@Young:
So is it safe to say that purchasing subs is only viable if you have the upper hand on naval supremacy?
I believe they can also be a valuable purchase toward attaining naval supremacy. If the fleets are somewhat close, a large sub purchase is a good way to swing it in your favor.
As an example using David Skelly’s calculator:
Attacker has 4 CV with 8 fighters, 2 subs, 2 DD, 2 C, 2 BB
Defender has 3 CV with 6 fighters, 2 subs, 2 DD, 1 C, 1 BB
This battle is a 97% win for the attacker. I then ran two scenarios: one where the defender adds a loaded CV, and one where they add 6 subs.
Extra loaded CV: 62% for the attacker
Extra 6 subs: 54% for the attacker
Once you have a solid set of power ships, large sub buys seem to be the way to go