Mill Valley Air Force Station

Mill Valley Air Force Station (1951-1980) - A Cold War Air Force Radar Station first established as Mount Tamalpais Air Force Station in 1951 near Mount Tamalpais, Marin County, California. Renamed Mill Valley Air Force Station on 1 Dec 1953 after the nearby location. Initially assigned a Permanent ID of P-38 and later a Sage ID of Z-38. Abandoned in 1980. Site also housed Nike Missile Site SF-90DC.

Mill Valley AFS Radome 411 Empty FPS-26A Tower
Mill Valley AFS Operations Bldg. 408 & FPS-66A Search Radome Bldg. 409

History of Mill Valley Air Force Station

Established in 1951 and became operational in 1951 as Mount Tamalpais Air Force Station manned by the 666th AC&W Squadron. The station initially had both a Ground-Control Intercept (GCI) and early warning misssion. The early warnng mission involved tracking and identifing all aircraft entering their airspace while the GCI mission involved guiding Air Force interceptors to any identified enemy aircraft. Controllers at the station vectored fighter aircraft at the correct course and speed to intercept enemy aircraft using voice commands via ground-to-air radio. The station was renamed Mill Valley Air Force Station in 1953.

Initial equipment included two CPS-6B radars. In 1955 the site received an FPS-8 that was later upgraded to a GPS-3. In 1956 an FPS-4 height finder radar operated here. In 1958 the FPS-4 was replaced with an FPS-6 height finder.

The transition of the manual GCI system to the automated SAGE system began with the installation of the FST-2 coordinate data transmitter and search radar upgrades. The FST-2 equipment digitized the radar returns and transmitted the digital returns to the SAGE direction center. Under the SAGE System, interceptor aircraft were directed to their targets by the direction center computers and controllers, greatly reducing the need for local controllers and equipment at every radar station.

The FST-2 was a very large digital system using vacuum tube technology. Over 6900 vacuum tubes were used in each FST-2 requiring 21 air-conditioned cabinets, 40 tons of air conditioning, 43.5 kva of prime power, and usually a large new addition to the operations building. The FST-2B modification added two more cabinets but with newer solid-state (transistor) technology to process coded responses from aircraft transponders.

The site began operation as a SAGE site in 1960 initially feeding the Beale SAGE Direction Center DC-18. The search radar was upgraded to an FPS-7C with one FPS-6 height finder and one FPS-6B height finder radar installed. The FST-2 was installed between March 1960 and June 1960. This was the baseline configuration as the site began SAGE operation. In 1964 an FPS-26A height finder radar replaced the FPS-6. The FPS-6B height finder was upgraded to an FPS-90.

With the closure of Beale SAGE Direction Center DC-18 on 1 Aug 1963 control of Mill Valley AFS switched to the Adair SAGE Direction Center DC-13. DC-13 closed in 1969 and control switched to the Luke SAGE Direction Center DC-21.

In 1966 the FPS-26A was converted to an FSS-7 SLBM detection & warning radar operated by Det 3, 14th Missile Warning Squadron.

Mill Valley AFS was responsible for the maintenance of one remote unattended gap filler radar site. The gap filler sites were placed in locations where the main search radar lacked coverage. Maintenance teams were dispatched from Mill Valley AFS for regularly scheduled maintenance or when fault indicators suggested the site had problems. The Mill Valley AFS gap filler radar was located at Fort Ord between 1954-1955 as a manual site and was not integrated into the SAGE System.

In the 1970s the FST-2 was replaced with a more up-to-date coordinate data transmitter, the FYQ-47 (Common Digitizer).

Between 1960 and 1971 Mill Valley AFS hosted the Army Air-Defense Command Post (AADCP) SF-90DC. The command post was initially an FSG-l Missile-Master Radar Direction Center, later equipped with the TSQ-51 Missile Mentor solid-state computer system. The command post was integrated into the SAGE System and provided coordination between the U.S. Army Nike sites and the SAGE direction center.

On 1 Oct 1979 Mill Valley AFS came under TAC jurisdiction and was subsequently closed and abandoned by the Air Force on 30 Sep 1980 when the FAA assumed operational control of the site.

The physical plant of the site was divided into a main site, a cantonment area, a housing area and a radio site. The main site housed the operations buildings, the radar towers, and the backup generators. The cantonment area housed the enlisted barracks, the bachelor officer's quarters, the orderly room, the dining hall, the motor pool and other support buildings. Apart from the main site was a small housing area for married personnel. A separate Ground to Air Transmitter/Receiver (GATR) radio site located at Beale AFB housed the radio equipment for directing aircraft intercepts.

Mill Valley AFS Major Equipment List Search Radar HF Radar Data Systems CPS-6B FPS-8 GPS-3 FPS-7C FPS-66A ARSR-4 FPS-4 FPS-6 FPS-6A FPS-26A FSS-7 FPS-116 FST-2/A/B FYQ-47

Unit Designations 666th Aircraft Control & Warning (AC&W) Squadron (1951-1961) 666th Radar Squadron (SAGE) (1961-1974) 666th Radar Squadron (1974-1979) 666th Radar Squadron (TAC) (1979-1980)

666th Assignments

1 Jan 1951 - Assigned as the 666th Aircraft Control & Warning (AC&W) Squadron at Mount Tamapalis CA 1 Jan 1951 - 6 Feb 1952 Assigned to 542nd AC&W Group 6 Feb 1952 - 1 Jul 1960 Assigned to 28th AD 1 Jul 1960 - 1 Aug 1963 Assigned to San Francisco ADS 15 Jan 1961 - Redesignated 666th Radar Squadron (SAGE) 1 Aug 1963 - 1 Apr 1966 Assigned to Portland ADS 1 Apr 1966 - 15 Sep 1969 Assigned to 26th AD 15 Sep 1969 - 19 Nov 1969 Assigned to 27th AD 19 Nov 1969 - 30 Sep 1980 Assigned to 26th AD 1 Feb 1974 - Redesignated 666th Radar Squadron 1 Oct 1979 - Redesignated 666th Radar Squadron (TAC) 30 Sep 1980 - Deactivated

Mill Valley AFS Gap Filler Radar Sites (edit list)

ADC	NORAD	Location	State	Type	From	To	GPS	Notes
P-38A		Fort Ord	CA	TPS-1D	1954	1955	36.667778, -121.818056

Current Status

Abandoned by the Air Force on Mount Tamalpais, Marin County, California.

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USGS Geographic Names Information System (GNIS) Database Entry: 2107694

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Location: On Mount Tamalpais in Marin County, California. Maps & Images Lat: 37.9239669 Long: -122.5971812 Multi Maps from ACME Maps from Bing Maps from Google Elevation: 2,431'

See Also:

• Permanent System Radar Sites
• US Radar Sets
• Beale SAGE Direction Center DC-18
• Adair SAGE Direction Center DC-13
• Luke SAGE Direction Center DC-21

Sources:

• Cornett, Lloyd H. & Johnson, Mildred W., A Handbook of Aerospace Defense Organization (1946-1980), Office of History ADC, Peterson AFB, Colorado, 31 Dec 1980, 179 pages, Pdf, page 158.
• Winkler, David F., Searching the Skies: the Legacy of the United States Cold War Defense Radar Program, USAF Hq Air Combat Command, 1997, 192 pages, Pdf, page 103.

Links:

• Radomes - Mill Valley Air Force Station
• Wikipedia - Mill Valley Air Force Station

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