This is from "The History of US Electronic Warfare, Volume 1" by Alfred Price
THE DEVELOPMENT OF RADAR IN JAPAN, TO THE END OF WORLD WAR II
Sources: US official report ‘A Short Survey of Japanese Radar” by the Operations Analysis Section and the Air Technical Intelligence Group of the Far East Air Force, dated November 20, 1945. (Ref. AOC Doc. 32). Declassified February 1962. Royal Air Force Signal Intelligence Report “Japanese Radar Equipment,” November 30, 1944.
Note: Only the more important radars are described in the account which follows.
The development of radar in Japan dates from 1936, when Professor K. Okabe at the University of Osaka began work on an electronic method of detecting aircraft. Working under the famous Dr. Yagi (who gave his name to the Yagi antenna), Okabe concentrated on the development of a bistatic system with a separated transmitter and receiver, to detect the interference to radio signals caused when an aircraft passed between the two. The method of operation was, therefore, the same as that tried at the US Naval Research Laboratory in the 1920s and early 1930s, but which had already been overtaken by pulsed systems. Unlike the work in the US, however, the Japanese were to continue the development of the interference detector in parallel with that of pulsed radars. To differentiate between the two systems, the Japanese referred to the interference detector as the Type A equipment and the pulsed radar as the Type B. Okabe saw the great advantage of the Type A equipment to be that, compared with a pulsed system, for a given transmitted power, far greater detection ranges could be achieved. Since low transmitter power was to dog the Japanese radar program throughout the conflict, this was an important consideration. The great drawback of the interference detector was that it did not give the position of the aircraft along the line between the transmitter and the receiver, and despite much hard work, the Japanese team was never able to resolve this fundamental problem. After a lot of experimentation, the Type A system went into production in 1940, operating in the 40 to 80 MHz band and using transmitters developing between 3 and 400 watts. During 1941, the Type A entered service with the Japanese Army and was deployed in quite large numbers. In all, about a hundred of these equipments were built and they remained in service until the end of the war. The longest Type A line of detection was from Formosa to Shanghai, a distance of more than 400 miles.
Japanese work on the development of pulsed radar began in 1941, with completely separate programs by the Army and the Navy, which resulted in a considerable waste of effort to produce different radars of similar (and, compared with those of the Allies), low performance. Because of their separate lines of development, the Army and Navy programs will be described separately in this account.
The Japanese Army radars followed a fairly logical designation system. Each equipment had a type number preceded by Tachi, meaning land-based (“chi” from tsuchi meaning “earth”), Tase meaning ship-borne (“se” from misui meaning “water”), or Taki meaning air-borne (“ki” from kuki meaning “air”). In each case, the type designation was prefixed “Ta” from “Tama Institute,” the Army’s research institute near Tokyo.
The first Army radar to go into production was the Tachi-6 static early warning set which operated on frequencies in the 68 to 80 MHz band. This unusual radar employed a transmitter with an omnidirectional or wide-angle antenna, and three or four separate receivers each with rotatable directional antennas to search for echoes from targerts this can be compared in principle, to lobe-on-receive only. a technique reintroduced in more recent times as a means of making tracking radars less vulnerable to electronic jamming. The first Tachi-6s were deployed in 1942, and gave ranges up to 185 miles on high flying aircraft. (Production of Tachi-6 is estimated at 350).
Following the Tachi-6, came the only slightly less cumbersome (18 ton) but transportable Tachi-7 for the same purpose, operating on frequencies around 100 MHz and with a maximum range similar to that of the earlier set. About 60 Tachi-7s were built and from October 1943, these were deployed throughout the home islands and occupied territories. For service in the combat zone, a yet lighter set was needed, and early in 1944, the 4-ton Tachi-18 appeared which also operated on frequencies around 100 MHz. (Total production is not known).
None of the early warning radars mentioned above could give indications of altitude, so the Tachi-20, which operated on frequencies in the same band as the Tachi-6, was developed. This set did not go into service until March 1945, and about a dozen were deployed. The Tachi-35, operating on 82 MHz, entered service for the same purpose in May, and only a few were deployed before the war ended.
Japanese Army work on the development of precision radars for searchlight and AA gunlaying received a considerable boost early in 1942, following the capture of the American and British bases at Corregidor and Singapore. At Corregidor, the Japanese captured an intact SCR-268 and a badly damaged early warning radar, probably an SCR-270. On Singapore, they captured badly damaged examples of an early warning set and a gunlaying radar, and also found some useful technical manuals which had not been destroyed.
As a result of these finds, two Japanese searchlight and fire control radars appeared, the Tachi-1 and the Tachi-2, both operating on frequencies around 200 MHz and employing many techniques copied from the SCR-268. The reason for the two different radars was that two companies, Sumitomo (Tachi- 1) and Tokyo Shibaura (Tachi-2) had each received a contract to develop an AA gunlaying radar (a further example of the fragmentation of effort which characterized the Japanese radar program at this time). Neither radar was successful, however, and in total only 65 were built. Sumitomo then switched production to the Tachi-3 (72 to 84 MHz) based on the British Gunlaying Mark II radar. About 150 of these were built, and it became numerically the most important Japanese set in this category.
