A balloon is an unpowered gas-filled container which remains aloft or floats due to its oveall buoyancy. A balloon may be free, moving with the wind, or tethered to a fixed point.
The military of the Empire of Charis began using fixed balloons filled with hydrogen as lookouts in the Year of God 989, greatly increasing their information gathering and battlefield coordination abilities. They were usually manned by a two-man crew that interacted with a dedicated surface counterpart through messages sent up and down along the line holding the vessel. (AST)