Pat
Three Thousand Club
X-01s were around during the Great War. The Secret Service had them. For some reason there's a few in Boston. But they're not the same as Hellfire power armor.Pat A series of prototypes were developed shortly before the war, X-O1s.
X-02s didn't even exist until roughly 2242.
X-03, or Hellfire power armor, didn't exist until very roughly 2277. It's a postwar design based loosely off the X-01.