It may look like it flew straight off the screen of a sci-fi movie, but the Bird of Prey is no flight of fancy - it could translate into serious business for its makers, aerospace giant Boeing.

"Here we have an example of a classic 'black' programme: an aircraft which has been built and flight tested for a number of years - and no one outside the programme knew about it," says Nick Cook, aerospace consultant to Janes Defence Weekly. Other highly classified aircraft that have ultimately been revealed included the U-2 and Blackbird spy planes and the B-2 stealth bomber.