This huffduff story is ridiculously plausible. It is so plausible that if Waterhouse were working for the Germans, he’d be suspicious. The antenna is a highly directional model. It receives a strong signal when pointed towards the source and a weak signal otherwise. The operator waits for a U-boat to begin transmitting and then swings the antenna back and forth until it gives the maximum reading; the direction of the antenna then gives the azimuth to the source. Two or more such readings, supplied by different huffduff stations, can be used to triangulate the origin of the signal.