During World War II, Germany developed a hand-crank 500 kHz rescue radio, the "Notsender" (emergency transmitter) NS2. It used two vacuum tubes and was crystal-controlled. The radio case curved inward in the middle so that a user seated in an inflatable life boat could hold it stationary, between the thighs, while the generator handle was turned. The distress signal, in Morse code, was produced automatically as the crank handle was turned.
An NS2 unit was captured by the British in 1941, who produced a copy, the Dinghy Transmitter T-1333. Britain gave a second captured unit to the United States, which produced its own copy, the SCR-578. United States Army Air Forces aircraft carried the SCR-578 on over-water operations.
Named the Gibson Girl
because of its hourglass shape, it was supplied with a fold-up metal frame box kite, and a balloon with a small hydrogen generator, for which the flying line was the aerial wire. Power was provided by a hand cranked generator. The transmitter component was the BC-778. The frequency was 500 kHz at 4.8 watts, giving it a range of 200 miles (300 km; 200 nmi). Keying could be automatic SOS, or manual. Crystals were a scarce item for the U.S. during the war and the SCR-578 was not crystal-controlled.