(Newser) – Chinese government hackers broke into the unclassified computer network of a Navy contractor in January and February and accessed 614 gigabytes of technological information about a submarine-based missile known as Sea Dragon, as well other highly sensitive classified data, reports the Washington Post. Sea Dragon is a $300 million project scheduled for underwater testing in September. In recent years, the Pentagon has ramped up investment in technologies capable of sinking enemy ships in response to a resurgence in China's and Russia’s forces at sea. The Chinese have hacked US military information before. They obtained plans for, among others, the patriot PAC-3 missile system, the F-35 joint strike fighter, and a system for shooting down ballistic missiles, according to the Post.

The theft has raised questions about the Navy’s handling of contractors, particularly those working on high-tech weapons. The US protects its secrets using “highly compartmented security systems,” says retired admiral James Stavridis. When one of those is hacked, “you give up an enormous advantage in surprise.” The report comes at a tricky time in US-China relations. The White House is seeking Beijing’s help in negotiating with North Korea over its nuclear weapons, while at the same time sparring with China over trade and China’s territorial claims in the South China Sea, reports the Hill. (Read more submarine stories.)

