The Campaign covers anything that is broadly classed as a staff car - used primarily to ferry officers and VIPs around, often (but not always!) well behind the Lines out of earshot of the shooting. See Rule 1 for an idea of the rather wide range of subjects that'd qualify!
The Rules and Regs
1) Can be any nation, scale, or era, and can include Jeeps, cars, well-known "General's Rides" like Patton's White Scout Car or Rommel's halftrack, or even an old-school General on his favourite horse! (Pharoah on his chariot take your fancy?...)
2) No "command tanks" - these are essentially fighting machines.
3) Accompanying figures are encouraged, as is the gratuitous use of gloss paint and conspicuous markings!
4) Oh, and if you want to pass that staff car off into private post-military hands, that's cool too. Many of the kits out these days started as civilian cars anyway. And "borrowing" by the enemy is fine too - Rommel used an AEC Dorchester in the desert, and many German staff cars got recycled by the Allies.
5) Must post a "before" shot of the kit parts or box before starting the build, followed by at least one "in progress" shot in the thread (a running set of photo updates is encouraged), and at least one completed shot in the campaign gallery. Models must not be started before campaign starts, but if used in a diorama they may be coupled with other figures and vehicles that you already have finished.
6) Having fun, offering comments & advice, starting Build Logs, and other acts of Conspicuous Comeraderie are strongly encouraged!
Each person who successfully builds at least one qualifying model and posts photos as per the rules will get a ribbon for their Profile page. One ribbon per person regardless of how many models they complete, but multiple builds are still welcome.