In addition to defusing mines, restoring bridges and returning refugees, they face the potential hazards of Nato's own unexploded bombs and Serbian paramilitary snipers.

Operation Joint Guardian aims to pour the 48,000 troops of Nato's Kosovo Force (K-For) into the province as quickly and extensively as possible within hours of a Yugoslav withdrawal.

Lieutenant Spencer Ainsworth (2 Para): "We're highly trained for this sort of thing"

It is considered vital that K-For does not allow a "power vacuum" to develop which could be exploited by the Kosovo Liberation Army (KLA) or Serbian irregulars opposed to the peace plan.

Ian Kemp, a land forces consultant with Jane's Defence Weekly, said "the KLA needs to be disarmed" in order to prevent reprisals or fighting as the Yugoslav forces pull out.

Engineers make up a large contingent of K-For

He told BBC News Online: "There is a sizeable minority of Serbs in Kosovo and they need to be protected from Kosovo Albanians who may be keen on revenge."

How Nato will deal with the KLA remains unclear.

Speed is also essential to deliver humanitarian aid to the many thousands of Kosovo Albanians who are believed to be displaced within the province.

The majority of K-For troops are expected to enter the province from the Former Yugoslav Republic of Macedonia and immediately take control of key "command positions" inside Kosovo.

Minefields and bombs

Crack troops, such as the UK's Parachute Regiment and Gurkha Regiment, will spearhead the operation, backed by tanks, armoured vehicles and Apache attack helicopters.

K-For is responsible for returning refugees

The UK is contributing the largest contingent of troops - 13,000 - with another 6,000 on standby. The United States, Italy and France are also sending large contingents, with other Nato nations contributing up to 1,000 troops each.

In addition, 10,000 Russian troops, whose exact function is unclear, are also to be committed to Kosovo.

Engineers, or sappers, make up a large body of the multinational force. They are set to play a key role in all phases of any Nato operation in Kosovo.

Combat engineers will tackle unexploded Nato bombs and liaise with Yugloslav forces to make safe minefields on the borders of the province.

Their role also includes restoring the basic elements of Kosovo's ravaged infrastructure by clearing roads, building bridges and restoring communications.

Refugee safety

Support engineers will be setting up camps for the largest Nato ground force yet committed to the Balkans, ensuring essential facilities such as electricity and water supplies for bases that must last through the summer and the following winter, if not longer.

Apache helicopters help "overmatch" snipers

Nato will also be responsible for guaranteeing the same facilities for refugees as they return to the devastated towns and villages of Kosovo.

Non-governmental agencies like the Red Cross will play a major role in directing the return of refugees to their homes, but K-For is primarily responsible for the relocation and safety of the civilian population.

Villages and towns must be cleared of booby traps, while military vehicles will be needed to transport the refugees back.

Nato casualties

During the operation, K-For troops will be at risk from Yugoslav paramilitaries who may decide to stay in the province and harass Nato.

A principal concern of Nato commanders throughout the Kosovo crisis has been to limit the alliance's casualties. It is during this phase that alliance personnel will be most exposed.

Yugoslav snipers caused a major problem for the lightly-armed United Nations Protection Force (Unprofor) in Bosnia.

But Nato is confident that such paramilitaries will be "overmatched" by K-For's ability to respond.