Taiho..
Shinano?
How embarassing. Some expert I am...thanks for bringing me back to earth.
Yes, the Shinano was the one I was thinking of.
The Taiho was the biggest carrier in the Japanese fleet (some 33,000 tons) at the time and was their flagship, until the Shinano was launched, and the Taiho was second only in size to the USS Saratoga (which I believe was still bigger than the Essex class types).
Yeah, I got them mixed up. The Shinano, built on a Yamoto hull was (at around 59,000 tons), was hit by four torpedoes and turned into a giant fuel air bomb. Her maiden voyage lasted only 17 hours before she sank. What a waste for them. She had a flight deck armored with 30cm of steel, overlaying concrete. She was sunk by her captains stupidity and poor training of the crew. Bad for them. Good for us.
The Taiho, however did fall prey to a single torpedo, and she was torpedoed by the Albacore, not the Cavalla.
Sigh. I just stuck those two incidents in a mental blender...:(