The Tachi-4 was a mobile set intended to replace the Tachi-2 and operating on the same frequencies, but it was unsuccessful and saw little use. However, a development of the Tachi-4, the Tachi-3 1, proved much more successful. About 70 had been built by the end of the war. It had become the most important precision radar operating in the 200 MHz band.
From the beginning of 1944, the Tama Institute worked to produce a Japanese Army version of the German Wuerzburg radar, one of which had been delivered to Japan by submarine. Before it could go into mass-production, however, it was decided to re-engineer the set to Japanese specifications. As a result of this and the severe disruption in production caused by the B-29 attacks, the Tachi-24, as the set became known, was still in the prototype stage when the war ended.
The only Japanese Army airborne radar to go into mass production was the 150 MHz Taki-1 ship- search equipment, installed on maritime patrol aircraft and torpedo bombers. This radar first saw operational use in the fall of 1944.
As has been said, the development of radar for the Japanese Navy proceeded entirely separately from that for the Army. There was even a security barrier between the two programs to maintain this separation. Thus, the Nihon Musen company, one of the three principal Japanese concerns producing radar during the war, had to divide its main plant at Mataka near Tokyo into two when building equipment for the two services. There was even a ban preventing company engineers working on the different contracts from exchanging information.
The Japanese Navy system of designating radars was quite different from that used by the Army. Sets were categorized by purpose. Thus, the Mark I radars were all ground early warning sets; the Mark us were ship-borne sets, the Mark IVs were ground precision radars for searchlight and/or AA gunnery control and the Mark VIs were airborne ship-search equipments. A notable departure from this system was the Gyoku-3 designation for the Navy airborne interception radar.
The main research and development agency for Navy radars was the Second Naval Technical Institute near Tokyo. The first Navy set to go into production was the Mark I Model 1 early warning radar which operated on frequencies around 100 MHz. The first of these to become operational was installed at Rabaul in the spring of 1942, and altogether about 80 were delivered. The next set in this category to enter production was the Mark I Model 2, a mobile radar operating on frequencies around 200 MHz; about 300 of these were built. This set in its turn was followed into production in 1943, by the lightweight Mark I Model 3 operating on frequencies in the 147 to 165 MHz band. About 1,500 were built and it saw widespread use. The reader will note the many similarities between this family of early warning radars, and the quite separate family developed for the same purpose by the Army.
The first Japanese Navy shipborne radar, the Mark II Model 1 operating on frequencies around 200 MHz, began sea tests on the battleship Ise in March 1942. A few months later, the radically different Mark II Model 2 appeared, operating on frequencies in the 3,000 MHz band and using a 2 kW magnetron as power source (it is interesting to note that at the beginning of 1942, Japanese work on microwave radar was only a few months behind that in the USA, though the gap increased rapidly during the course of the war). Several hundred of these microwave radars were built during the conflict, and versions were installed on submarines and ships of all sizes. The Navy re-engineered its own version of the German Wuerzburg and re-designated it the Mark II Model 3. As in the case of the Army version, however, this radar was only in the prototype stage when the war ended. The Mark II Model 4 was a lightweight set operating on frequencies around 150 MHz and installed on small ships and submarines. In most cases, these ship-borne radars were intended to provide air and surface warning, with antiaircraft and surface gunnery control as an auxiliary function. This requirement for radars to perform conflicting functions was beyond the capability of Japanese technology at the time, and resulted in sets whose performance was mediocre in most respects.
For the control of the searchlights and antiaircraft guns defending its shore bases, the Japanese Navy developed its own version of the SCR-268, the Mark IV Model 1, which also operated on frequencies around 200 MHz. The first of these went into operation at Rabaul in November 1943, and in all 80 were built. Following this set in production, was the Mark IV Model 2, with several improvements to make it easier to build and maintain. The Mark IV Model 3 was a direct copy of the Army’s Tachi- 1 (and a rare example of inter-service cooperation). The Navy found it as unsatisfactory for searchlight control as the Army had for gunnery control, however, and only a few were built.
Towards the end of 1941, the Japanese Navy began work on a lightweight ship-search radar for its patrol aircraft. This resulted in the Mark VI series of equipments operating on frequencies around 150 MHz, which first entered service in 1943. Altogether, some 2,000 examples of this radar were built and the set saw wide scale use.
When the war ended, the Navy had under development an airborne intercept radar for night fighters: the 150 MHz Gyoku-3. Although tests had begun, the radar was too late to see action.
