Over time, the nuclear- weapon states have learned to manage command and control problems somewhat better than they have done in the past. Weapon security has been improved through better locks on warheads, and weapon safety improved by better design, including use of insensitive high explosives. Even attack assessment has been improved: as I understand it, two independent sources, relying on two different physical principles, are now required to verify that a nuclear attack on the US is underway. – The Strategist Photo: Steve Jurvetson – Creative Commons Attribution 2.0 Generic