Hi Simon, it was true that Metox emissions acting as a homing device for aircraft to zero in on uboats. As an aside, RAF Bomber Command had a radar warning reciever called "Monica" that did exactly the same thing, allowing German nightfighters to home in on it's emissions. Radar was new technology during WWII, and alot was not understood about it's capabilities and vunerabilities. The allies did a much better job unraveling radar's mysteries then the Germans during the war and were thus able to get alot more effective use from radar.
Ernest