P,
There was another contentious line between the caboose and the head end and I'm not talking about the Signal Line on Passenger Cars.
They used the brake line to communicate back and forth. The conductor could let a small amount air out of the brake line to communicate the everyone was on the caboose by closing the valve or send a Highball by doing 2 very small releases that could be seen on the head ends air gauge. It was also used besides the whistle for helper communication.
As kinda a Train Order operator (not professionally), I view the operator as the, eyes, ears, and hands of the Dispatcher, as we have to write out the Train Order he dictates to us (then we have to read it back that we got it correct), and we have to set the Train Order Signal as he directs, and also OS (report) trains as the go by, it was the same for tower operators and CTC control operators.
Radios were not all that necessary. As the used a lot of hand signals.
A good site to look at is:
[
wx4.org]
TT&TO fringe lunatic,
Ray Eiser