Hypersonic Cruise Missiles
The U.S. is developing a weapon capable of striking anywhere on the planet within an hour. The article talks about the possibility of modifying Trident missiles—problematic because they would be indistinguishable from nuclear weapons—and using the Mach 5–capable X-51 hypersonic cruise missile.
Interesting technology, but we really need to think through the political ramifications of this sort of thing better.
EDITED TO ADD (5/13): Report on the policy implications.