An AA Gun only fires once per combat - in the opening fire step of the first cycle only. It has been this way (with different terminology sometimes but essentially unchanged) in Classic, Pacific, Europe, and Revised, both OOB and LHTR. Never any different.
And leaving that DST alive and the Suez open invites another problem…
A pretty nice UK fleet roaming the Indian Ocean. By UK2 it can be 2 DST’s, an AC, 2 FIGs, 2 TRNs and a sub. That puts them on par with Japan’s remaining fleet after Pearl…