Forum:Categories

why Red Alert category and articles begin by RA2? for example: RA2:Kirov Airship? why need RA2 at the begining? if trying find with search key: Kirov airship, you get: There is no page titled "Kirov airship". and why in "Category:RA2:Soviet GWWII Arsenal" all articles have RA2 at the begining, although they are from RA1?