A massive unmanned spy plane being developed by Boeing completed its sixth test flight in mid-December, setting a new prototype endurance record by flying for more than five hours, company officials said.

Boeing's colossal Phantom Eye is a liquid hydrogen-powered drone designed for long-lasting intelligence and reconnaissance missions at high altitudes. While the December test flight, from Edwards Air Force Base in California, surpassed five hours, the Phantom Eye is designed to eventually be able to fly for up to four days at 65,000 feet (19,800 meters), according to Boeing officials.

The bulbous drone has a wingspan that stretches 150 feet (46 meters), and can carry up to 450 pounds (204 kilograms). The unmanned aircraft can be outfitted with various intelligence-gathering instruments, including sensors to monitor and track communications.

The drone flew its first test flight on June 1, 2012, remaining aloft for 28 minutes and reaching an altitude of 4,080 feet (1,244 meters). But, the inaugural outing ended with a rough touchdown, causing one of the landing gears to break.

Engineers subsequently performed repairs and upgrades, and the Phantom Eye flew again on Feb. 25, 2013, remaining in the air for 66 minutes and reaching an altitude of over 8,000 feet (2,440 meters).

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