Naxos radar detector
Two versions were widely used, the FuG 350 Naxos Z that allowed night fighters to home in on H2S radars carried by RAF Bomber Command aircraft, and the FuMB 7 Naxos U for U-boats, offering early warning of the approach of RAF Coastal Command patrol aircraft equipped with ASV Mark III radar.
A later model, Naxos ZR, provided warning of the approach of RAF night fighters equipped with AI Mk.
Unlike other types of tube electronics of the era, which are quite fragile, the main component of the magnetron is a large block of copper.
If an aircraft carrying one were shot down and recovered, there was a very good chance the block would survive, at which point the secret would be revealed to anyone familiar with microwave techniques.
This is precisely what occurred on the night of 2/3 February 1943, when the second mission to attempt to use H2S led to one of the Short Stirling bombers carrying it being shot down near Rotterdam.
The magnetron was recovered and this Rotterdam Gerät (gadget, or device) led to the rapid formation of a study group to exploit it.
This effect was hampered by the industry's recent decision to give up on microwave research, considering it to be a dead-end, as had British engineers before the introduction of the magnetron.
Adding to their problems was the lack of a suitable rugged crystal detector, which was the only system able to reliably detect these high frequency signals.
Operators found it useful for finding the bomber stream, at ranges as great as 35 kilometres (22 mi), but could not use it to home in on individual aircraft.
The Naxos Z system's rotating antenna for airborne use was driven by a DC motor, and comprised what appear to be a pair of vacuum tubes laid flat on a circular rotating carriage,[1] which would be enclosed within a radome of either hemispherical shape for single-engine fighter use, or in a more aerodynamic "teardrop" shape for placement atop a twin-engined night fighter's canopy.
News of the device made its way to England, where some level of panic broke out when it was suggested that the H2S could be leading to the aircraft's demise.
Aircraft that did survive reported that there was no warning of the attack, and it was quickly surmised that the RAF had introduced a new microwave AI radar.
A new phase started where British aircraft pressed into the Bay of Biscay and German submarines were told to remain on the surface and fight it out in daylight rather than risk almost certain death at night.
III, by 1944 the British and US were already well on their way to introducing newer magnetron-based radar systems, like the American H2X, operating at even higher frequencies in the 3 cm band.
