There's an entire sticky dedicated to this discussion...

Baltimore's not bad either with the 1.08 rld guns on her T slots.

I'd rather DDX then them all

Ohama is fun AA CL and 7" singels make it deadly plus with one of the fastest CL
engines in the game Its sad no one uses it, because its alot easier the Atlata
however if you do Atlanta the Juno2 is the best because of the AAW boost!

-Fox

If you don't have a Pensacola, then I'd have to go with Atlanta with 5/38 mark 38L's:

http://trainworld.us/NF2/AA_Gun/AA_USA.html

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USN AA Ship does not exist

6" DP Guns A variant on the Monty.

Oh wait...

mwah I like the pensacola as an AA ship too.

Omaha with 3"/70s is the cheapest to equip.

Cleveland with 6"/47 DP L on the R-slots and 5"/38 Mk 38 D (or 3"/70 D if you are into
that sort of thing) on the T-slots. It takes some care to know when to switch, but this
gives you both high damage long range AA, and good damage fast firing close in AA.

That said, a Brooklyn with 6"/47 DP L on the R-slots and HH on the T-slots is a lot of
fun. (and ammo isn't an
issue. Weight can be, though.)