Transcript from AIR 23/7763 Public Records Office, Kew

PROGRESS REPORT NO. 2 ON R.C.M. INVESTIGATIONS BY AIR COMMAND, SOUTH EAST ASIA

FOREWORD.

This report is divided into two parts, namely, Part I which describes in general non-technical language the results achieved and the difficulties encountered, and Part II which is intended for more detailed study as required by specialist staffs.

PART I

INTRODUCTION

2. Task Investigation Order No. 3 which was issued to Officer Commanding, Special Flight (two Liberator aircraft), specified the areas of search for enemy radar installations as follows:

(i) The enemy coastline from Akyab as far as Mergui.

(ii) Beyond Mergui at the discretion of Officer i/c.

(iii) Area around Bangkok.

3. Two flights to Meiktila were requested at a later date as a result of information which indicated the existence of a radar station in that area.

4. The special Flight moved from Sigiriya to Digri in order to carry out these duties.

5. During the period under review, Headquarters, 20th Bomber Command has been most co-operative in loaning special equipment and Section 22, South West Pacific Area has continued to be the foremost contributor of technical information.

6. This report includes results of flights undertaken up to and including 4th November, 1944.

DIFFICULTIES ENCOUNTERED.

7. The biggest set-back to the investigations was the inability of two aircraft to maintain the scale of effort which is necessary in order to cover the immense geographical area with which H.Q., Air Command, S.E.A. is concerned. As both aircraft normally operated together, in order that the results obtained by one aircraft could be checked against results obtained by the other, both became due for major overhaul and inspection at approximately the same time. Consequently no investigations were undertaken between 21st May and 4th September, 1944.

8. It has become increasingly apparent that the enemy is apt to switch off his radar transmitters if it is thought that an aircraft is remaining in the area for a suspiciously long time. With the equipment in use, depending as it does on a comparison of signal strength received on port and starboard aerials, the task of pin-pointing transmissions has therefore become one of increasing difficulty. It is considered that the only solution to the problem rests in fitting of equipment which will enable actual bearing to be taken, a few bearings will then suffice to pin-point transmissions with a high degree of accuracy.

9. Whenever an enemy radar station is discovered in this theatre, it is the policy of this Headquarters to quote its believed position and co-ordinates after the relevant logs have been analysed. It must be emphasised however that in the majority of cases, the conditions under which the investigating aircraft operate and the equipment employed, preclude exceptionally accurate pin-pointing.

10. Although signals are more likely to be received when the special aircraft accompany other operational aircraft engaged on bombing missions, only a rough indication is normally obtained of the area from which the transmissions originate, and the in-pointing of the transmitter has to be carried out later by the special aircraft working to their own plan.

11. The value of photographic reconnaissance of enemy radar stations in this theatre is restricted by the types of ground radar equipment employed by the Japanese. Whereas a German "Chimney" or "Wurtzburg" is relatively easy to distinguish, the largest type of rada at present known to be used by the Japanese is the comparatively small "Freya" type. Moreover, a very simple transmitting aerial array is used in conjunction with the Japanese 70 megacycle radar which may be suspended from the trunk of a tree, thus to a large extent camouflaging what is normally the most conspicuous element of a radar installation. Low obiques are therefore essential.

12 Periods of up to a fortnight have elapsed between the date of an operation and the date when flight logs have been received at this Headquarters for analysis. It is hoped to reduce this delay, but the limited facilities available to the Special Flight, and the fact that this Headquarters is situated 1,200 miles from Digri, combine to make some delay inevitable.

13. The collation of R.C.M. intelligence from all sources, liaison with other Services, analysis of flight logs, compilation of reports, initiation of establishment action with regard to Special Flight and all other associated R.C.M. matters have been undertaken on a part-time basis by one officer of this Headquarters. It is hoped, however that additional personnel will shortly be available.

14. The installations at Mount Hariett (Andamans), Sabang and Car Nicobar, reported in Progress Report No. 1, have now been confirmed from other sources.

15. One aircraft was lost on the night 10th/11th November, 1944, while probably in the Rangoon area. This was the 52nd mission undertaken by Special Flight.

