aircraft carriers seem to be somewhat useful. as FW190F said, they are good at defense. if u look at the math, you gain 3-3-4 at 38 IPC when playing basic AA. Also, carriers make decent assault platforms for attacking aircraft. if youre really into navy stuff in your game, theyre probably useful in combination with subs and destroyers and battleships. personally i never got around to it since my basic naval strategy is depending on my available cash and opposing air power, either go for a ton of battleships or build submarines and get the supersub tech advance. personally i think AC are a waste of time, and a better use for your airpower is to go with the longrange aircraft and heavy bombing tech advances and bring down death from the skies simply by hopping between friendly land territories and blowing up land, air and sea unit all the way around. whatever thats my 2 cents.