By Angus Roxburgh BBC News Online, in Tisa, Czech Republic

On a bleak army training ground in the north of the Czech Republic, not far from the border with Germany, an army unit which less than 15 years ago was Nato's mortal enemy is practising for its role at the cutting edge of Nato's plans for the future.

Troops wearing green plastic suits and respirators swiftly erect a mobile "car wash".

NBC battalion is trained to deal with chemical attacks

Within half-an-hour it is ready to decontaminate up to 60 vehicles an hour.

Over on another field a team in bright blue suits, breathing heavily and loping around like spacemen, take samples for analysis, simulating the aftermath of a chemical attack.

Another team has put up a tent, with showers to decontaminate people caught in the assault.

Highest alert

The 500-strong Czech-led Nuclear, Biological and Chemical battalion will be part of the Nato Response Force (NRF), which is to be formally launched on Wednesday.

Our army was completely rebuilt and now we are trying to be the best army of all Major Vratislav Osvald NBC battalion commander

Planned to have 21,000 troops when it reaches full capacity in 2006, the NRF is the alliance's response to the challenges and threats of the 21st Century.

It will be a standing force, kept on the highest level of alert, ready to be deployed at just five days' notice, anywhere in the world, to meet threats from terrorists, mount peacekeeping operations, evacuate civilians or help out in natural disasters.

It will have its own dedicated fighter-aircraft, ships, army vehicles, logistics, communications and intelligence, making it self-contained and self-sufficient.

The decision to create the force was taken at Nato's summit conference in Prague last November.

An alliance created in the 1950s to defend Western Europe from the Soviet threat was faced with an existential crisis. The communist threat no longer existed, so why was the alliance needed?

Global reach

Its Secretary-General, Lord George Robertson, told the Prague summit: "Nato must change radically if it is to be effective. It must modernise or be marginalized."

The Czechs are happy to be seen as a key part of the new force

The solution was to create the Nato Response Force - described as "robust, readily deployable and credible". Its reach will be "global", not restricted to the alliance's traditional remit.

It is led by General James L Jones, the Supreme Allied Commander in Europe, who describes today's threats as "insidious and asymmetric".

Terrorist attacks around the world in recent years have persuaded Nato chiefs that only a highly mobile force like the NRF can mount an effective defence.

The Czechs, who provided chemical and biological defence in Kuwait during the war in Iraq earlier this year, are delighted to be seen as a key part of the new force.

If Nato is to be a stick for the United States to beat the Europeans into submitting to an American view of the world, then the alliance is doomed Sir Timothy Garden British defence expert

The battalion's commander, Major Vratislav Osvald, says: "The environment in our country has changed completely since the Berlin Wall came down.

"Our army was completely rebuilt, we changed our procedures and equipment, and now we are trying to be the best army of all."

Delayed decisions

There is one potential fly in the ointment. The force might be ready for deployment in just five days. But at the moment Nato takes all decisions - about deployments and other matters - by consensus. And that can take a long time.

Czech Deputy Defence Minister Jan Vana says it is the military's task to be ready for action as soon as the politicians give the signal.

Nato chiefs say only a force like NRF can mount an effective defence

"But politicians must also be ready to take action in just days," he says.

The arguments within Nato in the run-up to the US and UK's invasion of Iraq suggest that the NRF will only be able to be used in uncontroversial situations - at least for as long as Nato continues to take decisions by consensus.

There are many political and military figures in the US who argue that it is time to abandon the need for unanimity, which will become even harder to achieve when seven new nations join the alliance next year, bringing its membership to 26.

Critics in Europe fear that the US wishes to use the NRF as a sort of police force, to allow the Americans to intervene around the world by proxy.

"If Nato is to be a stick for the United States to beat the Europeans into submitting to an American view of the world," says Sir Timothy Garden, a British defence expert, "then the alliance is doomed."