Historic California Posts, CampStations
Gualala Radar Site B-75/J-75
by SGM Dan Sebby, Post Historian,
Camp San Luis Obispo
In 1942, the War Department authorized
the acquisition of land on the Ohlson Ranch between the south
fork of the Gualala River and the Pacific Ocean for use as an
air defense radar site. Due to the secrecy surrounding radar
sites, the Site was constructed to resemble farm buildings common
to the coastal regions of California to hide its identity. This
secrecy continued throughout World War II. The Site was not listed
in the War Department Owned, Leased and Sponsored Facilities,
31 December 1945, or any of the Army of the United States
Station Lists published by the Adjutant General of the U.S. Army
as late as 7 May 1946.
The Site was garrisoned by elements of the San Francisco Control
Group of the Fourth Air Force. The mission of this unit was to
detect and identify all aircraft in the unit's area of responsibility
and to direct fighter interceptors to targets deemed to be possible
threats (San Francisco Control Group 1944). A building list,
compiled from a hand-drawn map in Susan Clark's The Del Mar
Ranch: From the German Rancho to The Sea Ranch, California, 1845-1964
and conversation with Russell Ohlson, for the Gualala Radar
Site is presented below.
The 75-mm antiaircraft gun indicated
above was more than likely a .M2 50 caliber Machine Gun or an
M1 40mm Antiaircraft Gun
The site was equipped with the SCR-588
radar set, This was a Canadian-built copy of British long-wave
CHL/GCI system (Type 7 height finder). The Site was initially
garrisoned by the 656th Signal Aircraft Warning Company and was
replaced a detachment from the 653rd Signal Aircraft Company.
Both units were subordinate to the 411th Army Air Force Base
Unit (San Francisco Control Group).
In July 1944, the Site transitioned from
a tactical operation in which it operated 24 hours per day, seven
days per week, to an semi-active or "on guard" status.
In February 1945, the Site was re-designated an "Identification
Friend or Foe" or "IFF" station. IFF Stations
would electronically challenge and identify aircraft entering
or operating in the station's area of responsibility. Aircraft
that did not respond properly were intercepted by fighter aircraft
from supporting U.S. Army airfields.
Beginning in the Spring of 1945, the Site returned to full tactical
status to detect incoming Japanese rice paper balloons that were
armed with incendiary and high explosive bombs. The Site was
responsible for the detection and resulting interception of several
of the over 9,000 balloons launched. The Site remained on full
tactical status until 8 February 1946 when it was returned to
an "on guard" status (411th Army Air Forces Base Unit
The U.S. Army began the process of deactivating the Site on 5
August 1946 when the Headquarters of the San Francisco Control
Group removed all classified materials from the Site. The Fourth
Air Force reported the Site as being surplus to their needs on
24 July 1947. The Site was dismantled and formally transferred
to the District Engineer, USACE for disposal on 28 March 1948
(505th Aircraft Control and Warning Group 1948).
SCR-588 Long Wave Aircraft
Detector and Ground Control Intercept Radar
Fixed medium-range, long wave aircraft detector and GCI. Provides
azimuth, range, and altitude data. Type HR and PPI scopes.
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:
*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.
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.
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.
8 men are operating crew. For 24-hour operation about 54 men
are required to run radar, communication radio, and camp.
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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