RESULTS OBTAINED

16. Between 10th May and 22 May, 1944, when the two aircraft became due for inspection, 8 flights were undertaken, in the course of which Mergui, Bassein, Rangoon, Akyab and Mandalay areas were covered. Flying conditions were most unfavourable, but the operation of 70 megacycle radar from Akyab and Rangoon was indicated during this period. In addition, a signal on 127 megacycles, originating in the Moulmein area, was also logged. This signal has not been confirmed by subsequent flights. These results were not published at the time, in view of the new frequency - P.R.F. combinations, and because each frequency was reported once only. Moreover, the individual results of one aircraft did not substantiate or corroborate results obtained by the other.

17. From 4th September onwards flights were flown whenever possible to satisfy the requirements of Task Investigation Order No. 2, and in particular to pin-point the very powerful 70 megacycle type radar installations in the Rangoon area. From time to time this type of signal was logged simultaneously with A.A. and searchlight activity, but in view of the pulse width and information from other theatres, it is not thought that the 70 megacycle radar is employed for any purpose other than that of early warning.

RANGOON AREA.

18. By 25th October, the source of one signal was boxed to the Rangoon area in the immediate vicinity of pin-point 16º 47' 96º 10E. Near this position are three Japanese searchlight sites which have been viewed with suspicion for some time, nevertheless the existence of radar installations at these sites cannot be deduced from available photographs. Two towers, each about 130 feet high, which are situated roughly three miles Nort West of the pin-point specified above, are considered to be of more significance.

MOULMEIN AREA.

19. As mention in para. 15 above, no confirmation has been obtained of the transmission on 127 megacycles. It will be noted that 127 megacycles does not fall within the frequency band of any known type of Japanese radar, although the original German "Freya" operated on this frequency band.

20. Although the pin-point is not absolutely certain, a signal on 68.25 megacycles was boxed to the high ground to the North West of Moulmein, in the vicinity of pin-point 16º 35'N. 97º 32'E. This point is some seven miles south East of the suspected radar sites at Zingyaik Taung Pagoda, concerning which a more detailed photographic analysis has been made. In the opinion of the Headquarters, the site at Zingyaik Taung Pagoda is not operational, and it is exceedingly doubtful whether there is any radar equipment there at all. Paragraph 1 of this Headquarters signal, reference S.253 dated 25th October, 1944, is therefore cancelled, but flight logs are sufficiently conclusive to indicate the existence of a 70 megacycle radar in the general area near 16º 335'N. 97º 32'E.

21. In the course of Flight No. 18, a 200 megacycle enemy radar was boxed to the immediate vicinity of Battery Point Moulmein (16º 30 1/2'N. 97º 37 1/2'E.) Sufficient data is not as yet available to determine the actual function of this radar.

BASSEIN AREA.

22. Efforts to pin-point transmissions received in this area have so far proved unsuccessful. D/F's. have been inconsistent, and on one flight place the source of 70 megacycle type signals out to sea. It is possible that both a 100 megacycle and 70 megacycle radar are installed but no conclusive conclusions can be reached at this stage.

BANGKOK AREA.

22. Three flights have failed to detect any signals in the vicinity of Bangkok, (but see para.24)

MEIKTILA AREA.

24. No signals were detected during three flights, but it must be stressed that where no results have been obtained, it cannot be assumed that no radar exists. Such negative results can only be confirmed by future flight investigations.

PENANG AREA.

25. One 100 megacycle early warning radar was boxed with a high degree of accuracy to an area in the immediate vicinity of 05º 26N. 100º 17 1/2'E. In addition, signals from a 70 megacycle type of radar were also received when the aircraft was near Penang Island. D/F. plotting of these signals is uncertain, and as in the case of the 70 megacycle signal received in the Bassein area, the possibility that the equipment was shipborne cannot be totally excluded.

MERGUI AREA.

26. after four unsuccessful flights to Mergui, Flight No. 18 established the existence of a 200 megacycle radar installed in the vicinity of the Ferry Landing on Mergui Island. (Approximate position 98º 42 1/2'E. 12º 28 1/2'N.)

AKYAB AREA

27. Since the initial flights in this area, 70 megacycle type signals have not re-appeared. Signals on 171, 195, and 210 megacycles have been detected but have not been D/F'd with any degree of certainty.

ANDAMANS.

28. 100 megacycle signals were received which emanated in the area near Port Blair. It is logical to infer from the flight logs that the active transmitter was located at the known site of Mount Harriett.

