Mount Lemmon Air Force Station

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Mount Lemmon Air Force Station (1956-1969) - A Cold War U.S. Air Force Radar Station first established in 1956 atop Mount Lemmon near Tucson, Pima County, Arizona. Named Mount Lemmon Air Force Station after the location. Initially assigned a Permanent ID of M-92, later a Sage ID of Z-92. Abandoned as a U.S. Air Force Station in 1969.

Mount Lemmon AFS, Former Motor Pool Site.
Mount Lemmon AFS, Former Headquarters Building Site.
Mount Lemmon AFS, Old FPS-6 Radar Tower, Observatory Domes in the Background.


Mount Lemmon AFS, Barracks Building

Established on 1 Apr 1956 and became operational in August 1956 as Mount Lemmon Air Force Station manned by the 684th 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.

Initial equipment included the MPS-7 search radar, an MPS-14 height-finder radar and for a while a TPS-10D radar set.

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.

SAGE System Operation

The site began operation as a SAGE site on 1 May 1961 initially feeding the Luke SAGE Direction Center DC-21. The search radar was upgraded to an FPS-20 and an FPS-6 height-finder radar was installed. The search radar was later updated to an FPS-67B.

Gap Fillers

Mount Lemmon AFS was responsible for the maintenance of three remote unattended gap-filler radar sites. The gap-filler sites were placed in locations where the main search radar lacked coverage. These sites sent digitized radar target data directly to a direction center. Maintenance teams were dispatched from Mount Lemmon AFS for regularly scheduled maintenance or when fault indicators suggested the site had problems. The Mount Lemmon AFS gap-filler radars were located at Sells, Benson and Globe, Arizona.

Physical Plant

The physical plant of the site was divided into the main site, a cantonment 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.

Housing for married personnel and some single personnel was provided at Davis-Monthan Air Force Base some 40 miles away. The road from Tucson to Mount Lemmon rose from 2,700' at Davis Monthan to 9,125' at the site. Transportation between Davis-Monthan and the radar site was initially by private and government vehicles but was later provided by contract buses.

A separate Ground to Air Transmitter/Receiver (GATR) radio site housed the radio equipment for directing aircraft intercepts.

Mount Lemmon AFS Major Equipment List
Search Radar HF Radar Data Systems
Unit Designations
  • 684th Aircraft Control & Warning (AC&W) Squadron (1956-1961)
  • 684th Radar Squadron (SAGE) (1961-1969)
684th Assignments
  • 1 Dec 1955 - Activated at Geiger Field, WA as 684th AC&W Squadron, assigned to the 4702nd Def Wg.
  • Jan 1954 - Moved to Kirtland AFB, NM and transferred to 34th AD.
  • Apr 1954 - Moved to Davis-Monthan AFB, AZ.
  • Spring of 1956 - Moved to Mt. Lemmon AFS, Tucson, AZ.
  • 1 Jan 1960 - Transferred to LA ADS.
  • 1 May 1961 - Transferred to Phoenix ADS.
  • 15 Oct 1961 - Redesignated from 684th AC&W Sq to 684th Radar Sq (SAGE).
  • 1 Apr 1966 - Transferred to 27th AD.
  • 31 Dec 1969 - Inactivated.

Mount Lemmon AFS Gap Filler Radar Sites (edit list)
ADC NORAD Location State Type From To GPS Notes
M-92A Z-92A Sells AZ FPS-14, FST-1 unk unk 32.11222,
M-92C Z-92C Benson AZ FPS-14, FST-1 unk unk 31.98333,
M-92D Z-92D Globe AZ FPS-14, FST-1 unk unk 33.66,

Mount Lemmon Air Force Station Partial Commanders List (edit list)
Assumed Relieved Rank Name Cullum Notes
1954-06~ 1956-03~ Captain Chesnutt, Guy C. N/A First Commander?
1956-03~ 1956-07 Lt Colonel Catlin, James E. N/A
1956-07 Captain Weems, Raymond N/A
1956-09 1958-06-05 Lt Colonel Smith, Robert C. N/A
1958-06-05 1959-09-25 Major Agee, Charles N/A
1959-09-25 1960-09-02 Lt Colonel Burris, John F. N/A
1960-09-02 1962 Lt Colonel Hanson, Marshall E. N/A
1963-08 Lt Colonel Morrison, Ernest B. N/A
1963-08 1964~ Lt Colonel Sanders, Edward A. N/A
1966~ Major Evans, E.E. N/A
1969~ 1969-12-31 1st Lt Moore, Timothy N/A Last Commander

Current Status

Mount Lemmon Observatory Entrance Sign

Repurposed as Steward Observatory, Mt. Lemmon Station, University of Arizona, Pima County, Arizona. Some of the original site buildings have been repurposed, some have been destroyed and at least one moved and reused at a lower level visitor center. One of the radar towers remains but with a smaller radar bubble attached.

Location: On Mount Lemmon near Tucson in Pima County, Arizona.

Maps & Images

Lat: 32.44167 Long: -110.78944

  • Multi Maps from ACME
  • Maps from Bing
  • Maps from Google
  • Elevation: 9,114'

GPS Locations:

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 160.
  • 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 99.
  • USGS Geographic Names Information System (GNIS) Database Entry: 2089732


Fortification ID:

  • AZ0162 - Mount Lemmon Air Force Station

Visited: 15 Mar 2015

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