What had seemed like a large carrier became the largest carrier then built.
What had seemed like a successful submarine attack became the sinking of the largest warship ever destroyed by a submarine.
Enright's six torpedoes gained historical weight months after they had left the tubes.
Few naval victories have expanded so dramatically after the shooting stopped.
Shinano's loss also became a counterpoint to Yamato and Musashi
The three sister hulls met very different ends.
Musashi died under repeated American air attack during the Battle of Leyte Gulf.
Yamato was destroyed by a huge carrier-air assault during Operation Ten-Go in April 1945.
Shinano was sunk by one submarine.
At first glance, this seems to suggest that Shinano was dramatically weaker.
The comparison is misleading.
The ships did not meet their attackers in equivalent conditions.
Musashi and Yamato were completed battleships with experienced crews.
Their systems had been operational for years.
Shinano was a new conversion whose completion remained underway.
The number of weapons required to sink each ship therefore tells as much about readiness and damage containment as it does about raw structural strength.
Shinano's short life prevents us from knowing what she could have become
Had Shinano survived the transit to Kure, completed fitting out, conducted trials, and trained her crew, historians might remember her very differently.
She might have served primarily as an aircraft-support carrier.
She might have been used defensively near Japan.
She might have been destroyed later by American carrier aircraft.
She might have survived the war damaged in port.
There is no way to know.
Her actual history ended before those possibilities became real.
That is part of the fascination.
The ship remains frozen in transition.
Battleship becoming carrier.
Shipyard project becoming commissioned vessel.
Crew becoming organization.
Potential becoming capability.
Archerfish attacked in the middle of every transformation.
The ship never reached the other side.
The question "How could four torpedoes sink her?" therefore has the wrong emphasis
The better question is this:
Why could Shinano not stop four torpedo hits from becoming shipwide flooding?
The answer is much clearer.
Because the carrier was unfinished.
Because watertight integrity had not been properly established.
Because doors and closures were missing or open.
Because bulkhead penetrations had not all been sealed.
Because important pumping capability was incomplete.
Because the crew had little time to train together.
Because civilians still complicated the shipboard organization.
Because the captain initially trusted the ship enough to continue at substantial speed.
Because water kept spreading while every corrective action consumed more of the remaining stability.
Four torpedoes were the initiating damage.
The system behind the hull turned them into a fatal event.
The mystery becomes smaller once the ship is viewed from inside
From outside, Shinano looked nearly impossible to sink.
A flight deck hundreds of feet long.
A Yamato hull.
Thousands of tons of armor.
A displacement approaching 70,000 tons or more depending on loading.
Three destroyers nearby.
Propulsion powerful enough to drive the giant close to 28 knots.
Inside, the picture was different.
A missing closure.
An unfinished cable penetration.
An open hatch.
A pump not yet delivered.
A sailor who did not know the ship.
A civilian who did not understand an order.
A list increasing by another degree.
A compartment that should have remained dry beginning to fill.
The sinking happened inside those details.
Naval survivability is built from details nobody notices until they fail
The strongest ships are not simply those with the thickest armor.
They are those that continue functioning after damage.
That requires redundancy.
Subdivision.
Training.
Discipline.
Communication.
Pumping.
Emergency power.
Repair materials.
Correct command decisions.
Shinano possessed some of these in design.
She did not possess enough of them operationally.
This difference is what turned a powerful hull into a vulnerable ship.