Boeing, which unveiled its hydrogen-fueled Phantom Eye unmanned aircraft in a ceremony in July, is beginning to lay out a strategic case for the larger, operational version it hopes to sell to prospective intelligence customers.

The prototype Boeing unveiled at its St. Louis factory July 12 is designed to fly continuously for four days, but the company’s real goal is a larger version that would fly for 10 days, officials said.

Three or four of the bigger planes could provide 365-day coverage anywhere over the globe, eliminating “the current need to base the aircraft in theater, thereby eliminating the need for global basing and a global supply chain,” Darryl Davis, president of Boeing Phantom Works, said during the ceremony. Boeing posted a video on its website incorporating parts of the speech.

Boeing plans to disassemble the aircraft and, by September, ship it to NASA’s Dryden Flight Research Center in California for ground and taxi tests culminating in a first flight in early 2011, said Boeing spokesman Chris Haddox. The debut flight is expected to last four to eight hours, the company said.

During the ceremony, Boeing displayed the aircraft without its two modified Ford Ranger truck engines attached, though it displayed one of the engines off to the side, Haddox said. The engines burn liquid and gas hydrogen, and Boeing is billing them as environmentally friendly.

Boeing heard about Ford’s effort to develop a cleaner burning engine about a decade ago and decided to pursue aerospace applications, Davis said in the Boeing video.

Haddox said Boeing is confident that the engines will work as planned after testing them in chamber at Aurora Flight Sciences in Manassas, Va. Aurora also builds the craft’s 150-foot long, single-piece wing.

Phantom Eye is designed to fly at 65,000 feet with a 450-pound payload and cruise at about 150 knots, Boeing said.