That was close for a torpedo attack against such a large target.
Enright had six bow torpedo tubes available.
He intended to use all of them.
The torpedoes were set to run shallow.
U.S. Navy historical analysis says Enright deliberately wanted the weapons to strike just below the waterline, above much of the deepest torpedo-bulge protection, increasing the likelihood that the damage would promote flooding and list.
At 3:09 a.m., Archerfish fired six torpedoes.
The weapons crossed the short distance.
Four hit Shinano's starboard side.
The submarine remained at periscope depth long enough for Enright to observe at least the first impacts.
Then he ordered Archerfish deep.
Destroyers were already reacting.
Enright had no reason to remain near the surface and watch.
The attack had been made.
His immediate problem was surviving the escorts.
Behind him, the largest aircraft carrier then afloat had been hit four times.
Four torpedoes sounded serious, but not necessarily fatal
Four submarine torpedo hits could destroy many warships.
Shinano was not an ordinary warship.
Her ancestry mattered.
Yamato-class ships had been built around enormous armored volumes and extensive underwater protection.
Captain Abe apparently believed the carrier could absorb the damage.
The ship did not break apart.
There was no immediate catastrophic magazine explosion.
The propulsion system continued operating.
Shinano remained capable of movement.
From the bridge, this could make the initial situation appear less desperate than it actually was.
The carrier developed a starboard list, but counter-flooding could theoretically correct it.
Damage-control teams went below.
The ship continued toward Kure.
The torpedoes had not killed Shinano instantly.
They had opened the door for the sea.
What happened next depended on whether Shinano's internal subdivision could close that door.
It could not.
The location of the hits mattered
The torpedoes hit along the starboard side in positions that damaged the carrier's underwater protection and flooded important spaces.
U.S. Navy historical analysis notes that the hits occurred in a vulnerable region below the waterline but above the deepest anti-torpedo bulges.
A torpedo-defense system generally works by accepting controlled destruction.
The outer portion of the ship absorbs or dissipates explosive energy.
Voids and liquid-filled compartments reduce the force transmitted inward.
Internal bulkheads are then expected to remain intact enough to keep seawater out of vital spaces.
This does not mean the hull remains dry.
It means flooding should remain confined.
That last word is critical.
Confined.
Warship survivability depends heavily on subdivision.
A ship can lose several compartments and remain afloat if the water stays inside them.
The remaining sealed volumes preserve buoyancy.
The ship lists, but counter-flooding or pumping can restore stability.
Machinery survives because water is prevented from reaching it.
Shinano's incomplete internal condition undermined this entire principle.
The torpedoes flooded the compartments they physically damaged.
Then water found paths beyond them.
A watertight bulkhead is useful only when it is watertight
The concept sounds painfully obvious.
A steel bulkhead can divide one compartment from another.
If there is an open door in that bulkhead, water can pass through.
If a cable hole has been cut and not sealed, water can pass through.
If a pipe penetration remains unfinished, water can pass through.
If a hatch remains open, water can pass through.
In ordinary operation, many of these openings are convenient or necessary.
In battle, they determine whether local flooding remains local.
Postwar analysis of Shinano repeatedly returned to this problem.
Because construction had been rushed, the carrier's overall watertight integrity had never been properly completed or tested.
Some watertight doors had not yet been installed.
Numerous penetrations made for pipes and electrical cables remained inadequately sealed.
Hatches were open because workers still needed access.
The ship was physically incapable of compartmentalizing flooding as effectively as the design intended.
This explains the central paradox.
Shinano possessed immense armor, but water does not need to penetrate armor if it can move through an opening already left inside the ship.
The torpedo creates the initial breach.
The unfinished construction creates the secondary breaches.
The second process can destroy the ship long after the explosion ends.
Shinano had never properly demonstrated her watertight integrity
A completed warship undergoes trials.
Systems are operated.
Valves are tested.
Doors are checked.
Pumps are run.
Compartments are inspected.
Crew members learn where equipment is located.
Damage-control teams practice responding to flooding and fire.