Assuming a declared war on America but given hindsight I'd change a lot of things in the prewar production cycle if I were the Emperor. (Not that it'd make much of a difference) Cancel the
Yamato BBs for starters. For roughly the same tonnage 3
Unryu class carriers could be built per
Yamato.
Put more emphasis on pilot training and rotating veteran pilots home to train rookies. Japan had an insane policy of keeping veteran pilots at the front until they were dead or wounded. And they didn't train enough of them. The carrier pilots who fought in the Marianas battle in 1944 were almost all green. By Leyte Gulf they were switching to kamikazes.
Change ASW doctrine radically. Beg, borrow and steal any radar and sonar technology you can from allies and enemies alike. Beat and whip it into the destroyer and escort captains heads that defending merchant ship from subs is their most honorable profession. Cancel wasteful and counter-productive projects like the midget subs and the massive I-400 class in favor of building escorts. Frankly I'd cancel all Japanese sub production except for the advanced ST types. The RO-class in particular was virtually useless.
Scrap all the pre-war battleships for their steel with exception of the
Kongo class. The old and slow
Nagato,
Ise and
Fuso classes contributed very little to the war effort. Build even more escorts with the steel. Use the guns for coastal defence.
Well...there's a million things Japan could have done ahead of time. But assuming war with America they probably would have only delayed defeat given the disparity between the two opponents. Here's a link to a page on combined fleet site that compares Japan and the USA economically. Quite an eye-popper considering the historical decisions made.
http://www.combinedfleet.com/economic.htm
