Identification friend or foe

Back in the mid-50s, 54 through 58, when we put up our first satellites, there were actually transmissions from UFOs to our air defense radar stations, to our electronic warfare aircraft, and the UFOs literally used our codes to are coded transmissions to identify themselves as friendly.

What were those? It's called IFF, identification friend or foe.

And basically the way it works is you send a very specific radar frequency out to the aircraft.

The aircraft has a receiver tuned to that frequency and it has a code book.