TOP secret documents have reportedly revealed that Chinese spies stole key design information about Australia’s new Joint Strike Fighter, the F-35 Lighting II.

The documents, which were disclosed by former US National Security Agency intelligence contractor Edward Snowden to German magazine Der Spiegel, show that Chinese cyber spies stole “huge volumes” of sensitive military information relating to the plane.

The stolen information includes details of the fighter’s radar systems, engine schematics, methods for cooling exhaust gas and “aft deck heating contour maps”, Fairfax Media reports.

The Snowden documents reportedly confirm the Australian government has been informed of the cyber-espionage.

The Snowden documents appear to be the first public confirmation of the long-held suspicion that the F-35 has been the target of Chinese cyber-espionage.

As reported last week, China’s new fifth-generation fighters, including its first attempt at a stealth fighter — the Chengdu J-20 — have significantly eroded the West’s superiority in the skies.

Experts have speculated that the Chengdu J-20 and China’s most advanced fighter jet, the Shenyang J-31 Falcon Hawk, have been heavily influenced by US design.

The Falcon Hawk has roughly the same appearance as the F-35.

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Fairfax reports the data breach occurred at the main contractor Lockheed Martin in 2007, which predates Australia’s acquisition of the aircraft.

In June 2013, Defense Department acquisitions chief Frank Kendall told a US Senate hearing that he was “reasonably confident” classified information related to the development of the F-35 was protected.

Prime Minister Tony Abbott announced in April last year that Australia would buy 58 F-35 jets for $12 billion, bringing Australia’s total JSF fleet to 72. The

The Snowden documents show that Chinese cyber-spies stole the equivalent of five Libraries of Congress, amounting to 50 terabytes of data.

Among the sensitive military technologies included in the breach was information about the B-2 stealth bomber, the F-22 Raptor stealth fighter, nuclear submarine and military personnel records.

The documents also show that the US National Security Agency (NSA) spied on China’s espionage agencies. The NSA hacked the computer of a senior Chinese military official and stole information about Chinese intelligence targets in the US government and other foreign governments.