USS Archer-Fish Sinks the IJN Shinano
Not only was the Shinano dangerously incomplete in regards to ability to sustain and recover from battle damage, she had the misfortune to come across a US submarine, the Archer-Fish, only hours after departing Yokosuka. The submarine picked her task group up on radar and approached - probably believing Shinano to be a large merchant ship or group of smaller merchant ships considering her escort and the fact that her existence was unknown to US Naval authorities.
After a four hour cat and mouse approach - made easier by the fact that not all of IJN Shinano's boilers were online and her top speed was reduced - Archer-Fish fired six torpedoes at the aircraft carrier and dove deep. Of the six, four struck the carrier and immediately caused serious flooding along her starboard side.
Ironically, the damage was not immediately lethal. Shinano's crew bravely fought the flooding brought on by the four torpedo hits for four hours before she was no longer able to sustain forward progress, and even then the ship remained afloat for more than two additional hours. Her crew tried to pump out the seawater, they even tried to counterflood to correct a rapidly developing list to starboard that threatened to capsize her.
But in vain. Shinano's pumps didn't work correctly, her lack of watertight compartmentation hindered efforts to counter flooding, and her crew - albeit brave - did not have sufficient experience in damage control procedures. Finally, she capsized and sank taking almost 1500 men with her - including her captain. The IJN Shinano remains a little over 100 miles off the Japanese coast.