Historic Posts, Camps, Stations and Airfields
San Clemente Island Radar Sites B-3 and B-4/J-4
by Sgt Maj (CA) Dan Sebby, Military Historian,
Two Army Air Forces radar sites located at the northern end of San Clemente Island during World War II. Site B-3, Located at the Fleet Training Center, was equipped with the SCR-270B Mobile Long Wave Aircraft Warning radar set while Site B-4/J-4, located at China Point, was also equipped with the SCR-270B and later the SCR-588 Long Wave Aircraft Detector and Ground Control Intercept Radar set. Both sites were subordinate to the Los Angeles Control Group. The site consisted of at least three parcels, two for the radar equipment, and at least one cantonement area for the soldiers' housing, feeding and administration.
Radar Site B-3 consisted of 11.61 acres while Radar Site B-3 consisted of 6.42 acres. The cantonement area for Site B-3 measured 9.97 acres. The location of this area is not currenlty known. It is not known if Site B-4/J-4 shared the contonement area or had a separate area.
Location coordinates:
Radar Sets on San Clemente Island
SCR-270-D Mobile Long Wave Aircraft Warning Set (Radar Sites B-3 and B-4)
Description: Six-vehicle mobile, long wave early warning aircraft detector. Azimuth and range supplied. Set is equipped with "A" scope.
Uses: To establish a screen of warning which provides information of approaching aircraft as early as possible but with a sacrifice of accuracy in range, azimuth and elevation. IFF equipment RC-150 is used.
Performance and Siting: Maximum range on a single bomber flying at indicated heights, when set is on a flat sea level site:
 Altitude, feet  1,000  5,000  20,000  25,000
 Range, miles  20  50  100  110
Set should be sited at a height between 100' and 1000' above an unobstructed reflecting surface.
Transportability: Complete set is carried in 6 vehicles, the largest of which measures 30'4" x 9'10" x 8'. Total weight of shipment is 101,790 lbs; total volume 11,485 cu. ft.
Installation: Operates from trucks in which mounted. Can be placed in operation about 6 hours after arrival at site.
Personnel: Seven men comprise operating crew. For 24 hour operation about 50 men are required to run radar, communication radio, and camp.
Power: 15.3 KW, supplied by PE-74, 25 KVA gasoline-driven generator, having fixed consumption of 4 gal. per hour, non-leaded gasoline.
SCR-588 Long Wave Aircraft Detector and Ground Control Intercept Radar (Radar Site J-4)

Description: Fixed medium-range, long wave aircraft detector and GCI. Provides azimuth, range, and altitude data. Type HR and PPI scopes.
Uses: To give continuous plan position and accurate relative height of enemy plane and friendly fighter plane for GCI. Set can also be used for early warning and to give increased coverage at low angles of search. IFF equipment RC-188 is used. When operating as GCI, VHF equipment SCR-624 is required.
Performance and Siting: Maximum range on a medium bomber, with set on flat sea level site:
 Altitude, feet




 Range*, miles




*Range of PPI limits GCI operation to about 45 miles.
When operating as GCI, set must be sited so that a flat unobstructed surface extends at least 1/4th mile in the height-finding sector. Good GCI sites are extremely rare. For early warning, sets should be sited between 100 and 1,000 feet above an unobstructed surface.
Transportability: Set is packaged for shipment in 55 units, weighing a total of 54,000 lbs. Largest unit measures 15.3' x 3.8' x 1.8'. Total shipping space is 3500 cu. ft.
Installation: Requires a weatherproof building approximately 20' x 40' for housing radar components and a building approximately 20' x 20' for power units and switchboard. A 25' tower on concrete footing is required for support of antenna. Buildings and tower can be built by Engineers in about 3 weeks. Radar can be installed by 5 men in 2 weeks.
Personnel: 8 men are operating crew. For 24-hour operation about 54 men are required to run radar, communication radio, and camp.
Power: 4 KW at 230 volts and 1 KW at 115 volts, from three PE-198 electric diesel units, supplied with set. (Two units operate simultaneously). Fuel consumption is 21/2 gals. of Diesel fuel oil per hour.
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Updated 4 May 2016