It would have to be much earlier than the Two Ocean Navy Act.
If the Japanese are commencing the conversions in 1938, and the U.S. gets wind of it, then the 1938 Vinson Act (passed in May) is much closer to the mark. Adding another
Yorktown when they're already putting
Hornet into the pipeline makes perfect sense.
Essex design work wasn't far advanced enough yet, and they're in a hurry by this point (which is why
Hornet got ordered in the first place).
That would probably make it available by end of spring 1942, when it would be a godsend to Nimitz. Of course, it's likely to have a lot of the same teething issues as
Hornet did, but hey, you take what you can get.
I do not know if the IJNAS flight schools or the Japanese aviation industry could supply the 400 additional fliers or 200 aircraft?
Normally I would (of course) agree, Mac. But if the IJN is putting this in train by 1938, I think it is reasonable to think that they have the time to adjust their training programs to produce the pilots in time. That is...a good four years or so to work with. Especially if they want to raid the light carriers for the best pilots.
Aircraft production is an interesting question, however. Hmmmm....
- The Japanese produced about 500 A6M Zeros by the end of 1941, and I have my doubts they can increase that by much without cutting into other aircraft production. It is enough to fill out 8 fleet carrier fighter complements if you prioritize those squadrons over absolutely everything else.
- The Japanese produced 661 B5N Kates by late 1941. Again, probably enough with top priority -- they only need 40-50 or so to do two more carrier complements.
- The D3A1's might be a push. They only started production at the end of 1939, and not much above 300 had been produced by end of summer 1941. While it might be possible to get enough set aside for two new carriers, I am less sure there will be enough stick time for training by the war begins. Otherwise, they make do with D1A's, oor raid the light carrier squadrons, or just short themselves in the interim, unless they are willing to seriously rework military aircraft production priorities.
Obviously the pilots need stick time in these new aircraft, and that's why this gets tricky. Simply having an airplane rolling out the factory door is not enough. The pilots need time learning these new machines. So you have to factor that into the schedules.
I think it's at the margins of doability, with the lead time we are talking about, but this reinforces my suspicion that the two new carriers don't go to Pearl Harbor, but get sent south instead, where the risk is lower. They would probably do some training with the Kido Butai carrier divisions in mid-late 1941, though.
It is possible that pilot quality could suffer for the light carrier squadrons, unless the IJN can somehow really do some major flexing in war economy planning early enough.