement and then look at the number four.
The numbers appear incompatible.
They are not.
Tonnage measures mass.
Torpedo count measures impacts.
Neither measures damage-control capability.
The hidden variable was containment.
Once containment failed, four became enough.
The carrier was strongest where Archerfish did not need to fight it
Archerfish did not have to defeat Shinano's aircraft.
There were no effective carrier air operations to overcome.
The submarine did not have to penetrate the armored flight deck.
It did not have to duel antiaircraft guns.
It did not have to attack the main armor belt with naval artillery.
It approached underwater at night and attacked buoyancy.
Every weapon system has a way around another weapon system.
That is what makes combined naval warfare complex.
Shinano's strongest characteristics were almost irrelevant in the encounter she actually faced.
The final historical irony lies in what Shinano was supposed to provide
The carrier had been redesigned after Midway because Japan needed stronger aviation capability.
She incorporated lessons from carrier losses.
She carried heavy protection intended to preserve aviation operations.
She was supposed to help support other carriers and replace aircraft losses.
She never launched a wartime strike.
Instead, she became a lesson in submarine warfare and damage control.
A ship designed in response to one set of naval disasters became another kind of naval disaster before entering normal service.
In the end, Archerfish did not sink an invulnerable carrier
There was no invulnerable carrier.
There was an enormous unfinished ship whose appearance suggested a degree of readiness she did not possess.
Enright's torpedoes revealed the gap.
At 3:09 a.m., six weapons entered the water.
Four reached Shinano.
The carrier remained upright.
Her engines continued turning.
For a while, the Japanese officers could believe the Yamato-class hull had done what it was built to do.
Then water moved through spaces where it should have stopped.
The list increased.
Men tried to counter-flood.
Pumps could not keep pace.
More spaces disappeared beneath water.
Machinery failed.
The giant slowed.
Then stopped.
Destroyers took tow lines but could not move her effectively.
By 10:18, Captain Abe knew the ship was lost.
At 10:57, Shinano rolled and sank.
The carrier's armored flight deck disappeared last into a sea that had entered hours earlier through the starboard side.
The four torpedoes were enough because they did not need to destroy 72,000 tons of steel.
They only needed to let the Pacific Ocean inside faster than Shinano could keep it out.
And on her first real voyage, before her crew had learned the ship and before the shipyard had finished sealing her, that was exactly what they did.