I don't get the US Sub in sz50.
The US sub won't fight if Japan don't bring it's lone DD to sink it,
2 fighters vs 1 BB is a tough fight without the DD to soak the hit.
You got to make a choice, bringing that CA along won't do anything extra to be able to hit that sub. The choice is where do you send your single DD? To kill that sub or to pearl harbor? Do you kill USA sub and commit 3rd carrier also to Pearl Harbor, which case UK ships survive?
Not killing the sub means Borneo / Sumatra transports are in deep trouble. Having a lone AC in sz37 is not good either if Japan went after Indian UK ships. That sub will cause head aches for sure.