Official documentation of UFO's began in 1948 when the US air force created project sign and later project grudge eventually becoming project blue book. During it's 18 years of activity it accumulated 12,600 sightings, with 701 being classified as 'unidentified'. For example on an evening in august 1951, several college professors sitting on a porch in Lubbock , Texas saw a roughly semicircular formation of lights sweep rapidly overhead.
After several hours the lights reappeared and appeared to be glowing blueish objects. Over the next weeks the lights were seen again and again, the air force made a thorough investigation of the Lubbock 'lights' but could never arrive at a satisfactory explanation. The lights were photographed by amateur photographer Carl Hart jr. and showed a v- shaped formation in the sky. Still unexplained.