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Old 14th February 2010, 02:21
RodM RodM is offline
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Using Y-Intercepts to research the Luftwaffe

Hello One and All,

stimulated by Nick Beale's authorative thread on ULTRA, this is an attempt to kick-start discussion on the availability and use of other archived British Y-intercept material. Firstly, because my own interest concerns the Nachtjagd in the late-war period, I have not actively investigated the availability of such information on other arms of the Luftwaffe or the availability and quality of such material in the 1939-43 period.

I will start by stating that A.I. (British Air Intelligence) produced a large number of reports based upon the collated intelligence from wireless intercepts and captured documents and aircrew. The attached PDF entitled 'Air Ministry AI Document Distribution List' surveys the type and scope of these reports. The document is a reproduction of a document found on an A series (A5400 from memory) microfilm held by The Air Force Historical Research Agency. It lists the A.I. reports being distributed to American commands by originating directorate. I have added known British National Archives file reference numbers for surviving copies of these reports. The various surviving reports held by the British National Archives are by no means neatly organised, easy to locate via an archive catalogue search, or complete.

A tremendous amount of Y-intercept material survives in the series AIR 51 - Mediterranean Allied Air Forces: Microfilmed Files. There appears to be material of wider interest in these microfilms, beyond just operations in the Mediterranean. The attached PDF entitled 'AIR 51 Int Sigint Index' provides a list of the Signals Intelligence files held within this microfilmed series. Others, such as Nick Beale, would be more qualified to comment on the general content of these files. The microfilm AIR 51/292 holds an incomplete selection of A.I. reports in the BAT, OWL-ROBOT, Pearl/Zip/FT/AI, Pearl/Zip/GAA, Pearl/Zip/GAM, Pearl/Zip/LS, and Pearl/Zip/TAC/N series, and I have indexed these in the AIR 51 PDF. I would expect that other microfilms contain a wider selection of reports.

Of wider interest are the daily Air Activity Summaries as prepared by A.I.4 throughout the war. A complete set of these documents is held at the British National Archives (there are also weekly summaries, but I haven't looked at these):

AIR 22/476-503 Air Ministry W/T Intelligence Service Daily Summaries Nos. 1-2076 (28 Volumes) September 1939-May 1945

At least in the late-war period, these reports cover a 24-hour period ending at 0600 hrs B.S.T. or 0700 hrs B.D.S.T., depending on the time zone in use.

The documents contain:

An executive summary on the first page of (a) Enemy Bomber Activity, and (b) Enemy Nightfighter Activity. Sometimes other information of interest, such as Y evidence of lost aircraft is also appended.

Part I - Enemy Bomber and Reconnaisance Activity. This section has information under the following column headings Unit; A/C (i.e. the number of aircraft heard); Times; Control (i.e. the ground control with which the aircraft were operating); Freq (i.e. wireless frequency); Remarks.

Part II - Enemy Bomber, Fighter Bomber and Miscellaneous Activity (V.H.F.) - when present, I presume that the format of the information is similar to Part III. below.

Part III - Enemy Fighter Activity (Day). this section contains the following sub-sections: 1. GAF reaction to Strategic Operations, GAF reaction to Tactical Operations, and 2. information on aircraft (usually nightfighters) heard operating during the day. Part one is usually in a narrative style with a summary of Allied operations, but can include specifics such as times, type and number of aircraft heard to be operating, location, along with instructions passed.

Part IV - Enemy Fighter Activity (Night). This section contains the following sub-sections: 1. Narrative of reactions to specific raids, and 2. Summary of messages intercepted and information on aircraft heard operating during the night.

Anyway, this will do for a start. If anyone has further information on the Y material available, especially in non-British archives, I would be very interested to heard from you. As with ULTRA, this material in isolation does not provide some magical all-encompassing view of Luftwaffe operations and organisation, but can combine well with information from all documentary sources. Then S/L G.R. Scott-Farnie, head of Y Section in Air Intelligence early in the war once summed it up beautifully: "Intelligence is rarely dramatic - the best results are obtained from the continous study of details, which although singularly of little value are collectively of great importance."



I've added samples of some late war reports concerning Luftwaffe activity on 7 April 1945.

The files are:

Pearl-Zip-BMP-D-844.jpg - the main narrative page from the Pearl/Zip/BMP/D report concerning daylight LW reaction to Allied raids. The D Reports at this stage of the war appear to be quite sparse, and certainly not as detailed as the N Reports. The report is contained in HW 13/86 at The National Archives, Kew.

Activity Summary No 2045 Pg 2.jpg & Activity Summary No 2045 Pg 2.jpg - two pages from the report described above. The report is contained in AIR 22/503 at The National Archives, Kew.
Attached Images
File Type: jpg Pearl-Zip-BMP-D-844.jpg (139.5 KB, 264 views)
File Type: jpg Air Activity Summary No 2045 Pg 2.jpg (170.3 KB, 255 views)
File Type: jpg Air Activity Summary No 2045 Pg 3.jpg (182.4 KB, 162 views)
Attached Files
File Type: pdf Air_Ministry_AI_Document_Distribution_List.pdf (20.5 KB, 194 views)
File Type: pdf AIR_51_INT_SIGNINT_INDEX.pdf (33.7 KB, 190 views)

Last edited by RodM; 14th February 2010 at 11:57. Reason: added info
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