Chinese government hackers stole crucial data from an US contractor on a top submarine development program according to the Washington Post.

Daily claims that cyberattacks sponsored by the Chinese government infiltrated U.S. Navy contractor’s computers, allowing digital thieves to access sensitive data related to secret Navy projects on a submarine anti-ship missile.

The contractor whose systems were breached has yet to be disclosed, the Washington Post reports, though “secret plans to develop a supersonic anti-ship missile for use on US submarines by 2020” was most certainly extracted during the hack, which took place over January and February 2018.

The information stolen was stored on the contractor’s unclassified network despite being “highly sensitive nature,” according to information obtained by the Washington Post.

According to the report, 614 gigabytes of material on a closely held project known as Sea Dragon were taken. Contracted for the military organization Naval Undersea Warfare Centre, Sea Dragon aims to develop a supersonic anti-ship missile for use on U.S. submarines.