THE torrential rain finally lets up and the exhausted troops are having a laugh and a joke.

It's hard to believe that within minutes they are going to be attacked with a nuclear, biological or chemical weapon.

This is BATUS, British Army Training Unit Suffield, the biggest and most advanced battle training programme on earth, and the closest thing to a war.

It involves more than 1,000 troops and 600 vehicles firing ammunition worth $28m (Canadian), or £14m, on a deserted Canadian Prairie the size of Wiltshire.

The grassland prairie is immense - a rolling landscape which carries on, unbroken by signs of life, into the horizon in every direction.

It takes an hour of slippy off-roading to find members of the reconnaissance team who are shortly to be attacked.

They had already been gassed once that day, and know they have only nine minutes to get their environmental suits on after the alarm goes up, or they will be "killed" again.

The nuclear, biological or chemical weapons are simulated on a high-tech computer system, but the tanks and the weapons the soldiers carry are very real.

Sound travels across the empty space and the roar of the mighty Challenger 2 tanks can be heard long before they are seen.

The weather out in the prairie also defies any sense of logic.

Not only has the torrential rain of the past few days turned the dirt tracks, optimistically called roads, into sludge, but over the year the temperature yo-yos from minus to plus 40C. On the first two days of the exercise it turned overnight from blazing warm sunshine to snow.

But then, it's not supposed to be easy.

BATUS is the culmination of three years of training and puts into practice everything the soldiers have been taught to make them ready for war.

However, this year's BATUS nearly did not take place, and it was not because of Iraq, but because of the firefighters' strikes.

"This is a training year for us and it should have started in January but because of the firefighters' strike we were three months late," said Lieutenant Martin Ryan, one of QRH's admin officers.

"We found out three days before we left that we would definitely be going to Canada."

The 33-day course, in which the troops survive on the prairie with no creature comforts and three boil-in-a-bag meals a day, begins with a basic training refresher.

It then moves into a live ammunition exercise, attacking both static and moving targets.

"Some guys will have never fired live ammo before," said Lt Ryan.

"There are exercises in Germany but the tank mileage is limited, so this is often their first time and it can be very nerve-wracking."

The second element of battle is the simulation, which will be the focus of another feature.

Because BATUS is such a large-scale event and provides an opportunity to use live ammo, for many it is a rite of passage.

"The guys are very keen to get on the tanks and do what they were trained for," said Sgt Gary Bond, who has seven BATUS operations under his belt.

As quartermaster, Sgt Bond has the logistical nightmare of kitting out the 1,000 soldiers.

"BATUS is a baptism of fire," he said.

"It is as near to war as you are ever going to get."

But a realistic war environment comes at a cost.

Handling the tanks and ammo creates a risk of injury, and BATUS is no exception.

"So far we have had 28 serious and non-serious injuries, which is a seriously low proportion," said Lt Ryan.

Incidents have ranged from soldiers coming down with chest pains to others falling off tanks or getting limbs caught in the rapidly rotating mechanics of the tank.

But so far, everybody injured is expected to make a full recovery.

But in previous BATUS' exercises, other soldiers have not been so lucky.

"People do die, but the majority of these are road traffic accidents." said Lt Ryan.

"Safety is a big thing here and everyone is conscious of it."

The scenario of the battle is simple. The QRH Battle Group takes on the role of the blue team and performs a selection of missions culminating in a dawn raid on the enemy, the red team.

The enemy is made up of Op 4, soldiers from Royal Dragoon Guards and the Royal Regiment of Wales.

"They don't know it yet, but they did extremely well," said Colonel Andrew Cuthburt, who commanded the blue team.

"They are now battle-ready and if there are any problems anywhere in the world they would be the first ones in," he said, moments after the final battle of the exercise.

"They are now the most battle-ready regiment in the British Army."

Although no plans have been formalised, the general feeling is that the QRH will be posted to Iraq for six months in November.

"It would be as a patrol presence and to rebuild the infrastructure, not as aggressors," Lieutenant Ryan said.

But for now, QRH will return to Germany and if trouble flares up anywhere in the world, they will be on the front line.