I read few great articles:

https://en.wikipedia.org/wiki/History_of_military_ballooning

https://www.britannica.com/topic/Balloon-Corps

https://en.wikipedia.org/wiki/Zeppelin

My conclusion:

All are land units, but giving air recon. Aerodrome is not required to build and develop.

Units give better recon visibility including higher positions. Very helpful for siege units.

Balloon (early Industrial Era) - unarmed

Zeppellin (late Industrial Era) - can defend

Drone (late Contemporary Era) - can defend and attack

PS

Or simplified version without Zeppellins:

Balloon (Industrial Era / Aeronautics tech) - unarmed

Drone (Contemporary Era / Jet Fighters tech) - can attack

PPS

Turkey emblematic unit could be changed from Stealth Missle to Stealth Drone!