evidence: One of the places the balloon was spotted was over the state of Montana, which is home to one of America's three nuclear missile silo fields at Malmstrom Air Force Base. The official spoke on condition of anonymity to discuss sensitive information. [...] The defense official said the spy balloon was trying to fly over the Montana missile fields, but the U.S. has assessed that it has "limited" value in terms of providing intelligence it couldn't obtain by other technologies, such as spy satellites. [...] The surveillance balloon was first reported by NBC News.