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A Washington contractor, who has yet to be named, said its files on “secret plans to develop a supersonic anti-ship missile” had been hacked.

It reported its security system had been breached between January and February.

The 614 gigabyte “Sea Dragon” programme was also swiped in the attack as well.

But, it has not been disclosed what the Sea Dragon project is.

(Image: GETTY)

The Defense Advanced Research Projects Agency (DARPA) earlier this year said it had produced a similar named anti-submarine autonomous surface vessel around the time of the hack.

It remains unclear whether the two vessels are the same.

A US Navy spokesman said companies had a duty to tell the government if they had been targeted in cyber attacks.

He added: “There are measures in place that require companies to notify the government when a ‘cyber incident’ has occurred that has actual or potential adverse effects on their networks that contain controlled unclassified information.”

Tensions between Beijing and Washington have increased in recent months after US President Donald Trump threatened to slap crippling tariffs on Chinese goods.

China has also stepped up pressure on its neighbour Taiwan, prompting US nuclear bombers to swoop on the South China Sea.

The US’s intervention comes after The People’s Liberation Army-Navy confirmed its aircraft carrier strike group – led by 67,500 tone Liaoning – is now ready for war.

China’s defence ministry said the force, which contains warships and submarines, now has "combat capability”.