The US will slash its stockpile of nuclear weapons by nearly half over the next eight years, the US Department of Energy has pledged.
Reductions to the nuclear stockpile would leave the US with "the smallest nuclear-weapons stockpile we've had in several decades", said Linton Brooks, administrator of the National Nuclear Security Administration, on Thursday. He would not discuss exact numbers, but told the New York Times: "The numbers I'm prepared to use are 'almost in half'."
The move is in addition to the existing pledge made by US President George W Bush under the Strategic Offensive Reductions Treaty in November 2001. Also known as the Moscow Treaty, this commits both the US and Russia to cut the number of "operationally deployed" warheads to between 1700 and 2200 by 2012. This will mean a cut of two-thirds for the US.
However, the real extent of the nuclear weapons reduction is difficult to gauge as weapons are classified in a number of ways. Reducing the number of operationally deployed warheads could mean reclassifying them as reserve weapons, dismantling them and storing the components, or less likely actually destroying them.
"It's certainly a welcome step," says Matt Martin, deputy director of the British American Security Information Council, in Washington DC. "Any time the US administration announces it's going to be making a reduction is a step forward - it's better than doing nothing."
But he points out that there are many questions yet to be answered about the plan, which was sent to Congress in a classified report on Tuesday.
"The first question is whether this is going to lead to an actual reduction in the US stockpile. I'm not sure that's absolutely the case," he told New Scientist. "The counting methods are so obscure, it's difficult to say exactly what the implications are going to be."
The nuclear stockpile can be divided into active and inactive weapons. Active weapons included operationally deployed warheads - which are attached to a delivery system such as a missile and are ready to use - as well as warheads separated from the delivery vehicles in "hedges". Inactive weapons can have their crucial components removed and stored.
Another question, says Martin, is the international context in which the US will keep this new pledge. Storing nuclear materials in countries like the US or UK does not pose a large security risk in terms of terrorists, he says, but this is not the case for Russia.
"The whole point of the treaties enacted throughout the Cold War period was that there was a reciprocal arrangement between the US and Russia, which had the great benefit of reducing Russia's stockpile," says Martin. He says the US would be better to use any willingness to give up nuclear arms as leverage to persuade Russia to do the same.
Martin also points out that eight years is long enough for the Bush administration to push ahead with plans for creating new nuclear weapons or modifying old ones.
The current large and massively destructive weapons are not considered to be particularly useful in today's climate, he says, and projects for creating "mini-nukes" have been touted. On Wednesday, the House of Representatives voted not to remove a clause in a defense bill that provides funding for research on nuclear "bunker busters".
Brooks' covering letter to Congress also highlights that: "In recommending this stockpile plan to the President, we recognise that maintaining the nation's nuclear deterrence with a much smaller stockpile means that we must continue administration efforts to restore the nuclear weapons infrastructure."
This includes plan to build a new bomb plant. This Modern Pit Facility would manufacture the "pits" which form the central core of plutonium weapons.