The Pacific War chapter (chapter 15) of SUMMARY TECHNICAL REPORT OF DIVISION 15, NDRC, VOLUME 1, RADIO COUNTERMEASURES stated the following regards Japanese radars in the Okinawa area.
Page 332 --
The final incident in the story of ship-borne countermeasures against enemy ground radar
came with the planning and execution of the invasion of Okinawa. An elaborate reconnaissance
of all features of the enemy defense in the Okinawa-Gunto had been carried out before
definite plans were consummated for Operation Iceberg. This reconnaissance had included radar
intercepts by aircraft, surface vessels, and submarines, as well as small-space and large-scale
photographic reconnaissance's permitting detailed pin points of several radar sites. Assessment
of this information revealed that the enemy's radar defense was probably limited to
EW equipment. A total of 10 to 12 such sets was eventually found, including the 7 listed
below:
2 Mark I Model 3
2 Mark I Model 1
2 Mark B
1 Mark CHI
In planning the operation, past experience, including Iwo Jima, strengthened the conclusion
that ship-borne jamming of EW ground radars would serve no useful purpose. Accordingly,
the operational order specified the conventional 24-hr intercept guards, with the addition
of definite jamming plans for protection against enemy airborne radar. (See subsection
entitled "Surface Vessels" of Section 15.5.4.)
and later:
Pages 333 - 334
As an adjunct to this function, the conventional intercept guards were maintained in order to discover, if possible,
the operating procedures which governed the use of enemy EW radar. Apart from the examples
of the preceding paragraph, this intercept operation further assisted by eliminating
a particularly annoying Mark CHI radar. It was discovered that this radar in the vicinity of
Chinen Saki was being used deliberately to jam the voice communication circuit of the TBS
equipment operating at 72.2 mc. Direction-finding fixes obtained from the TDY rotating antenna
were sufficient to permit low-level reconnaissance photographs to pin-point the enemy
set, and naval gunfire put it out of action.
To put the quoted passages above in context, bear in mind the following facts:
-The "CHI" radar listed below is the wartime US Navy code name for the post-war intelligence name "Tachi-6,"
-The Japanese Mark I radars transmitted on the same frequencies as SC and SK meterwave early warning radars on American
carriers and other surface ships,
-The "Tachi-6" broadcast on the same frequency as the US Navy's TBS ship-to-ship radios.