The Pentagon is seeking to develop a drone in the next two decades that could strike any spot on earth from the continental United States within two hours. The so-called Hypersonic Cruise Vehicle, which would be designed to hit targets about 9,000 miles away, should be available by about 2025. ("Hy-personic" means traveling at more than five times the speed of sound.) The photo shows a hypersonic cruise missile engine during testing at NASA's Langley Research Center in Virginia. (NASA/Reuters)