The U.S. Navy and the FBI are investigating a massive cyber breach that compromised the network of an unidentified Navy contractor, as Chinese hackers allegedly stole large amounts of data related to undersea warfare, including top-secret programs to develop supersonic anti-ship missiles for submarines by 2020, according to American officials, The Washington Post reported.

The data breach occurred earlier this year as the investigation is still ongoing. The officials said that the contractor was working at the Naval Undersea Warfare Center, a full-spectrum research, development, and testing arm of the Navy. The warfare center focuses on submarines, autonomous underwater systems, and offensive and defensive weapons systems associated with undersea warfare.

According to the WaPo, Chinese hackers stole a total of 614 gigabytes of plans for cutting-edge weapons relating to various undersea programs, as well as sensor data, submarine information about cryptographic systems, and an entire library of submarine electronic warfare data.

Since the cyber attack, this has been a nightmare for the Pentagon, as the Navy warned The Washington Post not to release further details about the secret submarine missile program, in their report. Meanwhile, Defense Secretary James Mattis ordered the Pentagon inspector general’s office Friday to investigate the massive data breach.

Bill Speaks, Director of Media Operations for the Navy said, “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.”

Speaks added that “it would be inappropriate to discuss further details at this time.”

During Admiral Philip S. Davidson nomination hearing to lead U.S. Indo-Pacific Command, he mentioned that Beijing could not develop submarine technology on their own — they had to steal it through cyberspace.

“One of the main concerns that we have,” he told the Senate Armed Services Committee, “is ­cyber and penetration of the dot-com networks, exploiting technology from our defense contractors, in some instances.”

“It’s very disturbing,” said former senator James M. Talent (R-Mo.), who is a member of the U.S.-China Economic and Security Review Commission.

“But it’s of a piece with what the Chinese have been doing. They are completely focused on getting advanced weapons technology through all kinds of means. That includes stealing secrets from our defense contractors.” Talent had no independent knowledge of the breach.

Without breaching confidentiality, The Washington Post touch on the Sea Dragon project, which was one of the programs the Chinese were able to steal in the hack.

“The Sea Dragon project is an initiative of a special Pentagon office stood up in 2012 to adapt existing U.S. military technologies to new applications. The Defense Department, citing classification levels, has released little information about Sea Dragon other than to say that it will introduce a “disruptive offensive capability” by “integrating an existing weapon system with...