It was December 1955, the height of the Cold War, when the red phone on Col. Harry Shoup's desk at the Continental Air Defense Command began to ring.
Only an elite few knew the number. Odds were good that a four-star general from the Pentagon was on the other end of the line.
Shoup reached for the phone.
"Yes, sir. This is Col. Shoup," he said.
"Sir? This is Col. Shoup."
"Sir, can you read me all right?"
That's when Shoup heard the little girl's voice.
"Are you really Santa Claus?"
For the last 60 years, officials at the North American Aerospace Defense Command at Peterson Air Force Base in Colorado Springs, Colo., have tracked Santa's whirlwind tour across the globe to deliver presents on Christmas Eve. Nearly 9 million people from more than 200 countries are expected to check in with NORAD's Santa-tracking website before they go to bed on Christmas Eve.
And it all began with that phone call.
As Shoup later recalled in a home video, his first response to the unlikely query was that someone was pulling his leg - and he wasn't amused.
"I said, 'Would you repeat that please?' " he replied.
"Are you really Santa Claus?"
That's when he realized two things: Something had gone wrong with his phone, and the question was genuine.
So he told the little girl on the other end of the line that he was, indeed, Santa Claus. Relieved, she informed him that she would be leaving him food by her fireplace, plus treats for his reindeer as well.
"I said, 'Oh boy, they sure will appreciate that!' "
Then Shoup asked to speak to her mother. That's how he learned that a Sears, Roebuck & Co. advertisement in the local newspaper had invited kids to call Santa at ME 2-6681 - the number for the red phone.
It was a misprint, of course, but that didn't stop kids from flooding the line all the way until Christmas. Shoup assigned a couple of airmen to answer the line and act like Kris Kringle, Shoup's daughter Pamela Farrell recounted to StoryCorps.
After a few weeks, someone at the Continental Air Defense Command (which is now NORAD) had an inspired idea. He went to the giant glass board where airmen tracked the planes in U.S. or Canadian airspace and added a drawing of a sleigh with eight reindeer. They were headed south from the North Pole.
Shoup studied the board. Then he picked up his phone, his other daughter, Terri Van Keuren, told StoryCorps.
"He called a local radio station and said, 'This is the commander of the Combat Alert Center, and we have an unidentified flying object - why, it looks like a sleigh!' "
After that, Van Keuren added, stations would call every hour to ask for the latest on Santa's whereabouts.
The military's Santa-tracking efforts have become considerably more elaborate since 1955.
NORAD's online tracker plays Christmas tunes while flying reindeer pull a red sleigh over images of the Earth provided by NASA. The site shows Santa's last stop and gives an ETA for his next destination. It also keeps a running tab of the number of gifts delivered.
Those who find websites passe can download the NORAD Tracks Santa app from the iTunes store, follow @NoradSanta on Twitter, "like" NORAD's tracker on Facebook or keep tabs through a variety of other social media sites.
More than 70,000 children still call NORAD to talk to Santa on a toll-free line - 877-HI-NORAD or 877-446-6723 - and another 12,000 or so send emails to firstname.lastname@example.org.
All of this would have been impossible for Shoup to imagine as he spoke to the little girl who inadvertently kicked the whole thing off 60 years ago.
Before handing the phone to her mother, the girl asked a question that was certainly appropriate for an Air Force colonel: How is it possible for Santa to visit so many houses in a single night?