The US Navy really wants a flying stealth drone. To that end the organisation has been developing a number of prototypes, the most prominent of which is the 'UFO' styled X-47B combat demonstrator.
While looking similar to other UAV drones, the Navy definitely has the claim of it being not only the most capable, but the scariest.
Whereas others have been limited to flying over land, the X-47B is capable of taking off/landing on a carrier, performing a range of defence and strike duties and -- most recently -- can even refuel itself using an airborne tanker.
Depending on which way you look at it however, there's some good/bad news. The X-47B is already a relic, the drone has carried out all the tests that were asked of it and it'll be sent to a museum to scare small children and mildly concern adults.
The Navy plans to use the results from this two year experiment to shape the designs for their next prototype and eventually, their first unmanned naval fighter jet.