They're actually very commonly used, particularly in Afghanistan: http://www.nytimes.com/2012/05/13/world/asia/in-afghanistan-spy-balloons-now-part-of-landscap

They're actually very commonly used, particularly in Afghanistan: http://www.nytimes.com/2012/05/13/world/asia/in-afghanistan-spy-balloons-now-part-of-landscape.html?_r=0 http://www.nytimes.com/2012/05/13/world/asia/in-afghanistan-... The motivation is twofold. First, they don't require fuel to loiter - or, in the case of a hybrid like this, they only need to keep going at a very low speed to get enough lift to stay aloft. Second, as long as the filler gas isn't flammable and you have a half-way-decent self-sealing liner, it's actually quite hard to bring one down - rifles and most cannons poke pretty small holes in a balloon, so the rate of loss of buoyant gas would be quite low, and a flexible balloon deals with the overpressure wave of high explosives better than a rigid structure. (See the last part of that news article, where they mention the balloons coming down for periodic servicing with hundreds of bullet holes in them, yet still perfectly functional.)