Sorry, I'm late to the party, have been in hospital. What Gepard says is right. If the terrain has a big time span, one in which Red Side has no carriers nor cruisers up to a certain date, then it would work as intended. But the moment you fly a single mission in a year when the Red nation has a carrier available, it's back to a naval battle ala SF2 North Atlantic.
Just an opportunity to consider, my Nations Expansion mod adds Soviet/Russian Naval Aviation as a separate service. The terrain could be limited to the Soviet nation only, while all that is navy related is given the SovietNavy service I added with the mod, by editing each object's userlist.ini file. That way, it's problem solved, it would work just fine and you'd get only Blue Side with carriers.