[RodM]

For SES, extracts from Air Ministry Report:


Air Scientific Intelligence - Report No. 83 - Recent Developments in German Route Tracking and RCM (dated 26.3.45)

Since report No. 73 (July 1944) new developments highlighted -

1. formation of specialist RCM unit
2. spread of route tracking to GCI stations
3. use of listening recivers for guiding long-range radars

It notes that the function of the RCM unit is largely deployed in the problem of jamming Oboe.

1. RCM Development - History

Nov 1943, special detachment of German Air Signals Experimental Regiment established near Duisburg for investigating methods of defence against Oboe. The unit was able to cover most Oboe transmissions in Germany from Duisburg.

During 1944, transmissions were plotted successfully by listening and Oboe Mk I was then successfully jammed. In May 1944 the unit was commended for it's work during a big attack on Duisburg.

The unit had managed to identify and plot Oboe Mk II transmissions and thusidentify the main raids from the spoofs - being the only unit which gave a clear picture of the Duisburg raid.

The techniques developed were then passed on to the whole route tracking organisation.

In the second half of 1944, a jammer against centimetic Oboe was introduced. The unit is began to develop counter-measures against other navigational aids.

2. Deployment

Very little info known (since the intelligence service had difficulty tracking movements via ULTRA because of a change in unit nomenclature by the Germans). Unit concerned was IVth Abteiltung of LN Regiment 351 with 25 to 30 stations in Western Germany. Most stations were deployed in the valley of the Rhine. With Allied advances, units were forced to withdraw and deployment (at date of report) not known. Units were mobile and it was assumed that because of fuel shortage, mobile generators were not an option so they would have to be positioned close to a electricity supply.

3. Listening

New procedure developed where unit claimed to be able to give "10-15 minutes" warning of target.

It turned out that new method was simply listening to W/T traffic between Oboe ground stations (presumedly on the continent), so Oboe procedure was tightened up and land lines used for communications more often.

4. Jamming

Method of jamming Oboe Mk I was relatively simple to achieve. Modified Freya used to interrogate the a/c set, wait unit the the a/c was close to the release point and then jam the signal.

Equipment used to jam centimetic Oboe was device called "Ali-Baba Gerat" - at least three versions produced to cover metric and centimetic Oboe. This device seen as centimetic jammer employing two methods to jam -

(1) straight interrogation
(2) Method known as "Ball" - Korfu D/F sets are used to try to lock in on the signal (cm Oboe transmissions narrower and more directional making it hard to stay focused on the transmission).

Thus two techiques comprise 1. above: unlocked pulses due to straight interrogation of the set and 2. above: locked pulses were the jammer is tracked using "Ball".

Only in late Feb/Mar 1945 did RAF BC No. 8 Grp and USAAF 8th AF notice increased jamming. RAF No. 60 Grp took ranges and bearings on locked pulses and found originating location was at a known jamming site (location of which not given in report).

Apparently the unit mainly works during the day, according to the report, presumedly because more jamming was encountered then.

5. Aids to Flak

Refers to map captured near Duisburg which basically showed technique whereby Oboe plotting data could be fed in to flak predictors.

The map showed the positions of Allied Oboe stations and thus, the Germans would have to guess which stations were being used at a given time for the technique to work, The report adds that two Oboe sites on the map were at locations were no Oboe station ever existed.

6. GEE

IV LN Reg 351 believed to be involved in tracking and jamming of GEE

7. GEE-H

In Oct 1944, captured equipment finally gave Germans clues about GEE-H system. Some Ali-Baba Gerats then converted to GEE-H frequency. It was thought that by then using "Ball" technique, it should have been possible to commence jamming of GEE-H transmissions but no effective jamming had been encountered to date.

8. SS LORAN

Germans started jamming SS Loran in Feb 1945 using noise modulation. One such jamming station identified was connected by land-line to nearest station of IV LN Regt 351.

9. Route-Tracking & GCI Stations

According to the report, the Germans had held the opinion for some time that analysing correctly the movements of the Mosquito night fighters, especially distinguishing between high and low patrols, would enable them to deduce the intentions of the main bomber force.

In Sep 1944 a special detachment of the German Air Signals Experimental Regiment was provided with "Naxburg" and told to investigate the 10cm AI signals from RAF night fighters. Work of this unit apparently successful as most GCI stations in Western Europe issued with Naxburg and Heinrich sets.

According to the report, the Heinrich sets could be used to D/F the 'Jostle' support aircraft in the bomber streams, carrying jammers on the 38-42 Mc/s band. Thus it was assumed that the GCI stations were taking part in the route tracking of the RAF night fighters and 'Jostle' aircraft, while the actual analysis was still performed in the plotting stations.

10. Use of Listening Receivers in Conjunction with Long Range Radar

In Nov 1944, a number of long-range radar sets (i.e. Wassermann, Mammut) in the coastal sectors were issued with Korfu 812 D/F sets. These were to be used to guide the radar sets onto the bombers and not for route tracking. It was thought that because RAF bombers were forbidden from using H2S until close to the German frontier, the sets were being used to guide the radar on to USAAF 8th AF Bombers during their assembly over the UK.

That's it in a nutshell

Cheers

Rod