Fast firing AA guns rely on the Reload sailor stat, and the guns' reload speed stat.
Get anything that has base 12 reload, even 7/12 is usable. Class nation, then Arm sailor and do not class to AA immediately because that kills the reload stat (it increases AAW only, which is disabled in sailors).
Continue to delay class up to level 70~120 and you will have a nice UK AA gunner. While levelling it, you can use the sailors as HH operators.