Seventy-five years ago this month, the December 1943 issue of Radio Craft included a description of this light-phone reportedly in use by the Germans.

The set could operate in three modes: white light, red light, or infrared. Obviously, simple morse signalling was possible, but the beam could be modulated with audio.

The article noted that the applications of the device were rather limited, but wondered whether the Allies would be adopting a similar system at some point.