Can planes scramble on Japan against lets say… American subs as long as they have subs or destroyers themselves?
I believe that per the wording of the rules, aircraft can scramble in response to ANY combat move that ends in the adjacent seazone. So they can scramble against subs. But they cannot hit them. So there’s no reason to scramble.
Also, if japan has subs, they wouldn’t help Japanese aircraft hit american subs. Only a friendly (in this example a Japanese, German, or Italian) destroyer would allow the defending scrambled planes hit attacking subs (as friendly destroyers assist in combat - this is obviously not the case on attack).