Armed with declassified documents and vivid details, a group of former Air Force officers gathered Monday to go public with an assertion they have kept mostly under wraps for decades: that UFOs visited the bases they were stationed at and caused nuclear weapon system to temporarily malfunction. The group, convened by UFO researcher Robert Hastings, came to the National Press Club in Washington to discuss their individual experiences and to urge a government that tried to ignore and silence them when they came forward years ago to finally come clean. Hastings said he believes that visitors from outer space are fixating on nuclear weapons because they want to send a message: Disarm before the world destroys itself. Hastings said he has heard of a UFO incident occurring at Malmstrom as recently as 2007. The declassified documents Hastings presented at Monday's news conference include decades-old government memos detailing reports of sightings of objects in the skies above Alabama, Montana, New Mexico and North Dakota. He has talked to 120 former or retired U.S. military about the presence of UFOs at nuclear weapons sites across the United States and around the globe as early as 1945, when the world entered the nuclear age with the bombings of Hiroshima and Nagasaki. For some of the officers who came forward Monday, going public wasn't easy. Bruce Fenstermacher, a missile combat crew commander at F.E. Warren Air Force Base in Cheyenne, Wyo., was laughed at" by superiors when he reported a UFO sighting at a launch site that one of his sergeants had passed on to him, he said. He decided to keep his head low after that. "I was very careful about who I told what," he said. "I was concerned. I don't want to be considered a kook. But I think it's more important to come out and tell our story."