Can someone explain this

[BomberEscort]

Can someone explain why I can't build attack submarines? Here is a save...

 

[KMadCandy]

i'm too lazy to load the save, but i have a guess. all other late game ships require oil OR uranium. attack subs require uranium, oil can't substitute. so you probably have oil but not uranium?

 

[Sephlock]

Or you have Uranium, but not Fission, which is required to actually USE Uranium.

 

[KMadCandy]

oops yeah i didn't specify, that's part of what i mean by "have uranium" = hooked up in your cities.