UNITED NEWS INTERNATIONAL (UNI) — Chinese hackers reportedly breached computers belonging to a U.S. Navy contractor and stole a trove of highly sensitive information related to undersea warfare, including secret plans to develop a supersonic anti-ship missile.

According to a June 8 Washington Post report, hackers linked to the Chinese government stole 614 gigabytes of data from an unnamed contractor working for the Naval Undersea Warfare Center.

Among the stolen files were plans related to a secret missile project called Sea Dragon, which the Pentagon said will give its submarines a new, “disruptive offensive capability” to take on enemy ships.

Hackers also took files containing Navy signals and sensor data, cryptographic systems and the Navy submarine development unit’s electronic warfare library.

The breaches, which occurred in January and February of this year, came to light amid tense trade negotiations between the U.S. and China.