It has been 65 years since the ill-fated Hindenburg burst into flames and deflated the chances that lighter-than-air ships would become anything more than a curious footnote in aviation history. Except for the limited use of the Goodyear blimp as a flying billboard, dozens of efforts to revive the glory of dirigibles have fallen flat.

But now, Pentagon officials believe that airships could play a crucial role in protecting the United States from attack. They have quietly asked the country’s largest defense contractors to develop giant unmanned craft -- two to three times as big as Goodyear’s gasbag -- that would ring the continent. Hovering high in the stratosphere, beyond the reach of unfriendly forces, such blimps would be used to spot incoming enemy missiles and planes.

The airships would be far more complicated than any built before, and it could take seven or eight years before they are deployed. But Pentagon and industry officials say technological advances, including highly efficient solar cells, make them optimistic that the giant blimps can be added to the U.S. arsenal.

“We are very excited about high-altitude airships,” Sue Payton, the Pentagon’s deputy undersecretary for advanced systems and concepts, said in a recent briefing with industry executives, according to a transcript. She added that airships have become a high-priority technology demonstration program for the Pentagon.


The effort gained momentum a couple of weeks ago when the Missile Defense Agency, charged with protecting the country from ballistic missiles, officially launched a competition to develop a high-altitude, helium-filled airship. It said such blimps should be capable of floating for months at an altitude of 70,000 feet, carrying more than 4,000 pounds of unspecified payload.

Defense contractors have until February to submit their designs, and the agency expects to award a contract in March to one or more winning firms to build a prototype airship within three years. The goal is to deploy an operational system by 2010.

Pentagon officials are cagey about how the blimps would be used and how much they would cost, but several federal agencies also want to use the airships, including the White House Office of Homeland Security, a spokesman for the missile defense agency said.

Since last year’s terrorist attacks, homeland security officials have been stepping up calls for improving surveillance of suspected terrorists.


At the recent industry briefing, Pentagon officials described one scenario in which at least 10 massive airships equipped with radar and other sensors would be used to track incoming ballistic and cruise missiles while also monitoring potential terrorist activities on the ground, according to people who attended the meeting.

The airships would rim the U.S. coastline, starting from the Puget Sound area in the Northwest, down the Pacific coast and then up the Atlantic coast to Maine. Each airship could carry 40-foot rotating radars with a footprint of about 750 miles, according to a defense industry official.

The airships, at least initially, would not carry weapons, although eventually they could be equipped with chemical lasers to shoot down ballistic missiles.

“There are some challenges to overcome, but it just looks like a concept whose time has come,” said Ron Browning, director of business development for Lockheed Martin Corp.'s Naval Electronics & Surveillance Systems unit, which has been working on a high-altitude airship for three years.


Even longtime critics of missile defense systems are intrigued by the concept.

“I don’t think that there is anything evidently preposterous about it,” said John Pike, director of GlobalSecurity.org, a think tank. “While it may feel early 20th century, it would be wrong to suggest that the airship was completely discredited by the Hindenburg, which was a different airship in almost every respect than what you are seeing now.”

Other Pentagon agencies, including the Army and the Navy, are keenly interested in the next-generation airship for tactical uses, analysts said. The helium-filled contraptions could be deployed in conflicts overseas, monitoring enemy troop movements and even carrying laser designators to provide targeting information for cruise missiles and so-called smart bombs. At 70,000 feet, they would be too high for most antiaircraft missiles.

At least 10 companies are expected to compete to build the airships, including the world’s largest aerospace companies -- Lockheed Martin, Boeing Co. and Raytheon Corp. -- as well as smaller firms such as AeroVironment Inc. The pioneering Monrovia aircraft developer built the highest-flying unmanned, solar-powered airplane.


Using airships for battle is nothing new, and in fact much of the last two centuries of developing lighter-than-air vehicles has focused on their use in surveillance and reconnaissance.

Balloons were used as aerial observation posts during the Civil War, and Germans used rigid airships to drop bombs on England during World War I. Use of airships for transportation was hurt by the 1937 Hindenburg disaster, in which the hydrogen-filled German dirigible burst into flames while landing at Lakehurst, N.J., killing 35 people on board. Since then, airships have mainly used nonexplosive helium.

For World War II history buffs, the idea of floating airships for defense is reminiscent of the hundreds of tethered blimps that hovered above London to obstruct German bombers and rockets. Locally, massive blimps regularly patrolled the coastline looking for Japanese submarines during the war. The region’s blimp heritage still is visible at the defunct Tustin Marine Air Station, where two gigantic hangars that used to house them still tower over the Orange County horizon.

And it wouldn’t be the first time that the Pentagon has looked at airships for strategic purposes. In the 1950s, the Navy built four dirigibles to hover near the Arctic Circle watching for Soviet bombers. These were retired in 1962 after satellites and stronger ground-based radar systems took hold.


Since the 1980s, the Air Force has operated 11 low-altitude aerostats -- small, tethered blimps -- around the U.S.-Mexican border, mainly to spot low-flying aircraft used by drug smugglers. But these low-tech blimps are not nearly as sophisticated as what the Pentagon now envisions.

The Pentagon’s renewed interest in airships has been driven by developments in solar power and unmanned technologies that are opening the possibility of putting blimps in the stratosphere, a long-sought goal of engineers since the Wright brothers’ first powered flight nearly a century ago.

At 70,000 feet, the aircraft would be perched above the jet stream and adverse weather. Winds are calm enough that the airships could stay in geostationary positions, hovering over a specific site for months on end. They would need to come down only to replenish their helium, which over time would leak through the airships’ skin.

At that height, sensors that have been perfected for satellites would be as much as 50 times more sensitive than if they were in space, providing highly detailed images. Radar also would be able to spot low-flying aircraft and cruise missiles that may have escaped detection by ground-based systems.


The biggest trick, perhaps, has been figuring out how to keep such airships aloft at 70,000 feet; the air at that altitude is so thin that most aircraft would have difficulty staying up. But this challenge is starting to be overcome, industry officials said. Lighter material for the skin, such as Kevlar, and other advances are bringing high- altitude airships closer to reality.

The airship envisioned by Lockheed, for one, would be controlled by four electric propellers. Lightweight solar cells could provide power to the giant blimp for months.

Analyst Pike, who first saw the military experimenting with high-altitude balloons 30 years ago, said interest in airships has climbed and fallen with the nation’s insecurities.

“Since Sept. 11, you’ve got new requirements. And every time you’ve got a novel set of requirements, the whole technology gets a new look,” Pike said, noting how the balloons he long ago witnessed led to a rash of calls about unidentified flying objects. Airships, he said, “sort of move in and out of fashion.”