Willmar Air Force Station

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Willmar Air Force Station (1956-1961) - A Cold War U.S. Air Force Radar Station. Located near Willmar, Kandiyohi County, Minnesota. Initially assigned a Permanent ID of SM-139. Closed in 1961.


Established in 1956 and became operational in 1957 as Willmar Air Force Station manned by the 721st AC&W Squadron.

Initial equipment included a variety of search radars, FPS-8, MPS-7, FPS-3 and two height-finder radars one FPS-6 and one FPS-6A.

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

Former Grand Forks SAGE Direction Center DC-11
Willmar SAGE Direction Centers & Sectors
Assigned Direction Center Sector
Apr 1959 - 1 Jun 1961 Grand Forks SAGE Direction Center DC-11 Grand Forks Air Defense Sector

The site began operation as a SAGE site in April 1959 initially feeding the Grand Forks SAGE Direction Center DC-11. On 15 Jan 1960 the squadron designation was changed from the 721st AC&W Squadron to 721st Radar Squadron (SAGE) indicating the new SAGE System role.


Willmar AFS and the 721st were deactivated on 1 Jun 1961.

Physical Plant

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

The main site housed the operations buildings, three radar towers, and the backup generators. A photograph of the main site 2 years after site closure shows two empty radome bases and a steel operations building with a SAGE annex attached to it.

The cantonment area housed the six enlisted barracks, the two bachelor officer's quarters, the orderly room, the dining hall, the motor pool and other support buildings. Most of the buildings were of the quonset hut variety.

Apart from the main site on the south shore of Foote Lake was a small 19 unit housing area for married personnel.

A single radio site appears to have been located behind the cantonment area.

Willmar AFS Major Equipment List
Search Radar HF Radar Data Systems Radio
Unit Designations
  • 721st Aircraft Control & Warning (AC&W) Squadron (1956-1960)
  • 721st Radar Squadron (SAGE) (1960-1961)
721st Assignments
  • 8 Apr 1956 - Activated at Snelling AFS, MN, assigned to 31st AD.
  • Jul 1956 - Moved to Willmar AFS, MN.
  • 1 Jan 1959 - Transferred to 29th AD.
  • Apr 1959 - Transferred to Grand Forks ADS.
  • 15 Jan 1960 - Redesignated from AC&W Sq to 721st Radar Sq (SAGE).
  • 1 Jun 1961 - Discontinued.

Current Status

Now part of Ridgewater College campus with none of the old Air Force Station buildings visible. The housing area buildings appear to be intact and in private hands.

Location: Willmar in Kandiyohi County, Minnesota.

Maps & Images

Lat: 45.1389 Long: -95.06893

  • Multi Maps from ACME
  • Maps from Bing
  • Maps from Google
  • Elevation:1,201'

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 162.
  • 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 127.
  • USGS Geographic Names Information System (GNIS) Database Entry: 2090224


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