During the Pacific War, both USN and IJN operated (or at least preferred to) carrier battle groups composed of multiple carriers plus their screening ships. IJN's Kidō Butai - which carried out the assault on Pearl Harbor - consisted of 6 carriers. Late in the war, USN mainly operated Fast Carrier Task Forces, which were composed of multiple task forces of 3-4 carriers each plus their escorts.
During the inter-war period when people weren't familiar with how to use carriers, the USN operated single-carrier groups. Fleet Problem XIII exposed weaknesses with this setup, and recommended more carriers per group:
The exercise showed that one carrier was insufficient for either fleet attack or area defense, so the practice of two or more carriers operating together became policy. Admiral Harry E. Yarnell said that six to eight carriers would be required for a Pacific campaign, but no orders were placed for new carriers, as Depression-era financial difficulties caused President Herbert Hoover to limit naval expenses.
My question is: why did WWII-era carrier battle groups require multiple carriers? And why did the USN go back to single-carrier groups? Was it:
- Putting enough planes in the sky
- Eliminating a single point of failure, the carrier