A new report concedes that much about the observed phenomena remains difficult to explain, including their acceleration, as well as ability to change direction and submerge. he report determines that a vast majority of more than 120 incidents over the past two decades did not originate from any American military or other advanced U.S. government technology, the officials said. That determination would appear to eliminate the possibility that Navy pilots who reported seeing unexplained aircraft might have encountered programs the government meant to keep secret.