A swift, powerful air strike can be an invaluable tool for U.S. military forces in battle, so long as it gets there fast enough, and the Department of Defense is developing just the aircraft for the job. The Defense Advanced Research Projects Agency (DARPA) and the United States Air Force (USAF) are seeking contractors to build an unmanned hypersonic aircraft capable of reaching any point on the world map in about two hours. Though initially a creature of war, such an aircraft could eventually serve as a springboard into space, developing technology that could lead to a single-stage-to-orbit spacecraft. The...