From Scott Gray, KD4VVC:
Circa 1943. “Office of Strategic Services. Field Photographic Branch… Click here to view Instructional Film: Describes the radio transmitter-receiver unit used during World War II. Explains compactness and ease of concealment, and outlines operations in detail: selection of electrical outlet, battery, or combination of both as power unit; antenna, assembly parts, installation, frequency determination and receiver operation; parts installation, attachment of crystal equipment and transmitter operation.”