Aerial Phenomena Research Organization
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The group was based in Tucson, Arizona after 1960. APRO had many state branches, it remained active until late 1988.
APRO stressed scientific field investigations, and had a large staff of consulting Ph.D. scientists. A notable example was Dr. James E. McDonald of the University of Arizona, a well-known atmospheric physicist, and perhaps the leading scientific UFO researcher of his time. Another was Dr. James Harder of the University of California, Berkeley, a civil and hydraulic engineering professor, who acted as director of research from 1969-1982. McDonald and Harder were among six scientists who testified about UFOs before the U.S. House of Representatives Committee on Science and Astronautics on July 29, 1968, when they sponsored a one-day symposium on the subject. 
Astronomer J. Allen Hynek cited APRO and NICAP as the two best civilian UFO groups of their time, consisting largely of sober, serious minded people capable of valuable contributions to the subject. 
In 1969, a sizable portion of APRO's membership elected to form a new group named the "Midwest UFO Network"; this soon expanded and became the Mutual UFO Network (MUFON), still active today.
- Clark, Jerome. UFO Encyclopedia, 2nd edition. Detroit: Omnigraphics, 1998 ISBN 0-7808-0097-4
- Saunders, D. and Harkins, R. "UFOs? Yes!". New York: Signet, 1968.
- Hynek, J. Allen, The UFO Experience: A Scientific Inquiry, Chicago: Henry Regenery Co., 1972