Yaak Air Force Station radar-visual sightings

Yaak Air Force Station sat on Hensley Hill in Lincoln County, Montana, on what Edward J. Ruppelt called "the extreme northern border of the United States." It was home to the 680th Aircraft Control and Warning Squadron of Air Defense Command, a Ground-Controlled Intercept and warning station. Its AN/FPS-3 search radar and AN/FPS-4 height-finder had only become operational in April 1952. That summer, the United States was in the middle of a wave of sightings. In July, radar and visual reports had come in over Washington DC.

Monday, 1 September 1952. Labor Day, about 4:45 a.m. An airman first class at the 680th took a call from Sheepman, the 760th AC&W Squadron at Colville, Washington. The call concerned "a strange light in the sky, southeast from our station." His name survives only uncertainly, as Leonard Oberlierf, Oberierf or Obering.

Two enlisted men watched the sky. Three men watched the AN/FPS-3. The Blue Book summary is spare. "Two small, varicolored lights became black silhouettes at dawn; flew erratically. One hour."

Ruppelt told it his own way. The radar crew saw a "dark, cigar-shaped object" right where the radar had the UFO pinpointed. He compared it to the Brookley AFB sighting. Except this one ended in daylight.

The day was not over. At 8:23 p.m., according to Brad Sparks's catalogue and the historian Loren E. Gross, six blips appeared on the FPS-3 scopes at once. The targets changed direction "as many as five times a minute." Some turns were 90 degrees. Measured speeds ran from 1,400 to 1,600 mph. They came within 10 miles of the site. "So close was the indicated range that radar personnel left their windowless operations room to check the sky." Outside, they saw six objects about 10 miles away.

On the scope, the formation kept changing. First in-trail. Then in-line abreast. Finally, a vertical stack. S/Sgt. William Kelly later remembered tracking "vertical climbs that exceed the limit of the site's height-finding equipment."

Project Blue Book filed the dawn episode as unidentified. It later appeared in Don Berliner's list of Blue Book unknowns, compiled from Air Force files he reviewed at Maxwell AFB in 1974. Capt. Roy James, the project's radar specialist, reportedly "tended to dismiss the incident as some sort of atmospheric trick."

Ruppelt considered radar-visual cases the most convincing in the files. Of Yaak, he wrote: "What these people saw is a mystery to this day." The evening episode is catalogued as case 808 by Brad Sparks. No separate official evaluation of it has been found.

Ruppelt dated his story to August 1. Blue Book holds no Yaak case for that day, but does for 1 September, and Gross treats them as one event. Ruppelt describes one object. The Blue Book summary describes two. The evening sighting rests on later sources and on Kelly's recollection. Sceptics point to anomalous propagation, the kind of atmospheric trick Capt. James suspected.

No photographs or film are known to exist. What remains is a Blue Book file, a handful of quotations, and a radar crew who stepped outside to look. The case lives on in Ruppelt's book, in Richard Hall's The UFO Evidence, in Gross's history and in Sparks's catalogue of Blue Book unknowns.