Well, I’d agree with you that buying a single naked BB rarely makes sense – BBs are strongest when they can be used as the capstone of a larger, more diverse navy.
I’ve been known to buy CA + DD for the Brits in Anniversary, where the British fleet can just project monstrous power out of the English Channel – you’re threatening France, Norway, Berlin, Poland, etc. all from the same sea zone, and many of those territories come with large national objectives attached.
And in a social game of Balanced Mod Global, where I’m aiming to have fun more than I’m aiming to win, I could see buying CA + DD + Marine for Italy or Australia, just because Marines are a cool unit, and sometimes your economy means that you can’t afford a second loaded transport, but you can afford one loaded transport plus one marine, and that extra oomph will get you over the finish line to take Cairo or Singapore or whatever.
In Classic Global, though, I just don’t see it – if there is enough of an aerial threat that you need the DD+CA at all, then you probably need a massive fleet that includes at least one fully loaded carrier, and if you don’t have the cash to drop that fleet all at once, then it’s better to save up for a turn and buy the fleet next turn.
