The first use of aerial vehicles on the battlefield was balloons hoisted up into the to spy on enemy troop movements, and occasionally to drop bombs. Balloons were used in the American Civil War, and even during the French Revolution, though in recent decades emphasis has shifted towards jets, rather than balloons.
But that may be about to change. The U.S. Air Force is looking into a high-flying, solar-powered blimp to take over spy duties, and say a small demonstration prototype could be in the air by 2014.