To upgrade your Airship Dock, you need Navigation Compasses.
With each upgrade, you need more Navigation Compasses.
Below is a list of possible ways to gain these.
Gems
You can purchase Navigation Compasses using gems.
1 Navigation Compass = 15 Gems
10 Navigation Compasses = 125 Gems
100 Navigation Compasses = 1,154 Gems
1000 Navigation Compasses = 10,000 Gems
Campaign Elite Sweeps
You can sweet elite campaigns to pick up extra Navigation Compasses.
Elite 4-1
Elite 4-2
Elite 4-3
Elite 4-4
Elite 4-5
Elite 4-6
Chests
Chest from the VIP daily clan gifts (Steambeards city) gives Navigation Compasses too.
VIP Daily Clan Gifts
You can collect 5 Navigation Compasses per gift from daily VIP Clan gifts (Once you have level 25 diplomacy for this city).
Regular Events
Every 3 hours, you can do a regular event (Have to complete all 3 stages of it).
You gain 20 Navigation Compasses each time you complete it.