July 18, 1957 — Mount Lemmon AFS, Arizona
10:46 p.m. Capt. Claiborne F. Bickham and a radar crew at Mount Lemmon Air Force Station [now closed] northeast of Tucson, Arizona, using both MPS-7 L-band search and MPS-14 S-band height-finder radars, track a stationary target at 42,000 feet to the northwest about 82 miles away south of Chandler. The target responds to encrypted military IFF Mode 3 transponder signals and transmits encrypted responses that result in “normal Mode 3 paint” on radar scopes. A very slight strobe comes from the object that appears like Electronic Counter Measures jamming. [Eberhart]
Record Card:
Disposition: [insuff. data, likely balloon]
Telex:
Sources:
Jerome Clark, The UFO Encyclopedia, 3rd Ed., p. 997;
Jerome Clark, The UFO Encyclopedia, 4th Ed., p. 1110;
Brad Sparks, Blue Book Unknowns Catalogue, Case 1239, p. 245; [One of Sparks ‘Unknowns’, BB did not seem to consider it an unknown]
Robert Powell, UFOs: A Scientist Explains What We Know (And Don’t Know), 2024, p. 92;
NICAP, “Ground Radar Track Responds to IFF Mode 3”;