The technicians, analysts and generals at the North American Aerospace Defence command (Norad) are the keepers of hundreds of military secrets, but perhaps the most closely guarded is how they manage to track Santa's flight path every Christmas Eve.

Friday will be the 55th year that the joint U.S.-Canadian defence warning network has followed Santa on its radar screens -- and posted minute-by-minute updates on the Internet for children around the world.

But Norad insiders are coy about how exactly they can so closely follow the movements of one jolly old man in a sleigh drawn by tiny reindeer.

"We use a system of radars spread across northern Canada and Alaska. We also have a system of satellites which are hundreds of thousands of miles above the earth," Canadian Lt.-Gen. Marcel Duval, deputy commander of NATO, told CTV News Channel. "The same technology, as we found out 55 years ago, is also useful to track Santa.

Norad officers will only say that Operation Norad Tracks Santa -- the official name of the military mission to follow St. Nick -- uses a combination of "ultra-cool, high-tech, high-speed digital cameras," radar, satellites and Canadian Forces fighter jets.

Questions about the technical details are met with a polite rebuff and a cryptic explanation involving the magic of Christmas.

Duval would offer only one hint: "The giveaway for Santa is the red nose right at the front end of his convoy, if you will."

Norad, established during the Cold War to track incoming Soviet aircraft or missiles, began following Santa in 1955 after a Colorado newspaper published a phone number for local children to call for their Christmas list to Santa and to get his current location.

But the newspaper printed the wrong number, instead listing the number for Norad's command post, which was quickly flooded with calls from curious children.

"The individual on duty that night … decided to just go along with the first phone call, and indicated to the kid where Santa was," Duval said. "And throughout the night they kept getting calls, so that was the start of it."

It has since become a cherished tradition at Norad, the joint U.S.-Canada command first established during the Cold War to watch for incoming Soviet bombers or missiles from its control centre at Peterson Air Force Base in Colorado Springs.

The Santa exercise takes four months of planning, 1,200 volunteers, 100 telephones, 30 laptops and two big projection TV screens.

Volunteers wearing blue Santa hats emblazoned with "Special Operations Elf" answer calls in two-hour shifts while others fire out tweets and Facebook updates, checking against a schedule marked with a secrecy warning that said "Santa's Eye Only."

"It is tremendously fun," said Jim Jenista, NORAD's deputy chief for joint training exercises who has volunteered to answer the phones for nearly a decade.

Last year, they answered 74,000 phone calls and 3,500 emails from around the world asking for Santa's location.

More than 13 million unique visitors went to the Santa Tracks NORAD website last December. NORAD Tracks Santa had more than 512,000 "likes" on Facebook by Friday and more than 37,000 followers on Twitter.

The Norad Santa operation also has a Youtube channel, apps for mobile phones and the phone line, 877-HI NORAD.

Duval said the volunteers try to be vague about Santa's exact itinerary and time of arrival, but added helpfully: "He'll arrive on the coast of North America sometime tonight around 9 p.m., or 2100 hours, so by then the kids should all be in bed if they want their presents."

With files from The Canadian Press