Transcript from AIR 23/7762, Public Records Office, Kew.

MOST SECRET

Interim Report on Japanese Radar Activities in South East Asia Area

INTRODUCTION

1. A total of 8 sorties has been flown by two special Liberators based at Sigiriya to investigate the use by the Japanese of radar equipment on the Andaman Islands.

2. The special receiving equipment has been handled by three Wireless Operator/Air Gunners with practically no previous experience of this type of work or of the equipment installed in the aircraft. It is necessary therefore to treat with reserve any reports rendered on these flights until further experience has been gained.

3. due to the inability of the aircraft to D/F or to "home" on enemy transmissions it has not yet been possible to pinpoint or to define the location from which the transmissions have emanated.

4. Not withstanding the limitations mentioned in paras. 2 and 3 above, some very valuable data hs been submitted for analysis as a result of these flights.

5. It must be emphasised that when using a superheterodyne receiver such as the S27D, spurious signals or harmonics may be received. Where it was obvious that such signals were logged these have been ignored in the compilation of this report.

6. Where only one intercept of a frequency has been obtained, this intercept has been ignored until confirmation becomes available from future flights.

MAIN FREQUENCIES REPORTED.

7. The following frequencies are those on which signals were reported a number of times:-

(i) 43 Mcs. Approximately 20% of the intercepts deal with signals on this frequency which had obviously attracted the attention of the operators owing to the range at which these signals were received and the signals strength. When searching, the signal which is vertically polarised sweeps rapidly and is reported to have held the aircraft at a distance of 250 miles from enemy territory. The majority of the intercepts quote the P.R.F. as being approximately 200, in a few cases the P.R.F. is given as 100. On this frequency, as on others, two signals having the same radio frequency, but with different P.R.F.'s, (one approximately half the other), were logged.

(ii) 48.5 Mcs. Reported by both aircraft on the same sortie as a horizontally polarised long range signal.

(iii) 52.5 - 54 Mcs. About 10% of the intercepts were within this frequency band. Signals on 53 Mcs. Are described as sweeping rapidly and as hoding the aircraft at long range with a fairly constant P.R.F. of approximately 210. One report specifies the signal on 53 Mcs. As frequency modulated.

(iv) 72 Mcs. Steady clear pulse holding aircraft upt to 15o miles. Horixontally polarised, sweeping when much nearer enemy territory, P.R>F's on this frequency varied between 130-230.

(v) 78 - 89 Mcs. Activity within this band was reported on 5 different frequencies. On 78 Mcs. A sweeping signal was received at good signals strength 200 miles from enemy territory. Two P.R.F's of 206 and 100 were logged.

(vi) 95.2 Mcs. Shorter Range Horizontally polarised signal sweeping and then holding with P.R.F. approximately 200.

(vii) 96.5 Mcs. At the time this signal was logged, the investigating aircraft was intercepted by an enemy night fighter. This interception together with the apparent increase in signal strength convinced the operator that the signal emanated from Japanese A.C.

Note. (a) The aircraft was immediately over enemy territory at the time of interception in an area where ground radar has for some time been suspected.

(b) 96.5 is in the frequency band known to be employed by Japanese ground radar sets.

8. CONCLUSIONS.

(i) Really positive conclusions cannot be drawn from an analysis of this type with only a limited amount of information available but it is considered that the reports definitely indicate a much more extensive use of radar by the enemy in this theatre than was expected. In addition these preliminary investigations have limited the frequency bands for future detailed examination.

(ii) In the light of the information obtained from these flights the operation of A.I. by the enemy must be considered as a very likely possibility, it has yet to be proved however that enemy A.I. operates on frequencies between 92 and 105 Mcs.

(iii) Many more investigational flights are required to estimate the radar cover afforded by radar equipment installed in the Andaman Islands and in other territory occupied by the enemy in the South East Asia Area.

Sigs/1105/RCM

19 February, 1944