FORT COLLINS, Colo. – The red phone wasn't supposed to ring.

It was 1955, during the Cold War, and the menacing phone – perched in the Operation Center at Colorado Springs' Continental Air Defense Command (CONAD) – was Air Force Col. Harry Shoup's direct line to the Pentagon.

Only he and a four-star general knew the number.

"If that rang, it wasn't good news," Shoup's daughter Terri Van Keuren recalled.

But in December 1955, the red phone rang.

Shoup answered – "with his proper military voice," Van Keuren said, before lowering hers into a deep, gruff impression: "Colonel Shoup!"

"And this little voice says, 'Are you Santa Claus?'" she said. "And Dad is now, he's pissed. He thinks one of his staff is playing a joke on him."

But the call was real.

After realizing the caller was a child, Shoup put on his best Santa voice and saved the situation. He then talked to the child's mother, who asked: "You haven't seen the newspaper?"

A Sears ad printed in that morning's paper advertised a telephone line kids could call to speak to Santa.

Accidentally printed one digit off from Sears' Santa line, the number that made it in the paper was instead the top-secret link to Shoup's red phone.

Shoup stationed some airmen on the red phone to field the calls that kept pouring in from children wanting to talk about their Christmas lists.

Then he sorted things out with the phone company, which gave Sears Shoup's old top secret number and set him up with a new one.

A crisis had been averted.

And, though he wouldn't know it then, the seed of a 63-year tradition had been planted.

Like clockwork

The mission starts every year at midnight – like Christmas Eve clockwork.

Once the calendar hits Dec. 24, the North American Aerospace Defense Command (NORAD) checks in with its North Pole Santa Cam.

Based in Colorado Springs, the command watches the skies and seas for any aerospace or maritime approaches, coordinating with other commands to address potential threats to Canada and the United States.

But on Christmas Eve, its technology is also used to track Santa's movements, employing a mess of warning and radar systems and satellites with heat-detecting infrared sensors that hover 23,000 miles above the Earth.

More:Will NORAD's Santa Tracker still monitor St. Nick's journey even if there's a government shutdown?

"On a day-to-day basis, we use those same satellites to monitor missile activity throughout the globe to determine whether they're a threat to Canada and the U.S. or not," explained Capt. Cameron Hillier, who is stationed at NORAD.

"However, on the 24th, these same infrared sensors can also detect the heat from Rudolph's nose."

For 63 years, NORAD – or CONAD, until 1958 – has boasted an impressive Santa Claus tracking system, enlisting hundreds of volunteers to field tens of thousands of calls from children across the globe every Christmas Eve.

And it all started with Shoup in 1955.

After the phone number mix-up, Van Keuren, now 69 and living in Castle Rock, said her parents went to deliver Christmas cookies to CONAD's Operation Center on Dec. 24.

The center – inconspicuously housed in a windowless, cinder block building in downtown Colorado Springs – was home to a three-story clear, Lucite map of North America.

Workers would stand behind the map on scaffolding, updating it with any unidentified flying objects that had been spotted in North American air space.

"And (someone) had drawn this beautiful sleigh coming over Canada," Van Keuren said.

When the airmen and officers saw the colonel, they apologized profusely.

"Do you want us to take it down?" they asked.

"No," he replied.

Instead, Shoup decided to call a local radio station.

"This is Colonel Shoup, the commander of the Command Operation Center in Colorado Springs, Colorado," Van Keuren said in her best impression of her father. "We have an unidentified flying object. Why, it, it looks like a sleigh."

"Well, that of course went all over the world," Van Keuren said.

And it became tradition.

CONAD, and later NORAD, started tracking Santa Claus every Christmas Eve. Over the years, leaders began enlisting volunteers to field calls from children asking about Santa's whereabouts.

The program is now called NORAD Tracks Santa.

Last year, roughly 1,500 program volunteers received more than 126,000 calls throughout the day – an average of 1.8 calls per second, Hillier said.

The program also received 18 million visits to its website and 2,000 emails in 2017. Its latest feature, which started last year and allowed people to ask their Amazon Alexa smart home devices where Santa was, had been accessed 1.5 million times, Hillier added.

Van Keuren has been volunteering to answer phones for the program for the past five years.

"My husband said ... the first call he got last year was from Castle Rock (in Colorado) and the next one was from Stuttgart, Germany," she said. "I swear to goodness, you can't put the phone down without it ringing in your hand."

A legacy

Harry Shoup retired from the Air Force in 1968. He later settled in Colorado Springs, near three of his four children, before his death in 2009. He was 91 years old.

After his CONAD days, Van Keuren admits to giving her father the nickname "the Santa Colonel," a moniker he loved.

"He was a big ol' kid when it came to Christmas," Van Keuren said. "And (he) loved kids, too."

After the Santa Tracker program started accepting emails, someone from the program sent a collection of them to Van Keuren. In them, people wrote to her father, thanking him for picking up the phone that night and starting the tradition.

She printed out the emails for him, and he kept them for the rest of his life, locked inside his prized monogrammed briefcase.

In his later years – after his wife, Louise, died – Van Keuren would take her dad out to lunch.

"And I'd go, 'OK Dad, what looks good ... Dad?'"

"He'd be off wandering around telling people the (Santa Tracker) story," she said.

He did it so often she even got little business cards printed so he could hand them out.

"Col. Harry W. Shoup," they read. "Air Force, retired. The Santa Colonel."

After 28 years in the Air Force, Van Keuren said the Santa Tracker is easily her dad's legacy.

"He really was a good officer," she said, noting that he was even interviewed by Edward R. Murrow for a news program before the Santa mix-up. "But this is what he is known for."

How did he feel about that?

"He loved it. Are you kidding me?" Van Keuren said. "He was as a big a showoff as me."

On Christmas Eve, like they do every year, volunteers with NORAD's Santa Tracker will file into Peterson Air Force Base for their annual duty.

Children will call from China to Germany to Castle Rock, Colorado.

And just like Shoup did when his red phone rang that December day in 1955, someone will pick up.

"Dad did the nice thing. He did the right thing," Van Keuren said. "He could have hung up, but he didn't."

"He did the right thing and look what happened."

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