The Air Force definitely have planes and tech that we don't know about. Google Galveston Key UFO. An oil rig worker saw a diamond shaped craft over the North Sea in the late Eighties being escorted by two planes. You also have the Calvine UFO. I believe that to have been a U.S spy plane. It was also seen later in the same month by a motorist
UFO doesn't mean its extra-terrestrial
There's an interesting documentary about a guy that worked at S4 which is an area within Area 51, it's called Area 51 and Flying Saucers. His name is Bob Lazar and he claims to have seen a number of ET craft in a hanger. He worked on one, specifically the propulsion system
He even tells you which star system it came from. He has no idea how the U.S came to be in possession of the crafts. He said one looked like it had been shot down and another was rumored to have been found in an archeological dig. I've no idea what to believe. He's either telling the truth or the world's best actor. I've watched him on Joe Rogan and he has never changed his story in thirty years
There's also a very interesting interview which can be found on you tube with a former U.S Marine called Jonathan Weygandt who whilst in South America, Peru I think, helped recover a crashed ET craft. He said it had been shot down with a surface to air missile. The level of detail he goes into is crazy. Again, if he is lying then he deserves an Oscar. If you're in to this stuff then watch it, you won't be disappointed and it will fuck with your head so be warned
Personally I don't see how we can be the only planet with life out of trillions and trillions of planets