Among more than two dozen major weapons systems whose designs were breached were programmes critical to US missile defences and combat aircraft and ships, the Washington Post reported citing a report by the Defence Science Board.
The electronic intrusions gave China access to advanced technology that could accelerate the development of its weapons systems and weaken the US military advantage in a future conflict, warned unnamed experts cited by the influential US daily.
Citing a confidential list of compromised weapons designs, the Post said some of the weapons form the backbone of the US defence department's regional missile defence for Asia, Europe and the Persian Gulf.
The designs included those for the advanced Patriot missile system, known as PAC-3; an army system for shooting down ballistic missiles, known as the Terminal High Altitude Area Defense, or THAAD; and the Navy's Aegis ballistic-missile defence system, it said.
Also identified in the report are vital combat aircraft and ships, including the F/A-18 fighter jet, the V-22 Osprey, the Black Hawk helicopter and the navy's new Littoral Combat Ship, which is designed to patrol waters close to shore, the Post said.
Also on the list is the most expensive weapons system ever built - the F-35 Joint Strike Fighter, which is on track to cost about $1.4 trillion. The 2007 hack of that project was reported previously.
However, the list did not describe the extent or timing of the penetrations, the Post said.
The report also listed broad technologies that have been compromised, such as drone video systems, nano-technology, tactical data links and electronic warfare systems - all areas where the US defence department and Chinese military are investing heavily, according to the Post.