Edward J. Ruppelt, a former Air Force UFO investigator, wrote The Report on Unidentified Flying Objects in 1956 to describe his experiences with Project Bluebook. The book gained notoriety for its hypothesis that a small number of UFO sightings might be connected to increases in atomic radiation. In his second version, published in 1960, Ruppelt claimed to be "certain" that UFOs don't exist. The Air Force has publicly said that there is no proof that an interplanetary spaceship exists ever since the first flying saucer sighting in June 1947, according to Ruppelt's argument in the foreword. What is less well known, however, is that the military and its scientific advisers are far from in agreement with this view ". When an anonymous F-86 fighter pilot fires on an unnamed target in the summer of 1952, Ruppelt tells a story about it and then mocks him for having "cracked up" or panicked. Ruppelt draws attention to the contradiction between government interest in UFOs and public denials of it at the same time that his team was actively researching it "Unnamed Air Force officials have been downplaying their interest in UFOs during this time.