Transcript from AIR 23/7762 Public Records Office, Kew

SECRET

PROGRESS REPORT NO. 1 ON R.C.M. INVESTIGATIONS BY AIR COMMAND, SOUTH EAST ASIA.

INTRODUCTION

1. Between 22 January and 29th March, 1944, the two listening Liberators flew a total of 26 sorties from Ceylon to investigate enemy radar transmissions. The two aircraft have usually operated simultaneously in the same general area and have on occasions been accompanied by diversionary bomb carrying aircraft.

2. As a result of the very insistent reports of the operators, the possibility of the use by the enemy of land based radar, having exceptionally long range, was included in the "Interim Report on Japanese Radar Activities in South East Asia."

3. The signals referred to in this report on 43, 53 and 78 megacycles with P.R.F.s varying around 200 cycles per second, were received on a number of occasions at all heights practically throughout flights lasting more than 12 hours.

4. It was only as a result of exhaustive air and ground tests that these signals were proved to be almost certainly spurious. No single satisfactory explanation has been ascertained but it is now reasonably certain that the received signals were due to the combination of British signals beating with pulses generated within the aircraft sets and auxiliary equipment.

r. The special operators with this experience behind them are now much more prepared to differentiate between genuine and false signals. In addition an aural indication is now obtainable in the aircraft to check the P.R.F. of any signal.

6. To co-ordinate the reports of the special operators and to provide technical assistance and guidance, a F/Lt. Technical signals Radar post for duty with the Special Flight has been created and a suitable office posted to fill the vacancy.

7. The flight has been handicapped by the lack of technical spares and suitable test and calibration equipment, which has resulted in discrepancies in the logging of the same signal when received by the two aircraft.

8. In comparing the work of these aircraft with that of aircraft engaged in similar tasks in other theatres, it must be remembered that the return flight from Ceylon to Simalur, for example, involves a flight of over 14 hours. Only a relatively small area can therefore be covered in each flight.

OBJECT OF INVESTIGATIONAL FLIGHTS.

9. The purpose of these investigations is firstly to produce data on which enemy radar cover can be estimated and secondly to obtain the necessary technical information which will led to the introduction of suitable ground or airborne counter measures.

SUMMARY OF OUR PRESENT KNOWLEDGE OF THE USE OF RADAR BY THE JAPANESE

10. LANDBASED. In other theatres, a number of Japanese radar ground stations have been captured, all having the same basic design and similar operation characteristics. The radio frequencies of these sets are of the order of 100 megacycles a with the P.R.F.s between 750 and 1000 cycles per second.

11. Signals have been intercepted in the South West Pacific Area which strongly suggest that the Japanese have additional landbased radar equipment operation on higher frequencies, for aircraft warning, A.A. gun and searchlight control.

12. SHIPBORNE. A Japanese cruiser has been photographed and the aerial system of a radar warning system is plainly visible. Signals intercepted by aircraft when far from land indicate that other Japanese vessels, particularly submarines are fitted with radar.

13. AIRBORNE. Intelligence sources report that a form of A.S.V. is fitted to enemy flying boats of the Emily type. Combat reports and other information continue to increase the suspicion that the Japanese are using or experimenting with a form of A.I. fitted in night-fighters.

Analysis of flight logs.

14. On the earlier flights, some effort was wasted in investigating spurious signals and bad weather made other flights ineffective, but of the 26 flights flown, transmissions which were beyond reasonable doubt of enemy origin, were intercepted during 15 flights.

15. In the following analysis, flights are numbered 1 to 13 with the figure (1) or (2) following to denote the first or second Liberator. The two aircraft normally operate together in the same general area, and to provide a means of checking the received signals, both operators search the same frequency bands. Signals which were almost certainly false have not been included.

Photographic evidence.

16. South Andamans. Good quality photographs exist of the radar installations at Mount Harriett (approximately 3 miles N.W. of Port Blair). Twin radar installations are clearly visible with aerial systems similar to those of the Japanese stations captured at Guadalcanal and Attu.

17. Car Nicobar. Recent P.R. cover of the island is incomplete and still under examination but so far no suspicious installations have been observed.

18. SABANG. The available P.R. cover is 9 months old but a note from C.P.I.S. states that within 1 1/2 miles of the pinpoint given in Flight 9 (2) (05º 53 ' 95º 15') a small oval shaped clearing had been made near the summit of G.Iboih. While no definite installation is visible on the sortie of the 22nd. June, 1943, leveling had taken place, possibly for some future construction. The position affords an unobstructed field of vision except towards the south, where it is obscured by the slightly higher ground forming the actual summit of G.Iboih.

CONCLUSIONS.

19. On the results of far obtained the following conclusions have been reached: -

(1) The Japanese are employing, in this theatre, beam swept ground radar of the Attu or Guadalcanal type.

(ii) This type of installation is certainly installed at Mount Harriett (south Andamans). Similar equipment is almost certainly in operation on Car Nicobar and Sabang, although in the case of the latter there must be some difference as the signal is vertically polarised.

(iii) Watch on Mount Harriett site is continuous and non-continuous on Sabang and Car Nicobar.

(iv) The signals can be received in an aircraft flying about 8,000 ft. up to a distance of 160 miles or more, dependent on whether the beam is sweeping or looking towards the aircraft.

(v) The performance of each individual station has not been completely established but the effective range under favourable conditions is probably of the order of 80 miles.

20. Where no results have been obtained in a given area, e.g., Simalur, it cannot be assumed that no radar exists. The explanation may be that either, the equipment is temporarily unserviceable or alternatively that search was not made on the correct operating frequency band. Such negative results can only be confirmed by photographs and future intensive flight investigations.

Sigs/1106/R.C.M.

23rd, April, 1944