ARC-5 is a series of radio equipment that was used heavily in aircraft in WWII. They are also called "command sets". A large amount of this equipment was manufactured, and many were available on the surplus market after the war. As a teen, my first transmitter was an ARC-5 that covered 80 meters.
Here are two transmitters and a transmitter rack.
It was modified by a ham, I assume that this is a simple AM grid modulator built into the rack.
Back to NS1W ham radio page...