By way of Wired's gadget blog (which I usually don't have time to read, but someone brought this entry to my attention.) The military is working on a next generation weapon: a high altitude mirror that can bounce deadly laser beams down to targets over the horizon. The mirrors might be on high-altitude blimps or robotic airplanes. The mirrors apparently work with a giant airbourne laser carried by a 747.
What's interesting about this stuff is it's playing just beyond the edge of technology. It's kind of like the ironclads during the American Civil War that were designed to attack river fortifications. They were really pushing the state of the art in many ways, so you wound up with problems like the Monitor's steam-powered turrent continuing past the aiming point, making it more accurate to aim the main guns by turning the whole ship rather than the turret, or the deck being ripped off when they tried to weather too nasty a storm at sea.
In this case, it's a design that only makes sense if you have a really heavy, Expensive Giant Laser and relatively cheap platforms for mirrors. That way you can put your E.G.L. in a safe place and bounce it off your mirrors to hit things, replacing the mirrors whenever someone pops the balloons carrying them. After all, if your laser were cheap and lightweight, you'd just put it right on the balloon and be done with it. This approach also means you're stuck fortifying your E.G.L. to protect it. Which will probably work.
At least until someone builds the first "mirrorclad".