And that has added to the frustration over, for example, Mr Putin's backing for Syria's government or a senior Russian general's statement that the country did not rule out the possibility of a nuclear first strike against missile-defence sites.

ECONOMIST: Russia and America

The first is that although the West is safe in the sense that the existential threat of invasion by a malevolent foreign power or a first strike by a nuclear-armed aggressor is now vanishingly small, the rise of jihadist terrorism has left people feeling vulnerable.

ECONOMIST: Weighing safety against liberty

If they do not, their own military men will spend an increasing amount of time worrying about the danger of losing all their nuclear might to an enemy's first strike.

ECONOMIST: The ostrich��s view of the world

Thus, the U.S. has sought to organize its nuclear forces so that no enemy can launch a disarming first strike, mainly by fielding three distinctly different types of weapons: manned bombers, land-based intercontinental ballistic missiles in hardened silos, and sea-based intercontinental ballistic missiles on stealthy Trident submarines.

FORBES: Nuclear Weapons: How Few Is Too Few?

They are the only nations that both possess nuclear weapons and are large enough, in theory, to absorb a first strike and live to retaliate.

CNN: ASIANOW - Asiaweek | Intelligence | Japan: Self-Destructing

Talks are continuing to try to avert the first ever strike at the firm that builds warheads for Trident, the UK's nuclear weapons system.

BBC: Talks continue over nuclear warhead workers' strike