Tricking German Submarines

The Germans knew the frequency we were working on. So they put a radio set in their submarines, and they converted this to audio sound. And to do that, they had to have an oscillator on the submarine. What they hadn’t thought of, was the fact that oscillators transmit. So we could pick up their oscillator in the aircraft. We put a detenuator on the transmitter so that our signal, instead of getting stronger, was getting weaker to them. They thought we were going away. We had lights on the underside of the aircraft. Suddenly you turn it on, it’s like daylight and they’re caught off above water. They had tricks on us too.