The value of the Kristalldrehbasisgerät (KDB) over the Gruppenhörchgerät (GHG) is that the KDB does not have a deaf-zone at the front. The GHG (the basic type of hydrophone) was basically a set of microphones build into outer-hull of the boat. It had little to no sensitivity to the front and rear( which also has the prop and engine noise there). The KDB just had the conningtower obstructing the sounds and ofcourse the engine and prop-noises to deal with. But it had free 'view' to the front. And was easier and more accurately to direct it's sensitivity compared to the electronic way of directing sensitivity with the GHG. Is it worth the renown? I don't know. The crew doesn't drop the signal as much as it did with the GHG.
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