The United States government has published drawings and schematics of a flying saucer it attempted to build in the 1950s.
The documents show that the US Air Force worked with a Candaian company, Avro Aircraft Limited, to build a craft which resembles the 'alien spacecraft' popular in movies and science fiction for more than a century.
Known as Project 1794, the aim was to create a supersonic craft shaped like a disc.
Declassified documents show that the prototype entered development in the mid-1950s, and was intended to have a top speed "between Mach 3 and Mach 4".
The craft would have flown at 100,000 feet, and had a range of about 1,000 miles.
The saucer would have also been able to take off and land vertically, use propulsion jets to stabilise itself and revolutionised air travel.
One document - a memo from 1956 - concludes "that the stablisation and control of the aircraft in the manner proposed... is feasible".
"Supersonic tests show that the calculated thrust potential with the present design will provide a much superior performance to that estimated," it adds.
The document concludes that additional tests would be needed - and that the total estimate of continuing the research would be $3,168,000 (or about $25 million accounting for inflation).
Unfortunately the project was eventually dropped. The saucers which were built under the program proved hard to fly at high altitudes and work eventually stopped in 1960.
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