It began 70 years ago when a five-year-old called a top-secret emergency line reserved for the U.S. president and four-star generals and asked, “Hello, is this Santa?”

It was December 1955 — the height of the Cold War. The phone that rang was big and red, only to be used during an international emergency.

That wrong number — and many others that followed because of a simple typo in a newspaper ad — ended up launching a mission like none other for the North American Aerospace Defense Command, NORAD: to develop a tracking system allowing families to follow Santa’s journey around the world.

Since then, the Santa Tracker has become a source of joy for millions of children.