1947.06.25 – 1947.07.16
Hundreds of reports of sightings of similar objects followed [the Arnold incident]. Many of these came from highly credible military and civilian sources. These reports resulted in independent efforts by several different elements of the military to ascertain the nature and purpose of these objects in the interests of national defense. A number of witnesses were interviewed and there were several unsuccessful attempts to utilise aircraft in efforts to pursue reported discs in flight. Public reaction bordered on near hysteria at times.
In spite of these efforts, little of substance was learned about the objects until a local rancher reported that one had crashed in a remote region of New Mexico located approximately seventy-five miles northwest of Roswell Army Air Base…
(Eisenhower Briefing p 003)
Within a week of Kenneth Arnold’s sighting there was furious military activity. We can piece together what went on from hundreds of documents released decades later under the US Freedom of Information (FOI) Act and from interviews with some of those who were involved at the time…
There were 850 sightings reported between June and July.
(The Complete Book of UFOs, Hough and Randles)
And then it was 1947, with its striking wave of unknown discs which flew over the United States from the end of June to mid-July…
Press coverage of the [Kenneth Arnold] incident triggered a veritable wave of observations during the following months, more than 850 sightings being reported in June – July alone, the wave reaching its crest between 25 June – 16 July.
(UFOs 1947-1987: The 40-Year Search for an Explanation, Evans and Spencer)
A study by Bloecher of North American reports over the four-week period bracketing the Arnold sighting lists 853 events, including 38 sightings made before Arnold’s heavily publicized sighting.
(Report on the UFO Wave of 1947, Bloecher)
(UFOs: What to Do? {RAND Corporation document}, Kocher)
By 16 July the US Army Air Forces had received over 850 reports.