No, this device wouldn’t pick up music from the United States Marine Corps, but it would allow your car radio to listen in on the local maritime radio traffic on the 2-3 MHz marine band.

The project appeared in the April 1961 issue of Electronics Illustrated. It used a single 2N140 transistor as an oscillator on 3.5 MHz, when mixed with the 2-3 MHz signals, the output could be heard on the broadcast band. It was powered by a battery which was said to be good for hundreds of hours with the low current drain circuit.

The cost was said to be about $10, which would quickly be paid back with fresh fish. The idea was that by monitoring the traffic from commercial fisherman, the hot fishing spots would be revealed.