S42.3 FuMB 1 “Metox R600A.” German Warning Receiver l=0.60- 2.60m To protect submarines from surprise attacks by AVC airplanes, they get the receiver “Metox R500A” (S40.3) or “Sadir R97E” (S40.5) that sounds a warning when search pulses hit it. Because time is short, the receiver is operated with the antenna “Honduras” (S42.4.2). It is later replaced by the solidly mounted “Bali” antenna (S42.4.3) At the same time a visual display is introduced to replace the nerve-wracking warning sound. S42.4.0 German Ship Antennas for the Range of 1.50m S42.4.1 FuMB Ant 1 “Hondo” “Hondo” is a simple array antenna used by torpedo speed boats. It has an eight-shaped characteristic and must be rotated constantly. S42.4.2 FuMB Ant 2 “Honduras” (“Biskayakreuz”) The “Honduras” antenna planned for submarines consists of two horizontal arrays of different lengths flexed downward that are hand held and taken into the submarine before submersion. Because of its eight-shaped characteristic it also must be rotated constantly. S42.4.3 FuMB Ant 3 “Bali” (“Häschen”) Round Antenna The solidly mounted, sea-worthy “Bali” antenna consists of a broadband, horizontally polarized array that has two additional vertical rods to receive the vertically polarized waves, thus the name “Häschen” (“Bunny”). The “Bali” antenna has a circular radiation and a range of l=0.75-3.00m
FuG 350 Naxos I FuG 350a Naxos Ia
Centimetric ASV radar was first used (in an experimental installation) against submarines on 17 March 1943. Metox did not detect these wavelengths, so that surprise attacks on U-boats were once again possible. Within a few weeks aircraft equipped with ASV Mk.III radar made the Bay of Biscay very unsafe for U-boats. By May 1943, Dönitz was aware of the seriousness of the situation, although he still believed that it was caused by emissions of the Metox receivers. Actually, clear evidence had been presented to the Germans when a Stirling bomber carrying a 10cm H2S radar crashed near Rotterdam, in the Netherlands, on 2 February; but apparently this information was slow to reach the Kriegsmarine.
All excellent shot of the Naxos detector. Seen here on U-952 under command of Kapitänleutnant Oscar Curio.
The Naxos radar warning receiver was built by Telefunken, using components of the FuG 25 Zwilling IFF equipment. It operated between 2500MHz and 3750MHz (wavelengths of 12cm to 8cm), with a detecting range against H2S and its ASV derivatives of about 8km, thanks to a sensitive detector and a multi-stage amplifier. Actually it was too sensitive and caused unneccessary dives by U-Boote. The first Naxos receiver was tested in an aircraft on 11 September 1943. Development had been delayed by an air attack on the Telefunken works.
The original Naxos I had a vertically polarized antenna, with poor results as the British radars initially used horizontal polarisation. (This seems to have been a case of the German designers being smarter than the British ones, with unfortunate consequences.) Naxos Ia had a triple antenna, with elements crossing each other at 45 degrees to avoid this problem. Over 1000 sets of Naxos I were produced, for U-Boot installations but also for the Luftwaffe, the original customer.
(Later versions of Naxos could indicate the approximate direction of enemy aircraft carrying the radar. But this was useful primarily for aircraft, and probably was not installed in submarines?)
The first Naxos equipment was ready in September 1943. In November 1943, the British became aware that U-Boot contacts were lost as the attacker approached, presumably because it detected the 10cm ASV radar. In reaction, ASV Mk.VI had an attenuator, so that the aircraft could limit the power it radiated and give the false impression that it was not approaching.
Also in late 1943 the development of the 3cm ASV Mk.VII radar was commissioned, in anticipation of the appearance of 'Naxos'. This was a development of versions of H2S radar that operated on 3cm. At the end of the war a 3cm version for the Luftwaffe of Naxos was ready, but only about 100 were constructed. If the war had continued, they could, and probably would, have been fitted to new submarines.