German WWII Elint

[USS ALASKA]

Hello gentleman – first post here. Looking for some info on German warship electronics and this looked like the place to ask. Been reading ‘If The Gods Are Good – The Epic Sacrifice Of HMS Jervis Bay’ by Gerald L. Duskin and Ralph Segman. In the beginning of the book – setting the stage for the Jervis Bay / Scheer battle, the authors write about Scheer hunting convoys. The authors write that “Under way, the convoy ships maintained their positions in the array and observed radio silence, though some receivers leaked detectable oscillations.” and “Krancke was concerned that he would miss the convoys. He consulted his electronics and decoding officers, but they reported no trace of convoy radio oscillations.” What I believe the authors are referring to here is trying to detect BFO radiation, (Sorry - Beat Frequency Oscillator, not Blinding Flash of the Obvious.) Is this correct? In ‘Spycatcher’, Peter Wright gives a good explanation on how this is done and how it can be used. Anyway, BFO is a very low level power output. Granted, there is no terrain masking – man made or otherwise – on the open ocean and salt water is great for RF propagation but it would seem to me that you would be almost up on top of the target before you would detect it’s BFO. Does anyone know if the Germans used any special equipment for detection of BFO RF or just the standard onboard receivers and antennas? Did they try to DF these signals or just use this procedure to alert them to someone being in the area?

Thanks for your help. Lots of good info here.

[tommy303]

Are you referring to emitted radiation from superheterodyne receivers? Radios using superheterodynes often do leak onto the antenna and can be detected at relatively close ranges. You would not necessarily need special equipment, though a purpose built detector would help you scan for an emissions source along a particular frequency in a place where there should not be one The Japanese were quite successful in tracking US units using 455kHz transmitters, so it is certainly possible. However, the amount of energy being leaked by a receiver is very small and detection ranges are correspondingly short.

[USS ALASKA]

Sir, as far as I can tell, that is what the authors are referring to. The quotes are all they state about it. If that is the case, I wouldn’t have thought that method would have provided much help in hunting merchants unless you can DF it. And with the low power we are talking about, I was just wondering how much use this technique really is. Of course, if you don’t or can’t launch a plane and don’t wish to turn on your radar for fear of detection, and vis is low for whatever reason (weather / darkness) any info on adversary placement is helpful. And if the radio operators aren’t doing anything else, why not have them watch for those emissions.

Could you elaborate on the Japanese use of this procedure? This is the first I’ve heard of it. Thanks for the help.

[tommy303]

I am a little sketchy on the details, but as far as I know the Japanese set up listening posts to try and detect leakage originating from US superheterodyne transmitters set to 455 kHz. This was largely on land so far as I know and they were using that to zero in on US recon patrols. Eventually the US Army realized what was happening and there own transmitters were giving their patrols away, even when the recon teams were not transmitting. Steps were taken to redesign and better shield the transmitters so that leakage no longer occurred.

I have heard that in Europe, some captured British flight personnel gave the Germans false information in 1940 or 41 that the British were able to home in on German transmitters, both radar and radio, by detecting the weak signals produced by transmitters which though switched on, were not in active use. This led the Germans to unnecessarily explore ways, and waste a good deal of time and resources, of trying to detect similar British signals and shielding or redesigning their own equipment.

[Dave Saxton]

The idea that the Allies were using the Metox's local osscilater to locate U-boats was a clever lie by a British POW. The Germans were trying to figure out why U-boat losses started to go through the roof in the spring of 1943. The cause was the introduction of centimetric radars, and of course the Metox was useless for detecting those wave lengths. To protect the secret of ASV MKIII (H2X), the British POW made up the storey. To those in the U-boat arm that were at their wits ends, and who were not privy to Rotterdam, briefly latched on to this idea, although the Allies had no such capability.

Those knowlegable in radar quickly understood what was really going on, but they were not at liberty to consult the u-boat commands, because of severe secrecy rules. Doenitz forbad further use of the Metox, and also a bit later the Wanze, although Doenitz as Grand Admiral was probably aware of Rotterdam. Most Allied ASW radar was still metric so these prohibitions actually made things worse. I'm not sure that Doenitz ever fully understood the more technical and scientific aspects of radar, however. Eventually the KM developed a full understanding as the NVK, industry, and other technical people were able to advise the naval commands. They also got further comfirmation from an unexpected source.

