[PAR35]

I can see $2 billion for a top of the line sub. But over $3 billion for a destroyer with only 2 6" (155mm) guns? Build 3 more subs for the same cost.

[Strategerist]

But over $3 billion for a destroyer with only 2 6" (155mm) guns?

Those aren't the primary weapons of any destroyer.

And you can't escort and defend surface ships with submarines.

[Bald Eagle777]

1) Double the sub fleet (this will take years).
2) Deploy them to the Pacific Command