Along about in WW2 was when the term UFO was coined. It is simply an acronym meaning Unidentified Flying Object. During WW2 many new aircraft were rapidly being built and deployed. Many pilots did not know what they were seeing.
Standards were set for uniform reporting standards to help identify these things and the source.That was the start of the "Blue Book Project"
During Korea the F-86 was the standard fighter jet. We had flying capabilities previously undreamed of and went to altitudes thought impossible. Strange phenomena occur at high altitudes. Even during day light hours stars are visible. the planets Venus and Jupiter look like huge flying disc. After Roswell in 1947 there was speculation of Extra Terrestrials. Venus and Jupiter looked very much like some type of disk shaped flying air craft at that height. More than one pilot over Korea had tried to shoot Venus down.
There was also another phenomena, gamma radiation. At above 35,000 feet it gets to be intense, the F-86 was not properly shielded from it. When you get bombarded with Gamma, any radiation hitting your optic nerve produce a bright momentarily moving light. It seems to be large and moving at high speed.
Shortly After Korea, a pilot Col. Keyhoe wrote a very interesting book called the "Project Blue Book" some of the book is his experiences, some here say and some pure fiction. He wrote it in the format of being an official air Force report. many people believe it to be all fact.
When I entered the AF, we had been told much of this before we ever soloed.
I did see many startling things. but, since i was expecting them I knew that they were either stars, planets or Gamma effects. But, recalling those days and if I had not expected them I would have believed I saw extraterrestrial air craft.
Yes, there are specific guidelines and standard report forms for all pilots to fill out in the event they see a UFO. the reports get fewer each year as most of the sightings are no longer unknown.
I have known many pilots that have seen flying objects, but they were later identified as to what they were.
sorry, no ETs to report. Although I do believe extraterrestial life exists I doubt very much we will ever have any unannounced visitors.