Chinese government hackers stole a ton of American submarine warfare secrets from a Navy contractor, U.S. officials revealed, according to a new report on security breaches.

China infiltrated a contractor affiliated with the Naval Undersea Warfare Center earlier in 2018 and stole massive amounts of data on highly-sensitive projects, including a secret supersonic anti-ship missile for U.S. submarines, officials told The Washington Post. The Chinese also made off with the Navy submarine development unit’s electronic warfare library, among other materials.

The Ministry of State Security, the civilian spy agency believed to have carried out the notorious Office of Personnel Management hack, is suspected to have been behind the intrusion into U.S. systems.

Chinese hackers have long threatened America’s military secrets.

A Chinese businessman pleaded guilty in March 2016 to conspiracy to hack the vulnerable computer networks of U.S. defense contractors between 2008 and 2014. He is believed to have facilitated the theft of important information on the F-35 Lightning II Joint Strike Fighter, as well as other U.S. military planes, during a serious breach around 2009. China developed the J-20 stealth fighter just a few years after the breach.

The Chinese fifth-generation fighter looks like a cross between the F-35 and the F-22, and many suspect that espionage played a role in the development process. (RELATED: China Plans To Unveil Stolen US Fighter Jet In Big Show)

Beijing argued that the Chinese businessman allegedly involved in the plot was not a Chinese spy, but a nationalist Chinese media outlet with ties to the state said that the Chinese people should “show our gratitude and respect for his service to our country.”

“On the secret battlefield without gunpowder, China needs special agents to gather secrets from the U.S.,” the report from China’s Global Times wrote in after the man was sentenced.

There is evidence China snatched designs for American ballistic missile defense systems, such as the PAC-3 and THAAD systems, and China is also believed to have incorporated stolen drone technology into its new designs.

For two years, a cyber-espionage unit in Shanghai targeted around 20 foreign defense contractors, the New York Times reported in 2013. The purpose of the operations, according to American cybersecurity firm FireEye, was to acquire the technology behind America’s drone dominance. China has also managed to reverse engineer U.S. technology obtained from third parties.

China’s CH-4 and CH-5 unmanned aerial vehicles bear a strong resemblance to America’s MQ-9 Reaper drone. (RELATED: China Swears It Will One-Up US Drone Technology With Stolen US Drone Technology)

Beijing denies any involvement in espionage, but evidence suggests that China has been targeting defense contractors to erode America’s advantage. The U.S. has the edge at sea, but China is eager to build up its naval capabilities. America’s submarine warfare capabilities will be key to combating China’s military rise, which might explain the alleged theft.

The Navy, with the assistance of the FBI, is investigating the breach. “We treat the broader issue of cyber intrusion against our contractors very seriously,” a Navy spokesman said in response to the latest incident.

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