Col. Harry Shoup was a real by-the-book guy.

At home, his two daughters were limited to phone calls of no more than three minutes (monitored by an egg timer) and were automatically grounded if they missed curfew by even a minute. At work, during his 28-year Air Force career, the decorated fighter pilot was known as a no-nonsense commander and a stickler for rules.

Which makes what happened that day in 1955 even more of a Christmas miracle.

It was a December day in Colorado Springs when the phone rang on Shoup's desk. Not the black phone, the red phone.

"When that phone rang, it was a big deal," said Shoup's daughter Terri Van Keuren, 69, a retiree in Castle Rock, Colorado. "It was the middle of the Cold War and that phone meant bad news."

Shoup was a commander of the Continental Air Defense Command, CONAD, the early iteration of the North American Aerospace Defense Command (NORAD). Then, as now, the joint U.S.-Canadian operation was the tense nerve center of America's defensive shield against a sneak air attack. In 1955, the command center was filled with a massive map of North America on plexiglass, behind which backward-writing technicians on scaffolds marked every suspect radar blip in grease pencil.

It was not a place of fun and games. And when that red phone rang - it was wired directly to a four-star general at the Pentagon - things got real. All eyes would have been on Shoup when he answered.

"Col. Shoup," he barked. But there was silence.

Until, finally, a small voice said, "Is this Santa Claus?"

Shoup, by all accounts, was briefly confused and then fully annoyed. "Is this a joke?" Glaring at the wide-eyed staff for any sign of a smile, he let the caller have it with all the indignity of a bird-colonel who brooked no nonsense on this most vital of all phone lines.

"Just what do you think you're doing," he began.

But then the techno-military might of the United States was brought up short by the sound of sniffles. Whoever was on the phone was crying, and Shoup suddenly realized it really was a child who was trying to reach Santa Claus.

The colonel paused, considered and then responded:

"Ho, ho, ho!" he said as his crew looked on astonished. "Of course this is Santa Claus. Have you been a good boy?"

He talked to the local youngster for several minutes, hearing his wishes for toys and treats and assuring him he would be there on Christmas Eve. Then the boy asked Santa to bring something nice for his mommy.

"I will, I will," Santa-Shoup said. "In fact, could I speak to your mommy now?"

The boy put his mother on the phone, and Shoup went back to business, crisply explaining to the woman just what facility their call had reached.

"He said later he thought she must have been a military wife," said Van Keuren. "She was properly cowed."

But she also had an explanation. The woman asked Shoup to look at that day's local newspaper. Specifically, at a Sears ad emblazoned with a big picture of Santa that invited kids to "Call me on my private phone, and I will talk to you personally any time day or night."

The number provided, ME 2-6681, went right to one of the most secure phones in the country.

"They were off by one digit," Van Keuren said. "It was a typo."

When Shoup hung up, the phone rang again. He ordered his staff to answer each Santa call while he got on the (black) phone with AT&T to set up a new link to Washington. Let Sears have the old number, he told them.

That might have been the end of it. But a few nights later, Shoup, as was his tradition, took his family to have Christmas Eve dinner with his on-duty troops. When they walked into the control center, he spotted a little image of a sleigh pulled by eight unregistered reindeer, coming over the top of the world.

Van Keuren was only 6 at the time, but the exchange that followed became stuff of both family and Air Force legend.

"What's that?" the commanding officer asked.

"Just having a little fun, Colonel," they answered, waiting for the blowup.

Shoup pondered the offense as the team waited. Then he ordered someone to get the community relations officer. And soon Shoup was on the phone to a local radio station: CONAD had picked up unidentified incoming, possible North Pole origin, distinctly sleigh-shaped.

The radio station ate it up, the networks got involved and an enduring tradition was born. This Christmas Eve will mark the 63rd straight year that NORAD will publicly track Santa's sleigh on its global rounds.

"This is our most feel-good mission," said Maj. Andrew Hennessy, a Canadian Army officer posted at NORAD headquarters in Colorado. "We know Santa brings lasting joy to kids around the world and we're glad to have that as our fourth mission one day out of the year." (On the other 364 days, NORAD's three-pronged mandate is to oversee air threats, general aerospace control and, in recent years, maritime warnings for potential threats from sea.)

In good military fashion, the Santa tracking command has grown terrifically complex. NORAD deploys satellites, radar, jet fighters and Santa cams to feed its website, apps and social media accounts used by more than 2 million followers. Naughty and nice alike can follow Santa's movement on 3-D maps in eight languages. Last year, when Alexa was asked "Where's Santa?" more than 1.5 million times, it was NORAD that fed her the answer.

But the real emotional outlay comes in the Colorado Springs live call center, staffed for 20 hours on Dec. 24 by more than 1,500 volunteers (many of them local service members and their families). With a nine-page Santa Tracker manual in hand, they fielded more than 126,000 calls in 2017.

"As soon as you put the phone down, it rings again," said Hennessy, who has done duty in the call center. He remembers telling one young Boston caller that Santa had been confirmed over Maine heading south but - and this is a primary NORAD message - the sleigh wouldn't stop unless the boy was in bed.

"The next thing I heard was the phone hitting the floor," he said. "Mom picked it up and said, 'Can I call you back, he's never done that before.' "

Shoup went on to ever-higher ranks in the Air Force, retiring as a wing commander. When his kids were old enough, he told them why so many of his colleagues called him the "Santa colonel," but it was a quiet kind of legacy until the 25th anniversary of Santa tracking and TV news crews sought him out.

After that, he looked forward to getting the media calls each December, even carrying special business cards with the story typed on the back. In 2009, Shoup was buried, at 91, with a flyover of F-16 fighters, under a gravestone that notes his service in World War II, Korea and Vietnam. The last line reads: "Santa Colonel."

"I want his message to be 'Do the nice thing,' " said Van Keuren. "A lot of people would have hung up on that kid."

This story first appeared in The Washington Post