How many of these hunks of metal do I need to have to take on Japan's fleet? It takes about nine months to build one. Playing as Netherlands in Batavia.
And to answer my own question: Three is not enough, but four to six might be.
A story of four fleets. Two minor ones, two major ones. Locale: Sea area North of New Guinea.
Course of events:
1. Have a fleet of three heavy cruisers (shown above) and 20-ish destroyers as screen act as the strike force. Let the Caustic guy command. (He was the best I had. Plus he had Cruiser Captain.)
2. Set up 400 heavy fighters to patrol the skies to nullify any air superiority the enemy might get from the carriers.
3. Have a single destroyer patrolling the seas doing reconnaissance work. (For some reason, my strike force would not budge unless I had full knowledge of the opposing fleet. Even though they were fully visible in combat!)
4. Set up a new fleet of my oldest submarines, with a greenhorn level 1 admiral, to convoy raid the area. I had to lure the Japanese out somehow, right? The reason behind the admiral choice was to have my strike fleet's admiral take command when he arrived, due to his higher level.
5. Their escort fleet arrives to protect the convoys. My submarines wisely start running away.
6. My strike force starts out of New Guinea, heading to destroy the escort fleet. Luckily just slowly enough to not quite finish with the combat before the next step.
7. Their carrier strike force arrives. It was 40-50 ships in size. To my surprise, most of its destroyer screen had been replaced with light cruisers, which stacked the odds heavily against me. Light cruisers are incredibly resilient as screens. To make matters worse, one of my three heavy cruisers (my pride of the fleet) had somehow been heavily damaged in the fight with the escort fleet and was already running away, with no way to override it.
I had previously tested (when I had their strike force in sight) that I had to set my strike fleet to "always engage" for them to not run away screaming, and as soon as I could see their forces entering combat, that's what I did.
My ships could not hold their own for too long, and had to run away but it was a victory nevertheless. Half of my screens are now at the bottom of the ocean, and most ended up there when they were trying to run away.
I sunk two of their heavy cruisers, many light cruisers and many destroyers. Not enough to lower their screening efficiency below 95 % at any point, however. I sunk numerically more than they sunk mine, and also much more expensive ships than mine. It was a good trade.
My heavy cruisers all survived, but need to spend a few months at a dockyard, and I'll be building two more, as well as replacing my sunk screens.
As far as I can tell, the United States has not had a single clash with the Japanese fleets thus far. So this has all been a solo effort from the Netherlands.
Also worthy of note, for some reason, the Japanese stopped trying to invade my territory navally a long time ago. I wouldn't have needed the elaborate set-up had they still been running invasion support missions with their navy. The AI works in mysterious ways.