Book: An Uncensored History of America's Top-Secret Military Base Book by Annie Jacobsen · 2011. Chapter 1: The Riddle of Area 51, Chapter 3: The Secret Base, and Chapter 4: The Seeds of Conspiracy
The UFO Experience. A Scientific Inquiry. J. Allen Hynek. Regnery, Chicago, Science 25 Aug 1972: Vol. 177, Issue 4050, pp. 688-689 DOI: 10.1126/science.177.4050.688
https://www.ufocasebook.com/ufohistory.html
https://www.history.com/news/historys-most-infamous-ufo-sightings
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https://time.com/5681197/area-51-raid-aftermath/