The FBI is investigating after the Chinese government hacked a US Navy contractor and stole highly sensitive security data, US media say.
Data stolen in the breach include plans for a supersonic missile project, US officials told the Washington Post.
The attacks, in January and February this year, were confirmed by CBS News.
Hackers targeted a contractor linked to a US military organisation that conducts research and development for submarines and underwater weaponry.
Speaking on condition of anonymity, US officials told the Washington Post the firm had been working for the Naval Undersea Warfare Center, a military organisation based in Newport, Rhode Island.
They added that among the material accessed were data relating to a project known as Sea Dragon, as well as information held within the navy submarine development unit’s electronic warfare library.