Flying saucer to UFO to UAP: what each name was for

Three names, and each one was chosen to solve a problem the previous one had created. Following them is the shortest route into the history of this subject, because every rename marks a moment when somebody decided the existing word had become unusable.

Flying saucer, 1947

The phrase arrived within hours of the first famous sighting and it was a mistake almost immediately. Kenneth Arnold, describing nine objects he saw near Mount Rainier on 24 June 1947, told reporters they moved erratically, "like a saucer if you skip it across water".

He was describing the motion. The press took the noun. Within days the objects themselves were saucers, and for the rest of the century witnesses would describe discs — including many who had almost certainly seen something else.

UFO, early 1950s

By 1952 the US Air Force had a problem: "flying saucer" carried a claim in it. It asserted a shape, an object, and by implication a craft — and the Air Force wanted a term for reports it had not yet explained, without conceding any of that.

Captain Edward Ruppelt, who ran Project Blue Book, is credited with pushing "unidentified flying object". It is a deliberately empty phrase. Unidentified means only that identification failed. Flying and object are the minimum the reports assert.

The bureaucratic caution did not survive contact with the public. Within a decade UFO meant alien spacecraft in ordinary speech, which is exactly what the term had been designed to avoid, and the Air Force was back where it started.

UAP, and why twice

The British Ministry of Defence used "unidentified aerial phenomena" in its Condign study of 1997 to 2000, for the same reason Ruppelt had reached for UFO: the older term had acquired a meaning the authors did not want to assert.

The American adoption came later and went further. When the US Navy formalised reporting in 2019 and the Office of the Director of National Intelligence published its assessment in 2021, "unidentified aerial phenomena" was the term — and it was chosen in part because pilots would not file reports under a word that would get them laughed at.

The definition then widened again. "Aerial" was replaced with "anomalous" when the All-domain Anomaly Resolution Office was established, because the reports were not only aerial: some described objects entering water, and a term that excluded them by definition was no use.

Why the words matter to a reader

Because each one tells you the era a source comes from, and roughly what it assumes. A book that says flying saucer is writing in or about the 1950s. One that says UFO is post-Ruppelt and probably assumes craft. One that says UAP is post-2019 and is usually being careful.

It also tells you what a document is trying to avoid. Institutions do not rename things casually; they rename them when the old word has started making a claim on their behalf.