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, later a Sage ID of Z-38 and a JSS ID of J-33. Abandoned in 1980. Site also housed Nike Missile Site SF-90DC. Now known as Mill Valley FAA Radar Site.
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 mission. The early warning mission involved tracking and identifying 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.
SAGE System Transition
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 FST-2 installation team was on site between march 1960 and Jun 1960
SAGE System Operation
The site began operation as a SAGE site in July 1960 initially under the control of 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. This was the baseline configuration as the site began SAGE operation. A FPS-26A height-finder radar replaced the FPS-6 in 1964. 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 then switched to the Luke SAGE Direction Center DC-21 where it remained until the radar site closed.
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 Air Defense Command Post SF-90DC
In September 1962, U.S. Army Air Defense Command Post SF-90DC was established to coordinate the NIKE Missle defenses for the San Francisco Area and Travis Air Force Base within the SAGE System. To support the NIKE command post Mill Valley AFS was initially equipped with the U.S. Army Battery Integration and Radar Display Equipment GSG-5 BIRDIE system, later changed out for the TSQ-51 Missile Mentor system. Using shared radar data, the command post could direct the NIKE missile defenses using target assignments from the SAGE System or, if those were not available, establish targets itself. In March of 1974, with the phase out of the Nike-Ajax and Nike-Hercules missile sites in the area, the Air Defense Command Post SF-90DC was deactivated.
Period newspaper articles and photos describe the BIRDIE system as contained in a 18' by 7' mobile computer van adjacent to the operations building and shows two consoles in the operations room in front of the plotting board.
On 1 Oct 1979 Mill Valley AFS came under TAC jurisdiction and was subsequently closed as an Air Force Station on 30 Sep 1980 when the FAA assumed operational control of the site. Now known as Mill Valley FAA Radar Site.
Mill Valley FAA Radar Site
Gap Filler Radars
Mill Valley AFS was responsible for the maintenance of one remote unattended gap-filler radar site. The unattended gap filler sites were placed in locations where the main search radar lacked coverage. These sites were equipped with short range FPS-14 or FPS-18 search radars and FST-1 Coordinate Data transmitters that sent digitized radar target data to a SAGE direction center and to the main radar site. Both the radar set and the FST-1 were dual channel to increase site up time. Maintenance teams were dispatched for regularly scheduled maintenance or when fault indicators on the FSW-1 remote monitoring equipment suggested the site had problems. The FSW-1 also allowed remote operation of specific functions such as channel changes for the radar and for the FST-1, it also allowed remote operation of the diesel generators at the gap filler site. 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.
The physical plant of the site was divided into a main operations site, a cantonment area, a housing area and a radio site. The operations main site is separated from the cantonment area by a saddle connecting the peaks. 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. Recreational facilities in the cantonment area included a theater, a bowling alley, a swimming pool, tennis courts and various hobby shops.
Apart from the main site but adjacent to the cantonment area was a small nine unit housing area for married personnel built in 1960-1961.
A separate Ground to Air Transmitter/Receiver (GATR) radio site located at Beale Air Force Base housed the radio equipment for directing aircraft intercepts. Like most early radar stations, Mill Valley originally had a radio transmitter site and a separate radio receiver site used by local controllers for voice direction of fighter interceptors to their targets. With the SAGE System, the SAGE Direction centers had the primary task of directing intercepts and the local radio sites were reconfigured, usually into a single site that was known as the Ground to Air Transmitter Receiver (GATR) site. The GATR site communicated with the interceptors from either the local site or the SAGE direction center via voice commands and/or a digital data link.
Note: Reported dates overlap and may be incorrect or reflect periods of intermittant temporary command.
Abandoned by the Air Force on Mount Tamalpais, Marin County, California.
Visited: 3 Sep 2017