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to be the "most likely or most plausible explanation." Thayer's assessment is perhaps presented more clearly by a later quotation (Condon & Gillmor, 1968, p. 174): ". . . where the observational data pointed to anomalous propagation as the probable cause of an UFO incident, the meteorological data are overwhelmingly in favour of the plausibility of the AP hypothesis." Thayer has clearly concluded that a substantial fraction of radar observations are probably due to anomalous propagation effects; but it is equally clear that he does not ascribe all radar observations to this phenomenon. The impression given by Condon's summary concerning radar-visual cases is, therefore, at variance with Thayer's summary and with the cases on which Thayer's summary is based.
Condon's account of radar cases is very similar to his account of photographic evidence: very little of what he writes makes reference to the work of his staff, and what he does write about his staff's work is misleading.
Radar Detection Without Visual Detection
Both Craig and Thayer attach special significance to Case 21 (Condon & Gillmor, 1968, pp. 310-316) [Colorado Springs, Colorado, May 13, 1967] in which clear and consistent signals were shown by two airport radars, with no corresponding visual observation. The abstract of this case [identified on Condon & Gillmor (1968 p. 3 10) only as "South Mountain (Location A), Spring, 1967"] is as follows:
Operators of two airport radars reported that a target equivalent to an aircraft had followed a commercial flight in, overtaken it, and passed it on one side, and proceeding [sic] at about 200 knots until it left the radar field. No corresponding object was visible from the control tower. On the basis of witnesses' reports and weather records, explanations based on anomalous atmospheric propagation or freak reflection from other objects appear inadequate. The case is not adequately explained despite features that suggest a reflection effect (see Section CR III, Chapter 6).
[Section CR III, Chapter 6, is devoted to "Visual Observations Made by U.S. Astronauts" and contains nothing relevant to this case.]
Craig, in his summary of "Field Studies," makes the following comment on this case (Condon & Gillmor, 1968, p. 72): "Of the current cases involving radar observations, one remained particularly puzzling after analysis of the information, since anomalous propagation and other common explanations apparently could not account for the observation. . . ."
In his summary of "Optical and Radar Analysis of Field Cases," Thayer devoted over one page (Condon & Gillmor, 1968, pp. 170-171) to this case. He remarks: "This is a radar-only case, and is of particular interest because the UFO could not be seen, when there was every indication that it should have been seen." He points out that, although no object was seen from the ground, from the landing Braniff plane, or from a following Continental Airlines plane, the UFO followed "precisely the correct procedure for an overtaking