In UK there used to be two lines into each s
V-bomber station and dispersal. Every so often, it could have been as often as 15-30 seconds the bomber box would bleep. I don't know how many lines there were out of Bomber Command. Occasionally we would get a fail light on one line or the other. From the fault reports we knew one ran up west of UK.
Later the lines into the station were doubled to four so we rarely lost comma, if at all. On one occasion, in an exercise, Machrihanish reported loss of comms. We were just approaching the Scramble. I opened two Flash calls, one on the military circuits and a military Flash on the public service. The GPO beat the military connection by a good few seconds.
We also had direct sub-trunk lines too.
In SAC HQ, when the controller initiated a broadcast receiving units would respond through a light acknowledgment. I don't recall our stations acknowledging readiness calls but at my level we were usually too busy, the assistant may have done so.