Ruppelt's account:

On the night of December 10, 1952, near another atomic installation, the Hanford plant in Washington, the pilot and radar observer of a patrolling F-94 spotted a light while flying at 26,000 feet. The crew called their ground control station and were told that no planes were known to be in the area. They closed on the object and saw a large, round, white "thing" with a dim reddish light coming from two "windows." They lost visual contact, but got a radar lock-on. They reported that when they attempted to close on it again it would reverse direction and dive away. Several times the plane altered course itself because collision seemed imminent.

...the "white object with two windows," we found that a skyhook balloon had been plotted at the exact site of the "battle."

Several red balls were observed in undercast weather by two experienced male military witnesses near a nuclear test site for over 15 minutes.

Project Blue Book Assessment:

I. Description of Incident

Two pilots, in an F-94 made visual and radar contact with a large, round white object larger than any known type of aircraft. A dim reddish-white light came from the object as it hovered, reversed direction almost instantaneously and then disappeared. The object appeared to be level with the intercepting F-94 at 26,000 to 27,000 feet. Airborne radar and visual contact were simultaneous and lasted for 15 minutes. F-94 attempted to contact local GCA but without success. Weather was clear above 3,000 feet. Time of sighting was 1915 PST.

II. Discussion of Incident

Two additional F-94's were in the general area but at lower altitudes and thus are eliminated as possible cause for the sighting. The description of "large, round and white and extremely large" is significant. Upper air research balloons are tear-shaped and made of translucent polyethylene and at cruising altitude expand to as much as 90 feet in length. The equipment hanging below the balloon is capable of making a return to airborne radar. Although ATIC has received no record of upper air research balloon tracks for this date the description of the object allows a preliminary evaluation of "possible balloon".

III. Conclusion: Possible balloon.

304-B. Odessa, Wash., 10 December 1952, 1915 LST. Weather: clear above undercast at 3,000 ft.; aircraft at 26,000-27,000 ft. Two pilots in an F-94 aircraft sighted a large, round white object "larger than any known type of aircraft." A dim reddish-white light seemed to come from two "windows." It appeared to be able to "reverse direction almost instantly," and did a chandelle in front of the aircraft. After this the object appeared to rush toward the aircraft head-on and then would "suddenly stop and be pulling off." The pilot banked away to avoid an apparently imminent collision, and lost visual contact. Fifteen minutes later the aircraft radar picked up something which the crew assumed was the UFO, although there is no evidence that it was. The object was reported to be moving generally from west to east at 75 knots. It was never sighted.

This sighting has been described as a mirage of Venus, although the reported 75 knot speed and 270° direction of motion is in contradiction to this hypothesis. The general description of the object as well as the reported motion is suggestive of a weather balloon. However, the peculiar reversals of direction, although they could have been illusory, and particularly the loss of visual contact are at odds with the balloon hypothesis.

The radiosonde profile for Spokane, 1900 LST, is shown in Fig.9 and is inconclusive. The tropopause, where the sharpest temperature inversions are likely, is at about 30,500 ft. above sea level, too high to have produced a mirage visible at 26,000 -27,000 ft.

The closeness of the timing between the radiosonde release at 1900 LST and the sighting at 1915 LST suggests that the F-94 crew may have seen a lighted pibal balloon. The description given, including the two dimly-lit "windows," is typical of the description of a pibal balloon by those not familiar with weather instrumentation. Such a balloon would rise to at least 17,000 ft. in 15 min., and the reported motion, 270° at 75 knots, is in excellent agreement with the upper winds at the highest level plotted for the Spokane profile: 280° at 66 knots at 18,000 ft.

Google map of this location.