CALGARY -- The muffled thud of an exploding stun-grenade is the signal.

A handful of men silhouetted against winter skies swoop down the outside of a building, the crackle of rapid-fire machine guns piercing the billowing smoke.

The Royal Canadian Mounted Police, the world's picture-postcard police force, are rehearsing for their Olympic nightmare.

Armed to the hilt and with blackened faces almost hidden by balaclavas, the squads of highly-trained "Mounties" present a contrast to their popular image.

Six years of top-level training have turned their units into crack anti-terrorist forces.

The brilliant red tunics and wide-brimmed hats have been replaced by camouflaged clothing, West German-made Heckler-Koch MP-5 submachine guns and Swiss-made Sigsauer semi-automatic pistols.

But the men ready to hurl themselves into action in the name of security at February's Winter Games are no imposters.

"They are volunteers from the force, who, after training or exercises, return to their normal duties," explained Inspector Keith Thompson, Operations Commander for the mounted police's Emergency Response Teams (ERT).

"That could be plain clothes or uniformed. But they are called up whenever there's a crisis."

"Whatever situation develops in Calgary and whatever imagination you use to create the worst incident, I'm confident that we'll be able to deal with it," he added.

The Mounties began developing emergency teams about 10 years ago, but Thompson said the move was not a deliberate bid to toughen up the image of the Mounties, who are associated more with a horse than a hand-grenade.

"That's something which has been built up by the media and tourism," he said, adding that the government decided that the Mounties, not the military, should develop the emergency response teams.

"We made no big fuss about it. We just went ahead with it and did what we were supposed to.

"When the Olympics came along we had to escalate our training," said Thompson. "We had to increase our scenario of situations to ensure we were ready for anything."

Security has been a key concern at the Olympics since the massacre of Israeli athletes in Munich in the summer of 1972.

The core of the anti-terrorist operation for this winter's Games is based in Ottawa, home of the Special Emergency Response Team (SERT), which was trained by Britain's Special Air Service.

Thompson said the SERT is trained to deal with terrorist acts and has no direct role to play in the Games' security operation.

But the special team has helped train Calgary's ERT -- which Thompson called a "very specialized, highly trained unit capable of dealing with any situation" -- in various techniques used by the British air service.

Police chiefs will reveal few statistics about the Games' security operation, which is being shared by the Mounties and the Calgary Police Service at a reported cost of around $15 million.

The Mounties will be responsible for security at the Games' mountain sites of Nakiska and Canmore -- where the Alpine and Nordic skiing events will be held -- while the Calgary police will handle security at the city arenas and athletes' village at Calgary University.

There are no plans to involve the military in the operation, although 600 soldiers will be on standby throughout the Games ready to react if required.

The accent is definitely on deterrence.

Two senior officers -- Inspector Gord Shaw of the Calgary police and Mounted Police Superintendent Ron McIntyre -- have coordinated the operation which is based heavily on monitoring terrorist activity abroad and determining the risk of an attack in Calgary during the Games.

McIntyre believes Calgary will not be a target. "The probability of a major incident occurring here is very, very low," he said.

But nothing has been left to chance.

Inspector Gerry Befus, head of security at the village, said armed police would be positioned on rooftops at the village 24 hours a day. Hourly random checks of people in the village are also planned.

Police chiefs maintain the Olympics facilities and the host city will not be transformed into armed camps.

Security will be tight but not overpowering, they say, with around 1,000 specially trained volunteers assisting uniformed and plain-clothed officers.

The hub of the security operation will be a new command center at city police headquarters in downtown Calgary where cameras mounted at sports facilities and potential hotspots will feed banks of television monitors under constant watch.

In the event of an attack, computers will generate images showing exactly what police are likely to see if they have to burst through a specific door or window.

Every site, including hotel rooms occupied by dignitaries, will be searched regularly for explosives and no athlete, International Olympic Committee (IOC) official or senior government leader will step into a vehicle before it is swept for bombs.

And squads of Mounties will patrol the mountain sides on skis and snowmobiles and also protect a smaller athletes' village in Canmore.