The picture of Japanese radar development throughout and up to the end of World War II is one of piecemeal development, and of sets, which in most cases, brought little improvement in capability over their predecessors. The need to run almost completely separate and parallel radar development programs for the Army and the Navy reduced the effectiveness of the nation’s limited radar research effort, and individual services even placed contracts with different companies to produce radars to do the same job. The outcome was that the small Japanese electronics industry found itself required to turn out relatively small production runs of many different types of radar. It proved quite impossible to keep pace with the quantity and quality of Allied radar development and production. The large scale use of countermeasures against the Japanese radars did not begin until April 1945, and in the four months between then and the end of the war, there was no time to react effectively. The impact of US jamming on the Japanese air defense system is covered in Appendix H.
DETAILS OF THE MAIN TYPES OF JAPANESE RADAR
Note: Because most of these radars ran to numerous models and sub-types, the technical details given below should be regarded as representative for the type only.
Type A Bi-static Doppler Interference Detector.
Quantity built about 100 Power — 3, 10, 100 and 400 watt versions.
First used 1941
Maximum range up to 440 miles
Frequencies 40-80 MHz
Note: although strictly speaking this equipment was not a radar, it has been included in this list for
Tachi-1 Ground Searchlight and AA Fire Control Radar
Quantity built 30 Peak power 5 kW
First used 1943 Pulse Length (approx.) 2 microsecs
Maximum range about 12 miles PRF (approx.) 1,000
Frequencies used: around 200 MHz
Tachi-2 Ground Searchlight and AA Fire Control Radar
Quantity built 35 Peak power 10 kW
First used 1943 Pulse Length 2 microsecs
Maximum range about 25 miles PRF 1,000
Frequencies used: around 200 MHz
Tachi-3 Ground Searchlight and AA Fire Control Radar
Quantity built about 150 Peak power 50 kW
First used 1944 Pulse Length 1, 2 microsecs
Maximum range about 25 miles PRF 1, 2 thousand
Frequencies used: 72 to 84 MHz
Tachi-6 Static Early Warning Radar
Employed omni-directional or wide-angle transmitter antenna, and up to four separate directional and movable receiver antennas.
Quantity built 350 Peak power 10-50 kW
First used 1942 Pulse Length 25-35 microsecs
Maximum range 185 miles PRF 500 or 1,000
Frequencies used: 68 to 80 MHz
Tachi-7 Transportable Early Warning Radar
Quantity built about 60 Peak power 50 kW
First used 1943
Maximum range 185 miles
Frequencies used: around 100 MHz
Tachi-18 Mobile Early Warning Radar
Quantity built 400 Peak power 50 kW
First used 1944
Maximum range 185 miles
Frequencies used: 94 to 106 MHz
Tachi-31 Ground Searchlight and AA Fire Control Radar
Quantity built 70 Peak power 50 kW
First used 1945
Maximum range 25 miles
Frequencies used: 187 to 214 MHz
Taki-1 Airborne Ship-search Radar
Quantity built about 1,000 Peak power 10 kW
First used 1944
Maximum range about 60 miles against a large ship
Frequencies used: around 150 MHz.
Mark I Model 1 Static Ground Early Warning Radar
Quantity built about 80 Peak power 5 kW
First used 1942 Pulse Length 10-30 microsecs
Maximum range about 90 miles PRF 530-1,250
Frequencies used: 92 to 108 MHz
Mark I Model 2 Transportable Ground Early Warning Radar
Quantity built about 300 Peak power 5 kW
First used 1942 Pulse Length 3-20 microsecs
Maximum range about 90 miles PRF 750-1,500
Frequencies used: 187 to 214 MHz
Mark I Model 3 Portable Ground Early Warning Radar
Quantity built about 1,500 Peak power 10 kW
First used 1943 Pulse Length 3-12 microsecs
Maximum range about 90 miles PRF 400-600
Frequencies used: 146 to 165 MHz
Mark II Model 1 Shipborne Air and Surface Search Radar
First used 1942 Peak power 5 kW
Maximum range 90 miles for aircraft,18 miles against large ship Pulse Length 3-20 microsecs
Frequencies used: 185 to 210 MHz
Mark II Model 2 Shipborne Surface Search and Fire Control Radar
Quantity Built 400 Peak power 2 kW
First used 1942 Pulse Length 2-10 microsecs
Maximum range 22 miles against large ship PRF 2,500
Frequencies used: 2,857 to 3.125 MHz
Mark IV Model 1 Ground Searchlight and AA Fire Control Radar
Quantity built 80 Peak power 30 kW
First used 1943 Pulse Length 3 microsecs
Maximum range 30 miles PRF 2,000
Frequencies used: around 200 MHz
Mark IV Model 2 Ground Searchlight and AA Fire Control Radar
Improved version of the Mark IV Model 1
First used 1944 Peak power 30 kW
Maximum range 30 miles Pulse Length 3 microsecs
Frequencies used: around 200 MHz PRF 1,000
Mark VI Airborne Ship-search Radar
Quantity built more than 2,000 Peak power 3-6 kW
First used 1943 Pulse Length 3-10 microsecs
Maximum range 43 miles against a PRF 700-1,200
Frequencies used: 140 to 160 MHz