Lee Enfield SMLE Morse Code Signal Shutter Panel, Seen on eBayUK

[Surpmil]

Gives some useful perspective on pigeons doesn't it? And the other good thing about them was their roosts could be at whichever chateau or distant battery C.P. the message was intended for; avoiding all the usual problems of passing messages along through different levels in a formation. In fact when one thinks about the security problems of electronic warfare today, the homing pigeon may not have seen the end of war!

Lamps were handicapped by the low intensity bulbs of those days I suppose, not to mention their fragility and the difficulty of the receiver locating them in mist, smoke or blast. The need to stick one's head over the parapet or peer about with a periscope can't have helped either, nor the need for both parties to know Morse code. Though of course in those days Boy Scouts learned it in their tens of thousands.

Runners and wires...