It's neither a bird nor a plane taking to the skies over the Florida Straits, it's an "eye in the sky," according to George Spyrou.

The chief executive officer of Greenwich-based Airship Management Services Inc. said last week that his company's blimps have taken on a new role with the Department of Homeland Security.

AMS, along with the U.S. Navy and Coast Guard, is testing "long-duration surveillance" aboard a specially equipped Skyship 600 craft, which the Greenwich company manufactures in North Carolina.

"It's an old use," Spyrou said Friday. "It's back to the future in a way. That's what airships were supposed to be."

AMS's airships have a lot of uses, including as sightseeing vessels, camera platforms for sporting events and providing silent security over high-profile places and events, such as the 2004 Athens Olympics.

According to the Coast Guard, its studies have shown the potential for airships to provide maritime surveillance. The patrols off the Florida coast will evaluate how effective blimps can be in spotting possible immigration violators, narcotics runners and other smugglers.

A Westport aviation consultant agrees that airships may be well-suited to the homeland security mission.

"For border patrol and things, they're wonderful," said John Pincavage, president of Pincavage & Associates. Among other virtues, airships use very little fuel, can remain on station for extended periods and carry specialized surveillance gear, Pincavage said.

However, he added, they get blown around by strong winds and have to be removed from harm's way before storms. Blimps are also too slow and too big of a target to engage anything that might shoot back, Pincavage said.

But Spyrou noted that the commanding presence of an airship can be a deterrent to the bad guys.

"In World War II they were using airships to escort convoys," he said. Online encyclopedia Wikipedia, citing J. Gordon Vaeth's "Blimps & U-Boats," published by the U.S. Naval Institute Press, says that only one of about 89,000 ships escorted by blimps off the coast of the U.S. during the war was sunk by an enemy submarine, compared to 532 unescorted ships that were lost.

The AMS Airship has been equipped with a Furuno radar system to detect surface vessels, as well as other equipment that gives its technicians the ability to scan the sea day and night, Spyrou said.

That equipment, as well as the stamina of crews flying eight-hour patrols, will be key to seeing whether the airship can be a replacement for - or enhancement of - the fixed-wing aircraft and helicopters now in use.

"We can't go as fast, but we can enhance their capability as an eye in the sky, to allow them to conserve their resources and deploy when necessary," Spyrou said.