Dr. James E. McDonald:
Many of the radar cases for which sighting details are accessible date back to 1953 and preceding years. After 1953, official policies were changed, and it is not easy to secure good information on subsequent cases in most instances. A radar case in which both ground-radar and airborne radar contact were involved occurred at about 9:40 p.m. CST on 7/29/52 (References  4, 5, 7, 10, 25). 

From the official case summary (Ref. 7) one finds that the unknown was  first detected by GCI radar at an Aircraft Control and Warning station in Michigan, and one of three F-94s doing intercept exercises nearby was vectored over towards it. It was initially coming in out of the north (Ref. 5, 25), at a speed put at over 600 mph. As the F-94 was observed on the GCI scope to approach the unknown, the latter suddenly executed a 180 degree turn, and headed back north. The F-94 was by then up to 21,000 ft, and the pilot spotted a brilliant multicolored light just as his radarman got a contact. The F-94 followed on a pursuit course for 20 minutes (Ref. 7) but could never close with the unknown as it continued on its northbound course. At the time of first radar lock on, the F-94 was 20 miles west of Pt. Huron, Mich. The GCI scope revealed the unknown to be changing speed erratically, and at one stage it was evidently moving at a speed of over 1400 mph, according to Menzel (Ref. 25), who evidently drew his information from the official files. Ruppelt (Ref. 5) states that when the jet began to run low on fuel and turned back to its base, GCI observed the unknown blip slow down, and shortly after it was lost from the GCI scope. 

Discussion. 

This case is still carried as an official Unknown. The case summary (Ref. 7) speculates briefly on whether it could have been  "a series of coincident weather phenomena affecting the radar equipment and sightings of Capella, but this is stretching probabilities too far." 

Menzel, however, asserts that the pilot did see Capella, and that the airborne and ground radar returns "Were merely phantom returns caused by weather conditions." 

No suggestion is offered as to how any given meteorological condition could jointly throw off radar at the ground and radar at 21,000 feet, no suggestion is offered to account for 180 degree course-reversal exhibited by the blip on the GCI scope just as the F-94 came near the unknown, no suggestion of how propagation anomalies could yield the impression of a blip moving systematically northward for 20 minutes (a distance of almost 100 miles, judging from reported F-94 speeds), with the F-94 return following along behind it. With such ad hoc explanations, one could explain away almost any kind of sighting, regardless of its content. I have examined the radiosonde sounding for stations near the site and time of this incident, and see nothing in them that would support Menzel's interpretations. I have queried experienced military pilots and radar personnel, and none have heard of anything like "ground returns" from atmospheric conditions with aircraft radar operated in the middle troposphere. If Menzel is not considering ground-returns, in the several cases of this type which he explains away with a few remarks about "phantom radar returns", then it is not clear what else he might be thinking of. One does have to have some solid target to get a radar return resembling that of an aircraft. Refractive anomalies of the "angel" type have very low radar cross-section and would not mislead experienced operators into confusing them with aircraft echoes. 

Source: Statement on UFO's Submitted to the House Committee on Science & Astronautics, July 29, 1968