WILLIAM BRANGHAM: During the Cold War, Air Force Colonel Harry Shoup was one of the commanders in charge of an early warning radar system based in Colorado.

It had been set up to detect a possible Soviet missile attack on the U.S.

In this animated conversation from our colleagues at StoryCorps, three of Shoup's children recall a surprising phone call their dad received back in 1955.

WOMAN: I remember two phones on his desk.

One was this red phone.

Only a four-star general at the Pentagon and my dad had the number.

MAN: This was the '50s.

This was the Cold War.

And he would have been the first one to know if there was an attack on the United States.

WOMAN: So, first couple weeks of December, in 1955, dad was at the office and the red phone rang.

He answered it, "This is Colonel Shoup."

And then there was a small voice that just asked: "Is this Santa Claus?"

MAN: Dad was very straitlaced, very disciplined.

WOMAN: He was annoyed.

WOMAN: He was upset.

(CROSSTALK) MAN: He thought it was a joke.

WOMAN: Yes, and so now the little voice was crying.

WOMAN: And dad realized that it wasn't a joke.

So he'd talk to him: "Ho, ho, ho," and asked if he had been a good boy, and "May I talk to your mother?"

And the mother got on and said: "You haven't seen the paper yet?

There's a phone number to call Santa.

It's in the Sears ad."

Dad looked it up and there it was, his red phone number.

And they had children calling one after another.

So he put a couple of airmen on the phones to act like Santa Claus.

WOMAN: It got to be a big joke at the command center.

The old man's really flipped his lead this time.

We're answering Santa calls.

WOMAN: The airmen had this big glass board with the United States on it and Canada.

And when airplanes would come in, they would track them.

MAN: And Christmas Eve of 1955, when dad walked in, there was a drawing of a sleigh with eight reindeer coming over the North Pole.

WOMAN: Dad said: "What is that?"

They said: "Colonel, we're sorry.

We were just making a joke.

Do you want us to take that down?"

Dad looked at it for a while.

And next thing, dad had called the radio station and had said: "This is the commander at the Combat Alert Center, and we have an unidentified flying object.

Why, it looks like a sleigh."

(LAUGHTER) WOMAN: Well, the radio stations would call him like every hour and say, where's Santa now?

And later in life, he got letters from all over the world, people saying, "Thank you, Colonel, for having this sense of humor."

And in his 90s, he would carry those letters around with him in a briefcase that had a lock on it, like it was top secret information.

He was an important guy.

But this is the thing he's known for.

MAN: It was probably the thing he was proudest of.

WOMAN: Oh, I'm sure, yes.