Boeing KC-97 refueling X-wing
On the 22nd of June 1972 major John Brown was making an unscheduled test flight with a F-106 over California. The aircraft had undergone some repairs the previous morning and the major decided to take it up for a quick test. Half an hour into the flight he spotted two large aircraft to the north flying in formation. He decided to investigate and turned north.
The aircraft turned out to be two KC-97 tankers which were refuelling two unknown aircraft. As a avid amateur photographer he had a small camera with him and making an number of passes he snapped a few pictures.
When he landed back at base he was immediately summoned to the base commander and told that he better forget what he had seen and never mention it to anybody. Feeling the seriousness of the situation he wisely did not mention the pictures he had taken.
Back home however he developed the film and printed the pictures. Not wanting to get into trouble he put the pictures in an envelope in the back of his desk drawer and forgot about them.
After his death in 2016 the pictures were found by his son who put them on the internet. They caused quite a storm but the USAF denied al knowledge of the incident and to the present day it maintains they are fakes.