CLASSIFICATION OF ENEMY RADAR INSTALLATIONS IN A.C.S.E.A. AREA.

29. The following list is based entirely on results obtained by Special Flight No. 159 Squadron, and on photographic evidence. In making this assessment of reliability the following rules have been applied:-

CONFIRMED -A large number of signals have been received devoid of ambiguity which have been D/F'd. to a small specific area. The existence of a radar station in this area has been shown by photographs.

HIGHLY PROBABLY - As for "Confirmed" but not substantiated by photographs.

POSSIBLE - Signals undoubtedly of enemy origin have been received, but owing to their short duration, of for any other reason, have not been accurately D/F'd.

Confirmed 100 Megacycle Early Warning Radar.

Mount Harriett (Andamans).

Sabang

Car Nicobar (Note: signals on 200mc. band have also beeen received.)

Highly Probable 100 Megacycle Early Warning Radar.

Penang.

Highly Probable 70 Megacycle Radar.

Akyab (Not confirmed since 22nd May, 1944.)

Rangoon

Moulmein

Penang Island Area

Highly Probable 200 Megacycle Radar.

Moulmein

Mergui

Possible 70 Megacycle Radar

Bassein Area

Possible 100 Megacycle Early Warning Radar.

Bassein Area.

NOTE ON ENEMY 70 MEGACYCLE RADAR.

30. According to the interrogation report of a Japanese who had operated this type of radar at Noemfoor, prior to capture, the enemy 70 megacycle radar (also variously described as Mk.229 or C.R.I. radar), has a maximum range scale of 300 kilometres.

31. Although the 68.25 megacycle transmission from Rangoon has been reported as being of exceptionally strong signal strength, there has been no evidence to prove that a range of 300 kilometres is actually achieved. It is to be noted however, that the enemy's habit of switching off his transmitters has precluded a detailed range test.

32. Previous reports for this type of radar, received from other sources, quote a practical ground to air range of 75 miles against a single aircraft and 125 miles against an aircraft formation. Experience in this theatre indicates that ranges of this order, and possibly greater, are certainly obtained.

ENEMY 100 MEGACYCLE RADAR.

33. The advance in the Pacific has resulted in the capture of a number of enemy early warning 100 megacycle radar installations. The original Mark 1 Model 1 Radar employs a "mattress" aerial measuring approximately 16 ft. by 18 ft., thus resembling the German "Freya". The range scale of the early models read up to 150 kilometres only (i.e. 94 miles) and it is doubtful whether that range was achieved except under ideal conditions.

34. From captured documents it is believed that an improvement in range has been effected by the introduction of Modification 2 in the Mark 1 Model 1 Radar. Externally the radar installation remains unchanged.

ENEMY 200 MEGACYCLE RADAR.

35. The Japanese Mark 1 Model 2 Radar is probably a later development of the original Mark 1 Model 1 type. The essential difference is in the frequency band which is believed to be from 187 to 205 megacycles. The maximum range of detection achieved by this type of radar is normally quoted as 125 miles for an aircraft formation and 75 miles against a single aircraft. These ranges however are considered to be optimistic. The Mark 1 Model 2 radar is normally mobilised on a 3 ton Army trailer, but instances are known of the equipment being removed and installed on top of a high building in order to obtain greater range.

36. Another Japanese which operates in the 200megacycle band is the Mark IV Model 3 used for searchlight control. This type, or a variant, is thought to be copied from the British S.L.C. Enemy fire control radars, Mark IV Models 1 and 2 are also believed to operate in the 200 megacycle band. The design of the Mark IV Model 1, in particular, is thought to be based on that of the S.C.R.268.

37. Until further information becomes available, it should be assumed that the 200 megacycle radars at Moulmein and Mergui are of the Mark 1 Model 2 type and are therefore used for early warning.

Sigs/1106/R.C.M.

4th December, 1944

PART II

ANALYSIS OF AIRCRAFT LOGS BY FLIGHTS.

PW. - Pulse width in micro. seconds

SP. - Single Pulse.

HP. - .Horizontally Polarised.

VP. -.. Vertically Polarised.

NOTE. Until Pulse Analysers are installed pulse widths quoted must be accepted as approximate and should therefore be treated with reserve.

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