March 20, 2010 -- In the next few weeks, President Barack Obama will publish his delayed Nuclear Posture Review (NPR), setting out the role nuclear weapons play in US defence.
This is Obama's opportunity to end one of the most dangerous legacies of the cold war: the nuclear missiles the US and Russia keep ready to fly in minutes. The signs are that he is unlikely to take it.
This leaves the questions why does the US keep its nuclear weapons "on alert", and are they really needed?
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 worrying, 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.
This is a particular risk in Russia, which still relies on ageing Soviet-era radar and satellites to scan for incoming missiles. In 1995, the Russian military briefly mistook a Norwegian weather satellite launch for an incoming missile.
To avoid such mistakes, Russia and the US have opened a monitoring station in Moscow to observe each other's missile launches. To minimise the consequences if an accidental launch does occur, Russian and US missiles on alert are now targeted at the mid-ocean.
Missiles can be taken off alert by screwing down switches or removing parts, so that it would take hours or days to launch them. But as these alterations cannot be observed by the other side, this will not induce them to stand down as well.
One way to make verification easier would be to keep warheads and missiles in separate buildings, as China already does. With this arrangement, any assembly work could be spotted by satellite.
Weapons on alert risk more than a US-Russian stand-off. At a meeting in May, non-nuclear nations may decide whether to continue obeying the Nuclear Non-Proliferation Treaty, which calls for nuclear nations to disarm. If the US says it still needs nuclear missiles ready to fly, they may feel they need them too.