In my sci-fi book, the Carballoon is a huge carbon balloon made mainly from graphene foam. (In a nutshell, graphene foam is made up of tiny graphene spheres with a vacuum inside to give an average density lower than helium.)
It has many civilian uses as described there, but is also useful militarily.
Some of the smaller balloons that it can send out would have reconnaissance or espionage functions. Some would have weapon systems on board, and having variable buoyancy, could sneak into an area at high altitude unnoticed before descending and bringing death from above. They could occupy some of the roles occupied by today’s drones, so would likely be covered by similar legislation.
Subject to that legislation, weaponry could include guns, directed energy or particle beam weapons, and graphene dart swarms, as well as missiles and bombs. These weapons would potentially scale with balloon size so that the mothership Car-Balloon would be very powerful.
The main advantage balloons convey is range and duration. They could stay afloat permanently without consuming power. They could sit stealthily for long periods on standby before being woken up to come into action. In fact, all the time they are afloat, the solar cells on the upper sections could accumulate energy and store it in graphene super-capacitors, to be released as required.
Graphene foam would be a very low density solid, so it would not fall if punctured. The pieces would stay afloat even if it were broken up. Self-organisation and assembly functionality could be distributed throughout the foam to allow pieces to come back together, and thus enable continuous self-repair.