Crossing the pacific either way, and the island battles makes carriers a much needed addition. They played a huge role in the era and on this 100 map it has to have them in some form. Penalize the crap out of them in the beginning to get a feel for balance. I know you want them in the game, just begin and the players will find and take advantage of things which will be reported and can be handled quickly. Before it really wasn't as important as it is now.