Back in world war 2 they claim flying saucers were flying around the USS Roosevelt while at sea as it was the first nuclear powered aircraft carrier and that many of the crew saw the UFO's. I don't know, I'd believe it when I saw one.
depends what you mean by aliens, if you mean what the movies show us then no definetly not. But i'm sure theirs other creatures out their similar to animals probably not as intelligent as humans though, and definetly not creatures that can build super fast flying machines hmph and tease humans by flying them around remote areas every once in a while