After the British POW had planted the false idea, an American POW was captured. The American POW was highly trained in all aspects of radar and he spilled the beans competely:

"An American, almost certainly from the AAF ASW service, with a radar specialty and considerable experience, did not just answer questions, he gave a short course in microwave radar and it's use against U-boats that fills 11 pages of report. He explained the operation of both 10 and 3cm equipment, he described the underwater microphones (sonobuoys) that transmitted the sound picked up to aircraft in the vicinity through small radios; he gave the sensitivities for various targets at different ranges; he explained the tactics for attacking a submarine; ...."(L Brown)

[Dave Saxton]

Sir, as far as I can tell, that is what the authors are referring to. The quotes are all they state about it. If that is the case, I wouldn’t have thought that method would have provided much help in hunting merchants unless you can DF it. And with the low power we are talking about, I was just wondering how much use this technique really is. Of course, if you don’t or can’t launch a plane and don’t wish to turn on your radar for fear of detection, and vis is low for whatever reason (weather / darkness) any info on adversary placement is helpful. And if the radio operators aren’t doing anything else, why not have them watch for those emissions.

Could you elaborate on the Japanese use of this procedure? This is the first I’ve heard of it. Thanks for the help.

The German surface ships were equipped with several radar detection devices during the war. Of couse these detected the regular transmissions, not the emissions from the LO of recievers. Some of these detection devices could DF the source of intercepted radar or radio transmissions to a rather fine degree of accuracy. The Timor antenna could DF radio/radar emissions, but we don't usually find it as standard equipement before mid 1941. The use of DF long range radio band monitoring systems had been used from land stations for many years by the Kriegsmarine. These equipment did not require a triangulation fix. The late war Tunis detector (Naxos-T) could DF 10cm band and 3cm band radar transmissions.

[USS ALASKA]

Sirs, thank you for your responses. Interesting stuff. It does generate some more questions however.

10.7 MHz is also another widely used IF frequency. Was any attempt made to detect it or wasn’t it common till after WW II in electronic devices?

Comment to the Japanese collection on US patrols – does anyone know the range they were able to detect these signals? Granted, terrain, weather, other factors all influence that number but just wondering what an average was. With the low power levels we are talking about, I would have thought you would hear a patrol crashing around before you would detect them via this method. But – won’t be the first time I wrong about something.

How do you use a receiver to hunt for 455 kHz if your own set has an IF freq of 455 kHz? Won’t you just be receiving your own signal leakage? Really good filters and shielded system or use a non-heterodyned receiver tuned just for this freq?

The story about the British POW is very interesting. Question about that. Was his story an officially approved cover story? “Hey guys, if you get captured, here is what we want you to say.” Or is it something he came up with on his own? Reason I ask is that if you are the Germans and take the “…were able to home in on German transmitters, both radar and radio…” to an extreme, one would think that you would order your crews to cease all use of said equipment except for emergencies. And wasn’t much valuable intel gathered because of how much they used that equipment? When I read that, the first thing I thought of was that statement could have had some very detrimental side effects – more harmful than the protection of the truth the lie was to cover. Good on him for the effort though – quick thinking.

Once again, thanks for the info and responses. Interesting discussion.

[Bgile]

My job on submarines in the 70s was in this field. We had some pretty sensitive equipment and we looked at pretty much the entire spectrum, but I don't recall local oscillators being a target. It's possible that isolation was much better by then.

[Dave Saxton]

Looking into this local osscilator bussiness, the more things don't add up. They Germans were well aware of the Allied centimetric radar, even the 3cm stuff, by spring 1943. By May they had logged detections of several centimetic radars even at sea and by ASW aircraft. Why would they continue to chase their tails with the local osscilator theory when they already know this? Secrecy was of course severe and most in the KM would not know this. However, we seem to have Doenitz not knowing which end is up. Nonetheless, he's the Grand Admiral and privy to Rotterdam, and then we have Doenitz banning the use of the Metox, but allowing the use of the Wanze. Naxos becomes available but we have him instructing the skippers to use the Wanze and Wanze II (with less LO emission) along with Naxos.

Next we have Dr Runge of Telefunken R&D, and also actually on the AGR, a designer of Naxos, seeminly chasing his tail by studying the LO problem and confirming the British POW's story. What?

I think the Germans new the LO giving away their poisition was nonsense, but they continued the charade to mis -lead Allied intelligence, just in case the Allies actually put any stock in it, and because it made a nice cover for Rotterdam and the development of effective counter measures to the Allied centimetric radars. KM personal would continue to fall into Allied hands, just as Allied personal would fall into German hands. The Germans also new they had a mole(s) somewhere in their radar community.

These kind of games are played out all the time. For example, the British continued to run a program of agents in Norway, even though Ultra provided all the information they needed. However, the agents gave the Germans an obvious place to look for the leaks, protecting Ultra.