# July 18, 1957 — Mount Lemmon AFS, Arizona — Ground Radar Track Responds to IFF Mode 3

**URL:** https://uapdiscovery.discourse.group/t/july-18-1957-mount-lemmon-afs-arizona-ground-radar-track-responds-to-iff-mode-3/259
**Category:** Blue Book Unknowns
**Created:** [July 17, 2025, 11:13pm UTC](https://uapdiscovery.discourse.group/t/july-18-1957-mount-lemmon-afs-arizona-ground-radar-track-responds-to-iff-mode-3/259 "2025-07-17T23:13:35Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![jeffknox](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@jeffknox](https://uapdiscovery.discourse.group/u/jeffknox)
#### Post date: [July 17, 2025, 11:13pm UTC](https://uapdiscovery.discourse.group/t/july-18-1957-mount-lemmon-afs-arizona-ground-radar-track-responds-to-iff-mode-3/259/1 "2025-07-17T23:13:35Z")

</div>

![53e300642dc54.image](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/7/7712c0c98d0127d8c28b03b24b4bdda4a59e54fa.jpeg)

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:

 ![07181957-MtLemmonAZ-BBCard](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/7/79ebd7d5bde68392b2392da8972508ef2c496261.jpeg)

Disposition: [insuff. data, likely balloon]

 ![07181957-MtLemmonAZ-BB-1](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/3/3eca8401e5516de9145e04bd2d084f28ac1d4324.jpeg)  
 ![07181957-MtLemmonAZ-BB-2](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/b/b96197c545be7727d82c5937fd62acc54465258f.jpeg)

Telex:

 ![07181957-MtLemmonAZ-BBTelex-1](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/e/e66cfddcb0ad6871e5be697514fb094ad7222752.jpeg)  
 ![07181957-MtLemmonAZ-BBTelex-2](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/f/f123cb667532574da5c71b70efbecee23fec8a2a.jpeg)  
 ![07181957-MtLemmonAZ-BBTelex-3](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/c/ccfe9f7a2b028a29519f1ea98c018d2459e42923.jpeg)

Sources:  
Jerome Clark, The UFO Encyclopedia, 3rd Ed., p. 997;  
Jerome Clark, The UFO Encyclopedia, 4th Ed., p. 1110;

 ![07181957-MtLemmonAZ-ClarkIII-p997](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/8/8081ec9cbda24267fda7771aa61020eafafbb42f.png)

Brad Sparks, Blue Book Unknowns Catalogue, Case 1239, p. 245; [One of Sparks ‘Unknowns’, BB did not seem to consider it an unknown]

 ![07181957-MtLemmonAZ-Sparks-Case1239-p245](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/d/df005bd0c1e359f6b2e7905b738065676070361d.png)

Robert Powell, UFOs: A Scientist Explains What We Know (And Don’t Know), 2024, p. 92;

> **[UFOs: A Scientist Explains What We Know (And Don’t Know): Powell, Robert:...](https://www.amazon.com/UFOs-Scientist-Explains-What-Know/dp/1538173581)**
>
> UFOs: A Scientist Explains What We Know (And Don’t Know) \[Powell, Robert\] on Amazon.com. \*FREE\* shipping on qualifying offers. UFOs: A Scientist Explains What We Know (And Don’t Know)

 ![07181957-MtLemmonAZ-PowellScientist-p92](https://canada1.discourse-cdn.com/flex011/uploads/uapdiscovery/original/2X/b/bc1f62b146bf1745942eaccdb0a99f7c582e0f31.jpeg)

NICAP, “Ground Radar Track Responds to IFF Mode 3”;

> **[UFO Report](http://www.nicap.org/570718MtLemmon_dir.htm)**