There are no AA-specific guns for the RM. Until your gunners get up to a level where they can reload rapidly on their own, the fastest loading gun is the 5"/38 Mk 12.

I was reading and watching bbs spaces and weapons. so note that only 2 or 3 bb could use the 5 "/ 38 Mark 12 (space 67). hopefully do something about it because these are the best I have seen for aaing

 5"/38 Mk 12 could be a nice AA guns, but have a size of 67.
So, maybe can be a nice AA gun but it can be fitted only un BB4 to BB6. That have no sense.

Maybe is time to post a suggestion for:
- Reduce   5"/38 Mk 12 to fit it in BB2 or 3
- Reduce AA bind size, to load enough AA ammo
 

I been playing RM for a long time and there are lack of AA gun displacements in every class (except CVs).

The fastest AA gun in RM will be 5"/38 MK 12. But overvets and turn them in prem. sailors will be able to fire faster on 5.3"/45 Model 1938 or possible 6"/55 Model 1936. The problem for RM will be lack of power on AA guns and there is no AA gun specification.

RM AA gunning range will be in US to KM. Not very far enough to consider similar from MN AA guns. 

RM 5"/38 MK 12 can kill Low level plane about 4-6 shots. 5.3/45 Model 1938 About 2-4 shots. 6"/55 Model 1936 possible 1-3 shots in lowest plane level.

This conclusion RM AA guns aren't good in game since of their low quanity T-slots. (Except CVs). 

IMO. again MY OPINION. RM be better with HH guns since its a rushing nation. AA for RM blows. Go HH setup imo. better for rushing