We used field phones all the time when I was in light infantry (82nd Airborne). Pretty much any time we were in a fixed position out would come the commo wire so as to not give our position away.

They even went as far as having us string wire out to our ambush sites when we were on the Iraqi border during the first gulf war and reel it back up when we came in. Zero radio signals out there because they didn’t want them to know that a whole division plus French armor was there.

Modern tech is good and all unless you have some dumb Joe that keeps erasing the codes out of the radio by turning on the truck without putting it on standby or something…never quite figured that one out.