How about making AA guns transportable (is that a word?). -- i.e. they can be transported at the capacity of 1 aa per transport. Also, when the transport is attacked while the aa gun is loaded -- the AA gun fires as usually. The AA may not be taken as a casualty ... and if the transport is sunk -- so too is the AA. This is similar to the W@W rule (I think?).
This gives AA guns an added feature ... and allows an added method of protecting your transports and other navy units.
I think that is how 1st Edition rules go too...