Type 21 General Purpose Radar

Photograph of Type 21 matress antenna

Yomiuri Shimbun. Fair use may apply.


Wavelength 150 cm
Pulse Width 10 microsecond
Pulse Repetition Frequency     
1000 Hz
Power 5 kW
Range 60 nautical miles (100 km) aircraft group
40 nautical miles (70 km) single aircraft
12 nautical miles (20 km) battleship
Mattress: two horizontal sets of four dipoles (transmitter) and two horizontal sets of three dipoles (receiver)
A scope
Accuracy ~1 mile
1-2 km
Resolution 2200 yards/20 degrees
2000 meters/20 degrees
1850 lb
840 kg
Production: Sources disagree on the number of installations, but it appears that Type 21 was first fitted to Ise in 1942-4, Shokaku in 1942-8, Taiyo, Chuyo and Unyo in 1943-1, and others prior to 1943-8, with at least 30-40 sets deployed operationally.

The Japanese Type 21 radar (also known as Mark 2 Model 1 Type 2) was installed on surface ships beginning in August 1943 and was nicknamed the Ship Mattress. Though nominally an air search radar, it was used for  surface search also. Some officers at the Bureau of Naval Construction went so far as to recommend that production of all other types be canceled. A land-based version also existed, known as the Type 1 Model 2, which was known to the Japanese as the Mobile Mattress. Examples of the latter were captured at Roi-Namur and Kwajalein.

The first prototype was installed on Ise just prior to the battle of Midway. The radar was subsequently installed on carriers, battleships, and cruisers. As with other Japanese radars, reliability was shaky, with failure of one of its 54 vacuum tubes all too frequent.  Taiho went to the Battle of the Philippine Sea with one of its two Type 21 radar sets barely operational.


Buderi (1998) (accessed 2007-10-29)

Friedman (1981)
Guerlac (1987)

Lundstrom (2006)

Nakagawa (1997)

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