While it is true that many U-Boats kept a old few devices installed, it's extremely likely that they'd have dropped the FuMB 1 'Metox' like a proverbial hot rock as soon as they could do, since it actually increased the chance of being detected as allied radar improved...
Check out this German report from 1943:
'Gruppe West reports, as a result of experiments., that the Metox radar interceptor produces radiation of its own, which can be detected at the following distances... 23km at 500m altitude, 33km at 1000m altitude and 50km at an altitude of 2000m.'
Incidentally this was way beyond the 'Metox' useful detection range, effectively making it a liability in many cases, rather than an aid - which is sort of fitting, since it was made by a French company!
Also check out this official order to all German subs sent in summer 1943:
'Use of the Metox and Grandin RWRs is now forbidden in all sea areas.'
With that in mind, the deletion of older RWR devices in GWX is broadly accurate.
In actual fact this emission problem was not the only issue with the early German radar detectors, which emitted an audio warning as well as a visual indication on an oscilliscope. It was often not realised that the audio signal was generated from the pulse repetition frequency of the detecting aircraft search radar. At high PRF it was quite possible for the RWR to generate a warning audio signal which was actually outside the range of human hearing, so if nobody was watching the oscilliscope, thinking they'd get an audio warning too, they'd be in for a shock!
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