Point of nuclear weapons on instant alert

The NPR is expected to state that the US will not use its nukes to attack a country that does not itself have nuclear weapons - as long as that country complies with the Nuclear Non-Proliferation Treaty - and it may renounce nuclear weapons as a response to chemical or biological attack. It may also say 2500 "spare" US nuclear warheads will be destroyed.

But it is not expected to pledge that the US will never be first to launch a nuclear strike, nor that nuclear weapons are only for deterrence or response to nuclear attack. This policy means that the US, along with Russia, will continue to keep 1000 to 1200 nuclear missiles "on alert". For those who support the elimination of nuclear weapons that is a cause for concern. "De-alerting is the key problem," says Ivan Oelrich of the pressure group Federation of American Scientists.

To deter or respond to an attack, nations don't need to keep weapons on alert, says Oelrich. No country could take out all US missiles in a first strike, so a reprisal would not need to be speedy. The only reason to have so many on alert would be to pre-empt a large imminent attack by Russia, says policy analyst James Acton of the Carnegie Endowment for International Peace, a Washington DC-based think tank.

Missiles on alert are a worry, partly because a malfunction could lead to accidental launch, or they could be hijacked - but mostly because they could be launched by misinformed or pressurised military leaders or politicians during a fast-evolving situation, Oelrich says.