They knew all about BVR, just had to use relays - and had a crypto system…. *
Then they had a hybrid system once the electric telegraph system was invented. **
Then, of course, there was the RN Pigeon Service…
* https://www.waterlooassociation.org....moveable-arms/
Balls and Flags, Shutters and Moveable Arms
** https://www.usni.org/magazines/proce...-coast-signals
Naval Coast Signals - 1889