Nato's Response Force, which has been formally launched at a ceremony in the Netherlands, has two main purposes.
As its name implies it is intended to be a standing pool of air, land, and sea units able to deploy to a trouble-spot at very short notice.
But it is also an important vehicle of transformation - a force for change.
It is intended to address one of the Alliance's main military problems; Nato has lots of soldiers but relatively few of them are actually trained, ready and equipped to be deployed beyond their own national borders.
You frequently hear stories that Nato countries are over-stretched; that operations in Bosnia, Kosovo and now Afghanistan are making life impossible for the armed forces.
There is no doubt that many units and specialists are over-stretched.
But it's not because of a fundamental shortage of service personnel.
Even without the United States' massive pool of manpower the 18 other Nato countries have some 1.4 million people in uniform. That's an impressive number.
With only a few exceptions, most Nato countries still find it difficult to despatch significant forces beyond the Nato area - and importantly - to sustain them once they arrive in a combat zone
But only about 50,000 of them are actually deployed on operations and the cries of "overstretch" are getting louder.
This is because many Nato countries have been slow to reform their armed forces in the wake of the Cold War.
There was a tendency to cut-back on numbers (probably fair enough) but also to stint on equipment spending, all in the search for a sometimes illusory "peace dividend".
Thus when it came to a real conflict in the Balkans, few Nato countries had air forces capable of delivering modern precision-guided weapons. Their land forces were trained and organised for territorial defence.
And with only a few exceptions, most Nato countries still find it difficult to despatch significant forces beyond the Nato area - and importantly - to sustain them once they arrive in a combat zone.
George Robertson, the outgoing Nato Secretary General, has made improving military capabilities the hallmark of his tenure. He has had reasonable results.
After much badgering, governments have slowly come to realise that there is little point funding military forces if they are not capable of being used.
The new Response Force is the centrepiece of Lord Robertson's reforms.
Soldiers of different nationalities will rotate through the force
Initially it will only be about 6,000 strong.
Indeed for the first few years the force will be something of an experiment, though it will be able to undertake missions if required. The aim is for the force to build slowly and to be fully up to strength by October 2006.
Within three years, the Response Force will comprise a naval task group, including amphibious forces; a brigade combat team of troops; and an air component capable of mounting two hundred combat sorties a day.
In total it will amount to some 20,000 personnel including all of the support services - the "strategic enablers" - like logistics, engineers and so on - that will allow it to survive and support itself once missions are under way.
The aim is for the force to be ready to go at five days notice - this, in military terms, is "the speed of light" as once senior officer told me.
Constant rotation will mean that troops from many countries will have to meet the stringent standards set for the new force
But the Nato Response Force will also act as an important catalyst for change.
National units will train and then be part of the force for some six months, after which other units will take their place.
This constant rotation will mean that troops from many countries will have to meet the stringent standards set for the new force.
Over time this will create a much larger pool of units, all with significantly enhanced mobility and equipment.
Nato spokesmen see the Response Force as capable of taking part in a variety of missions which could include:
disarming groups in a conflict
- acting as a show of force to deter aggression
- humanitarian support
- the initial entry element for a much larger deployment
It has taken a long time for Nato governments to appreciate the problems facing their armed forces.
But since the decision to create a Response Force was taken at the Prague summit in November 2002, the military planners have moved very quickly.
The initial Response Force is being activated one year ahead of schedule. Force planning is also under way for a quite separate expansion of Nato's activities in Afghanistan.
The alliance looks set to remain the only multi-national military player capable of deploying and sustaining forces either in support of its own political goals or those of the United Nations.