From: Somewhere in the South Pacific.
I think the reason Jeff, is the difference in tactical organization between the IJN and USN carrier air units. The basic USN unit was the Squadron of between 18 and 36 aircraft, whereas the basic IJN unit was the Daitai of 9 aircraft. So basically then the USN early war carrier groups consisted of 4 Squadrons, of VF, VS, VB, and VT.
But now with the IJN Carrier group it starts getting confusing, so here goes; The larger carriers embarked two Daitai in their 'fighter squadron' e.g 18 aircraft, but the Hiryu and Soryu had one and a half units (early in the war). Same with their dive-bomber and torpedo-bomber 'squadrons', but in the big carriers they carried three Daitai each e.g 27 aircraft. But again the Hiryu and Soryu carried less, with two Daitai e.g 18 aircraft.
When you see the Southern Cross, For the first time
You understand now, Why you came this way