Each year, millions of children follow Santa’s journey around the world with the NORAD Santa Tracker, which uses military radar to track Santa’s flight as he delivers presents to all the good little boys and girls. But not everyone knows that this beloved Christmas tradition began over 50 years ago with a typo in a newspaper ad in Colorado.

In 1955, Sears Roebuck & Co. placed an ad in a Colorado Springs-area newspaper with a phone number that children could call to speak with Santa Claus. But the misprinted number was not a direct connection to the North Pole, but rather a connection to a telephone on the desk of the Continental Air Defense Command’s chief of operations, Colonel Harry Shoup.

Terri Van Keuren, one of Shoup’s daughters, remembers the red phone being an important issue.

“Only a four-star general in the Pentagon and my father had the number,” Van Keuren told StoryCorps when she and her siblings visited recently to tell the story of how the Santa tracking program began.

When the phone rang one day in December, Colonel Shoup was surprised to hear a quiet voice on the other line asking for Santa Claus. Although Shoup was initially upset about the call, he played along, his children telling StoryCorps. As the calls continued, Shoup began manning the line with airmen assigned to Santa Claus. On Christmas Eve, airmen attached Santa’s sleigh to the glass panel in the command center used to track flights over the United States.

“Next thing you know, dad called the radio station and said, ‘This is the commander of the Combat Alert Center and we have an unidentified flying object. It looks like a sleigh.’ Well, the radio stations would call him like every hour and say, ‘Where is Santa Claus now?'” Van Keuren said.

And so a tradition was born.

Shoup’s children say he received letters from around the world thanking him for having a sense of humor and starting a tradition beloved by so many.

The North American Aerospace Defense Command (NORAD) assumed responsibility for tracking Santa Claus in 1958. To this day, NORAD employees, as well as family and friends, volunteer their time to respond to children’s calls, letters and emails and to track Santa’s flight every Christmas.