I have just played as Japan, specifically so I could learn all about how to get good on a Naval basis. (Always let myself down in the past with my Navy). Japan and Italy have similar IC's to begin with but Japan does have better doctrines. Here's what I did.
I researched DD and CL's to a minimum level 4 before building any, most were at level 5 though. Kure Naval Yard research very quickly. I also went years ahead of time researching all possible naval doctrines. (All done by 1942) I also researched aircraft carriers to a level 5, but in the meantime used my IC to build 2 x 3 Carriers plus 6CAG's. (I did use a lot of IC to build and research Naval Bombers in a big way - eventually having 38 Naval Bomber units - researched to Advanced Level by 1942). I also used remaining IC for upgrades, and about 60 infantry units all with brigade attachments of varying types.
I conquered Communist & Nationalist China, Xibel San Mai, Xanshi, Dutch East Indies, Papua New Guinea, India, Pakistan, Indochina, all of the Pacific Islands. At this stage USA declared war. So whilst being patient enough for my Navy to finish building (I added another 4 carriers at level 5) and keeping them in Port they eventually finished and I was ready.
Its 1st Aug 1942. USA has 338 vessels, including 25 Carriers and 38 BB's. By April 1943 USA has 38 serviceable ships all either DD, CL or TP's.
I organised by Navy into 4 battle groups each comprising 4-5 Carriers, 8 CL's, 8DD's and remainder 3TP's per group. You don't need 'soaks' as some gamers call them, they are a waste of IC and time. This added improved landing and expansion into the American half of the Pacific. I concentrated on taking Pearl Harbour and surrounding Islands. I suurounded/blockaded the islands with my 4 battel groups and then let USA's navy come for me. With 38 naval bombers operating from Paerl Harbour and Hawaii it was like a turkey shoot. My ships Org. levels were 66 against the USA's of 41 !!! My carriers org levels were between 103 and 113 depending on the level of carrier.
Its fair to say that my Naval bombers did a lot of damage, however my Carriers kicked butt with more than up-to-date CAG's and also air doctrines and Radar tech's now being sorted I kicked ass beyond all expectations. In one cheeky little move I built 3 level 5 CA's and used these to escort 5 TP's to Colon. This cut off any chance of USA's Atlantic fleet (what little of it was left) from coing through the Panama Canal and kicking butt.
The balance of my Navy ie. existing BB's BC's CA's were used to destroy the British and shut down their use of the Suez canal by effectively blockading it.
I have just landed on USA's western seaboard and found that USA have this amazing ability to ghost in 27 divisions to surround my gains and stop me moving further inland. This is where my CAS and TAC planes will kick ass, but will I build them in time before the Yanks push my men into the sea ???
USA has an army of 287 against my 128. I am only going to use 32 divisions to take USA, but will need about 60 CAS planes and 16 TAC bombers to do it. Now I no longer need my Navy I will scale it down to about 50 ships to save fuel and supplies, and get rid of all but 12 naval bomber units too. I am leaving Soviet Union to Germany. They're about 2/3rds there so dont want to steal their thunder.
