Air Lord, Engineering Corps
Here's a suggestion to make for a more interesting campaign.
Forts are old abandoned buildings that can be found around the campaign map and can be taken over like cities, providing a no enemy fly zone around nearby allied cities and blocking landship roads until destroyed as long as the initial restoration cost and upkeep is paid for.
Forts also randomly appear in combat away from cities as a 'neutral' faction that is instantly claimed when entered by crew.
These types of random forts are usually damaged buildings of a random unique design that appear in the centre of the map, and are often quite large. Some may even require a dedicated capturing ship in the fleet to fully man.
On rare occasion they can sometimes be designs from times forgotten, examples range from small rotting tribal forts armed with ballistae to advanced clockwork fortresses with their own airship drone hangers and high penetration rail-spike launchers (fortress only large arc, high rate of fire AP guns). Some of the latter designs are sometimes still functional and fully automated, providing an additional hazard to all participants in the battle.
Thats a pretty good idea...
By the way... Could you post something that demonstrates what the airship drones would look like? I'm very interested to know...