Mill Valley Air Force Station

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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.

Mill Valley AFS Radome 411, Empty FPS-26A Tower
Mill Valley AFS Bachelor Airmen's Quarters, Bldg. 204
Mill Valley AFS Operations Bldg. 408 & FPS-66A Search Radome Bldg. 409


GPA-127 PPI in Operations Building 408
FPS-66A in Operations Building 408

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

Former Beale SAGE Direction Center DC-18.
Mill Valley SAGE Direction Centers & Sectors
Assigned Direction Center Sector
1 Jul 1960 - 1 Aug 1963 Beale SAGE Direction Center DC-18 San Francisco Air Defense Sector
1 Aug 1963 - 1 Apr 1966 Adair SAGE Direction Center DC-13 Portland Air Defense Sector
1 Apr 1966 - 15 Sep 1969 Adair SAGE Direction Center DC-13 26th Air Division
15 Sep 1969 - 19 Nov 1969 Luke SAGE Direction Center DC-21 27th Air Division
19 Nov 1969 - 30 Sep 1980 Luke SAGE Direction Center DC-21 26th Air Division

Common Digitizer in Operations Building 408
ATG Radios GT2122 & GRRR 232 in Operations Building 408

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

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

Mill Valley FAA Radar Site, ARSR4 Radar Tower.
Mill Valley FAA Radar Site Original JSS Site Sign.

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.

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,

Physical Plant

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.

Mill Valley AFS Structures (edit list)
Number Building Area Currently
101 Paint Locker and Lubricant Storage Cantonment No 20' x 15' Concrete Block
102 Heating Plant Cantonment Yes 35' x 30' Concrete Block
103 Civil Engineering Maintenance Shop Cantonment No 60' x 30' Frame
104 Garage and Auto Hobby Shop Cantonment No 60' x 30' Frame
105 Civil Engineering Storage Cantonment No 20' x 20' Frame
106 Bowling Alley/Radio Cantonment Yes 35' x 15' Bowling Alley
Attached to old Radio Site Building
107 Motorcycle Hobby Shop Cantonment No 30' x 25' Concrete Block
184 Pump Station and Fire Pump Storage Cantonment No
201 Bachelor Airmen Quarters Cantonment No 90' x 30' Frame
202 Administrative Building Cantonment No 50' x 20' Frame
203 Theater Cantonment No 50' x 25' Frame
204 Bachelor Airmen Quarters Cantonment No 2 Story "U" Shaped Frame
206 Post Exchange Cantonment No 75' x 20' Frame
208 Bachelor Airmen Quarters Cantonment No 2 Story 90' x 30' Frame
210 Bachelor Airmen Quarters Cantonment No 2 Story 90' x 30' Frame
212 Bachelor Airmen Quarters Cantonment No 2 Story 90' x 30' Frame
214 Bachelor Airmen Quarters Cantonment No 2 Story 90' x 30' Frame
216 Multi-purpose Cantonment No 90' x 30' Frame
218 Consolidated Open Mess (NCO Club) Cantonment No 75' x 25' Frame
220 Dining Hall Cantonment No "T" Shaped 80' x 30', 50' x 25' Frame
221 Cold storage Cantonment No
222 Supply and Administration Cantonment No 60' x 20' Frame
223 Civil Engineeering Administration Cantonment No 50' x 30' Frame
224 Physical Conditioning Center Cantonment No 40' x 30' Frame
302 Gatehouse Cantonment No Frame
304 Sewage Tank Cantonment No
305 Storage Shed Cantonment No
306 Explosive Storage Cantonment No
307 Pool Building Cantonment No Frame
400 Gatehouse Operations No Frame
402 Civil Engineering Storage/Radio Site Operations Yes 20' x 50' Reinforced Concrete
403 Training Operations No Portable
405 Supply building Operations  ?
406 Heating Plant Operations  ?
407 HF Radar Tower Operations No
408 Operations Building Operations Yes 60' x 80' Reinforced Concrete
409 Search Radar Tower Operations No 35' Diameter Steel Tower
410 Generator Building Operations No
411 FPS-26 Tower now ARSR-4 Tower Operations Yes Square Steel Tower
413 PME Lab Operations No
600-609 Base Housing Units (9) Housing No 50' x 25' Frame, 2 Small Bedrooms, 1 Bath
620 Sewer Ejector Station Housing Yes

Mill Valley AFS Major Equipment List
Search Radar HF Radar Data Systems
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)
  • Det 3, 14 MWS
666th Assignments

Mill Valley Air Force Station Partial Commanders List (edit list)
Assumed Relieved Rank Name Cullum Notes
1952~ Lt Colonel Gravette, Edgar B. N/A
1954-11 1955-02-31 Lt Colonel Trout, Kenneth E. N/A
1955-02-31 1956-06 Major Arnold, Ray E. N/A
1956-06 Major Berman, Samuel D. N/A
1957 1959 Lt Colonel Byrne, John P. N/A
1960 1961 Lt Colonel Weiser, Gus N/A
1961 1965-07-31 Lt Colonel Wright, William E. N/A
1965-08 1967-02-22 Lt Colonel Crispen, Marshall F. N/A
1967-02-22 Major Edwards, William R. N/A
1971~ Major Hiawek, Robert A. N/A

Note: Reported dates overlap and may be incorrect or reflect periods of intermittant temporary command.

Current Status

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

Location: On Mount Tamalpais in Marin County, California.

Maps & Images

Lat: 37.9239669 Long: -122.5971812

See Also:


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


Visited: 3 Sep 2017

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