In a few years - the early 1950s - the IFF sets were SIF encoded, where each aircraft or ship, when interrogated by a radar, would reply with an octal pulse code 0000 to 3777. The interrogating radar would then read the pulses, compare them to the code of the day, and modify the video to the scopes automatically (AN/UPX-1, AN/APX-25, AN/UPA-24, for those paying attention) to the operator could call the shots. I think there are remnants of this ancient system still in use.