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.