Ya got me man.
Why do they call that thing the little woman does to her hair once a month/(2) that costs 100+ bucks a "permanent"?
I'd guess because it connects to the intercom system (without a separate wire to each guy).
Things were revolutionary/primitive back then.
My Uncle said they just kicked the driver in the left shoulder when they wanted him to turn left, because you couldn't hear the voices in the intercom above the engine/gunfire/airplanes, other battlefield noises.

__________________

Morbius, Morbius! Something is approaching from the Southwest. It is now quite close.