An unmanned jet makes it into the history books after flying for three and and a half minutes at five times the speed of sound.

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Boeing's WaveRider prototype - part of an experimental US military project hit a top speed of nearly 4,000 miles per hour during a test flight over the Pacific last week, according to the US Air Force.

It is thought to be the longest hypersonic flight using an air-breathing engine ever.

A plane travelling at that speed could fly from London to Sydney in about two-and-a-half hours.

A video released by Boeing and the American military showed an X-51A aircraft being dropped from the wing of a bomber at around 50,000 feet.

A rocket booster propelled the plane to Mach 4.8 in about 26 seconds. The WaveRider then separated from the rocket, its scramjet engine ignited and it accelerated to Mach 5.1 at 60,000 feet.

The US Air Force said the program is aimed at paving the way to future hypersonic weapons, hypersonic intelligence, surveillance and reconnaissance missions and trips to space.

The WaveRider concept was invented by British scientist Terence Nonweiler in the 1950s and the technology was first developed as part of Britain's Blue Streak space programme.

But Britan dropped out of the space race in the 1960s and it was left to the US military to build a complete prototype.

A WaveRider is so called because its unusual shape allows it to ride on its own shockwave, improving efficiency and enabling it to fly in the hypersonic range.

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