As the Obama administration considers whether to send more troops to Afghanistan, Michael Codner, director of military sciences at the Royal United Services Institute, weighs up the US president's four options.
Deploying another 40,000 troops is the option pushed for by the top US military commander in Afghanistan, Gen Stanley McChrystal.
He is in charge of both the Nato International Security Assistance Force (Isaf) and of national US forces in Afghanistan (under the label Operation Enduring Freedom).
Gen McChrystal supported this request in a leaked assessment. In this, he explained the need for a new strategy for Nato, which included winning a "short-term" and a "long-term" fight.
The short-term fight entails regaining the initiative from the Taliban.
Winning or losing
The outcome of the short fight will be decisive - a key word in military doctrine because it defines a particular type of operation which can actually be won or lost.
The US public is growing weary of Afghanistan after eight years of war
And he says the short fight must be won in 12 months.
So the 40,000 he has asked for is very much a surge against the Taliban specifically and the troops need to be put into theatre soon.
The long fight will be an operation of a different kind in which winning or losing is not the issue.
Rather US and coalition forces will at some unpredictable stage in the future be able to leave Afghanistan as a nation able to manage its own security through development of security forces (the Afghan armed forces and police).
Britain's Malayan campaign
To win the long fight, Gen McChrystal calls for a change of operational culture focusing on the Afghan people rather than territory, force protection and other tactical war-fighting considerations.
A surge of 40,000 is a significant figure.
If the numbers of other coalition forces remains, constant the total number of intervention forces in Afghanistan will approach the level, in terms of troops-to-territory ratio, of one of the few previous decisively successful counter-insurgency operations: the British in Malaya against the Communist insurgency of the 1950s.
Will Nato take some of the strain by pitching in with extra troops?
Now one of the only enduring insights from the history of counter-insurgency is that each campaign is unique.
There are no enduring principles. And crude figures mean little.
The actual capabilities they represent, unity of command (one of the requirements Gen McChrystal mentions), the competence of local forces, integration of non-military instruments and political outcomes are all so important.
But it is not an irrelevant benchmark.
It bears mention that an equivalent troops-to-population ratio to the Malay campaign would be about 15% higher.
And the troop levels that contributed to stability in Bosnia and Kosovo were vastly greater.
For the UK, the question would be what proportion of these forces would be committed to Helmand to relieve British overstretch.
The UK typically has been reluctant to bargain over its responsibilities with the US and is inclined to follow the mantra "tell us what to do and by God, we'll do it" - noble, but an aspiration too far.
The 30-35,000 soldiers option said to be favoured by Defence Secretary Robert Gates and the Chairman of the Joint Chiefs, Adm Mike Mullen, needs to be seen in context.
The rumour is that Mr Gates and Adm Mullen do not disagree with Gen McChrystal's 40,000 plan, but that they expect Nato to come up with the additional 10,000.
So, the new strategy is still valid but Europe must cough up.
The problem is that the war is seen by most coalition partners as one initiated for good reasons by the US in its direct national interest, with the removal of the Taliban government, and that the US bears responsibility for seeing it through, notwithstanding the distraction of Iraq.
The Bush administration wanted a US-led, not Nato-led, campaign in 2001
After the 9/11 attacks, Nato members for the first time in history invoked Article V and offered their support to the US in a matter of collective self-defence.
But the Bush administration rejected proposals for a Nato-led operation against the Taliban in 2001 in favour of a US-led campaign in support of Afghanistan's anti-Taliban Northern Alliance.
One could say that the present Nato operation was one of 'helping out' the US, rather than a Treaty obligation.
The troop levels of individual European nations are a matter of how they see themselves in relation:
• on the one hand in their own strategic bargain with the US for security in the global and European contexts
• and for some countries, their moral obligation as wealthy nations to the Afghan people
These are not motivators for increasing troops levels, particularly in the present economic crisis. The US cannot offer 30,000 as some sort of a bid to Nato to push numbers up.
To settle for 20,000 extra troops would mean President Obama has dismissed Gen McChrystal's demand for a surge in favour of specific roles and missions, perhaps specifically in the form of specialist forces targeting terrorism, or in separate roles in developing Afghan security capability.
There would need to be yet another new strategy and this must come from the US, not from Nato.
The fourth option is rumoured to be 10-15,000 extra troops.
This relatively small number could of course be an attempt to bounce President Hamid Karzai in to sorting out his own government and eliminating corruption.
'All you're getting'
It might open the door to further troop increases, but would send the message: "This is all you are getting unless there is some real change in the culture and organisation of the government."
Will any extra troops come under Nato or under US command?
The actual roles and missions of this number is anyone's guess.
Of course strategic options are not just a matter of troop numbers.
The other factors are roles and missions; the actual timelines for deployment and whether they are surged or deployed incrementally; how they are dispersed geographically; and finally their command and control.
Will they be part of Isaf or under US national command in Enduring Freedom?
The four options may not be a ladder of numbers but a combination of numbers and some or all of these other factors.