The torpedoes began the sinking.
The unfinished ship completed it.
Captain Abe stayed aboard
The abandon-ship order came only when the carrier's fate was essentially irreversible.
By then, Shinano had developed a severe list and the remaining personnel were trying to escape from a massive hull approaching capsize.
Captain Abe did not survive.
U.S. Navy historical summaries state that he chose to go down with the carrier.
The loss of life was substantial.
Current U.S. Navy historical figures give approximately 1,435 men lost, with around 1,080 rescued, including civilian workers and a small number of personnel associated with the Ohka units aboard.
The exact composition of those aboard complicates simple statements about "crew casualties."
Shinano carried sailors, officers, aviation-related personnel, and civilian shipyard workers.
Some men had been aboard because the ship remained unfinished.
That fact connects even the casualty total to the rushed departure.
Workers who normally would have completed their jobs inside a shipyard instead went to sea with the ship.
The unfinished construction and the human presence required to finish it had become inseparable.
Archerfish did not know what she had sunk
Enright and his crew knew they had attacked a very large carrier.
They did not understand exactly what Shinano was.
American intelligence had seen photographs of the ship, but knowledge had not been distributed in a way that allowed Archerfish to identify her confidently during the patrol.
Initial American assessments underestimated the target.
Enright produced sketches and argued that the ship had been much larger than ordinary identification suggested.
Only after Japan's surrender did the full truth emerge.
Archerfish had sunk Shinano, the converted third Yamato-class hull and the largest aircraft carrier yet completed.
U.S. Navy history describes her as the largest warship ever sunk by a submarine.
Enright received the Navy Cross.
Archerfish received a Presidential Unit Citation.
The submarine that had begun the evening on a lifeguard mission had destroyed one of the most remarkable ships Japan ever constructed.
The magnitude of the result was almost accidental.
Enright knew how to solve the tactical problem.
He did not need to know the weaknesses inside Shinano.
He simply had to put torpedoes into the correct part of the hull.
The torpedoes did not have to defeat every layer of Shinano's armor
A common misconception treats armored warships as though every incoming weapon must penetrate the thickest armor on the ship.
That is not how naval protection works.
The heaviest armor protects particular areas against particular threats.
Battleship belt armor is designed primarily to resist gunfire.
Deck armor addresses plunging shells and bombs.
Torpedo-defense systems use entirely different arrangements below the waterline.
No ship can carry maximum armor everywhere.
The weight would become impossible.
Shinano inherited much of the Yamato hull's protection, but conversion to a carrier also changed aspects of the armor distribution.
The torpedoes did not have to penetrate an 18-inch armored turret face or a thick main belt designed for battleship gunfire.
They struck underwater or near-waterline areas where survivability depended on the layered torpedo-defense system and internal subdivision.
Once flooding crossed those internal boundaries, the extraordinary armor above became almost irrelevant.
Three inches of hardened steel on a flight deck does nothing to stop seawater already inside the lower decks.
This is the central engineering lesson.
Protection must match the threat.
Shinano was heavily protected against certain forms of attack.
She was operationally vulnerable to progressive flooding because the internal completion state undermined the very system intended to contain underwater damage.
Her Yamato ancestry may actually have encouraged dangerous confidence
Yamato and Musashi had reputations as enormously durable ships.
Musashi had survived repeated air attack before finally sinking in the Sibuyan Sea in October 1944.
Yamato would later absorb a massive American carrier-aircraft attack off Okinawa before going down in April 1945.
These ships were not invulnerable, but they required enormous destructive effort under completed combat conditions.
Shinano shared their scale and much of their underwater structure.
That visual and structural relationship may have contributed to the assumption that four torpedoes could not be fatal.
The assumption ignored one critical difference.
Yamato and Musashi were mature warships.
Their crews had lived aboard them.
Damage-control organizations existed.
Watertight systems had been completed.
Personnel understood the ships.
Shinano had barely been commissioned.
A hull can inherit armor.
It cannot inherit crew experience.
A design can inherit subdivision plans.
It cannot inherit watertight integrity when the doors and seals have not yet been finished.
The ship looked like a Yamato-class giant from the outside.
Internally, she was still becoming one.
Comparing Shinano with other damaged carriers reveals the importance of damage control
Many aircraft carriers survived serious battle damage during World War II.
Some absorbed bombs, torpedoes, fires, and near misses that caused hundreds of casualties without sinking.
Others were lost after apparently modest damage triggered secondary fires or uncontrolled flooding.
The difference was not always ship size.
Damage-control quality frequently determined the outcome.
A trained crew could isolate fuel systems, close ventilation, flood magazines, restore electrical circuits, operate pumps, shore damaged bulkheads, and prevent fire or water from crossing boundaries.
A poorly prepared crew could allow relatively localized damage to spread.
The United States Navy learned this lesson brutally during the war.
Damage-control doctrine became an enormous emphasis aboard American ships.
Every sailor could be expected to participate.
Repairs were practiced.