Scientists piece together a US Navy zeppelin's past

An 18-inch piece of metal wasn't exactly what commercial fisherman David Canepa and his two-man crew expected to see when they hauled in their sablefish traps during a five-day cruise off California's Point Sur 27 years ago.

They weren't sure what it signified, but they figured their catch of corroded aluminum might be from some sort of aircraft, he recalls. "By looking at the piece and its structure, we knew it wasn't any kind of ship or boat."

During the past 17 years, marine archaeologists have followed that clue from its display on a restaurant wall to Mr. Canepa's meticulous ship logs to the ocean bottom. Last week, researchers completed the first exhaustive survey of the metal chunk's source – the Navy dirigible USS Macon and its small complement of fighter aircraft. Launched in April 1933, the dirigible and four of its planes went down in a storm off Point Sur in February 1935. All but two of its 100-man crew survived. The USS Macon's loss marked the end of one of the most colorful periods in US aviation history.

The survey is the third visit to the wreck since researchers first reached it in 1990. The results will help federal and state agencies, including the US Navy, devise a management strategy for the sea-floor site. It lies under more than 1,500 feet of water within the boundaries of the Monterey Bay National Marine Sanctuary.

The USS Macon was one of four zeppelins the Navy flew in the 1920s and '30s. It measured 785 feet from nose to tail and was a flying aircraft carrier designed for reconnaissance work over the Pacific Ocean. It drew its lift from 12 helium-filled bladders and its thrust from eight 12-cylinder engines along its flanks. Five gnatlike biplanes, armed with machine guns and lowered through the bottom of the hull on a trapeze, called its cavernous interior home.

The wreck may be the best preserved – and perhaps only – example left from the heyday of dirigibles, notes Bruce Terrell, a senior archaeologist with the National Oceanic and Atmospheric Administration's National Marine Sanctuary Program. The US's first zeppelin, the German-built USS Los Angeles, was scrapped in 1939. The USS Shenandoah crashed in Ohio in 1925. And the Macon's sister ship, the USS Akron, crashed in the Atlantic shortly before the USS Macon took her first flight. But currents and fishing trawlers have scattered the Akron's remains. "There isn't much left of it," Mr. Terrell says.

During a five-day cruise in mid-September aboard the Monterey Bay Aquarium Research Institute's R/V Western Flyer, the research team used a tethered, remotely operated vehicle (ROV) equipped with high-definition TV cameras to scan the site.

As crew members aboard the ship guided the vehicle back and forth along the bottom of the wreck's two debris fields, the hanger bay and four of the "Sparrowhawk" fighter planes slid into view. The team found five of the eight engines, as well as artifacts from the galley, the bow section and its mooring mechanism, as well as chairs and desks that may have tumbled out of officers' cabins.

Some of the large-scale objects first appeared in images taken in 1990 and 1991. Last year, researchers returned to the site and used side-scan sonar to map it. But on this trip, photos are rendered in far greater detail than was the case on the earlier photo expedition.

For example, the four fighters are in relatively good condition; Some still have fabric covering the wings. Each plane wore a unique color and stripes on the upper wing and fuselage. Chris Grech, one of the lead investigators on the cruise and a member of the team that visited the wreck in the early '90s, notes that the new camera gear enabled this year's group to tease out these faint markings on two of the aircraft. Earlier images failed to reveal the markings.

On a personal note, adds Terrell, the finds are enabling researchers to help relatives of the crew connect with their family history. The son of the USS Macon's squadron commander, a friend of Terrell's, is hunting for his father's flight logs to see if one of the crafts the expedition identified is his father's plane.

Ultimately, the team will build a mosaic from individual "screen-grab" images that cover both debris fields. This will let them build a catalog of artifacts at the site. "Because it's high definition and on computers, we'll be able to zero in on minute little artifacts that we couldn't pick out while we were using the ROV in real time," Terrell says.

In addition, researchers will use the montage to view the site from a distance, allowing them to pick out patterns not visible within the 30-foot range of the ROV's lights and camera. The team already has assembled a rough mosaic, Terrell says, and it shows enormous girder rings under a layer of mud. These rings shaped the 133-foot-diameter hull.

From a preservation standpoint, the wreck lies in a unique location. The remains, which belong to the Navy, also are protected by state and federal regulations. But if the wreck remains relatively safe from human encroachment, it's still vulnerable to tide and turbulence. Currents are slowly spreading the debris. Over the past 15 years, pieces of wreckage have been covered by a two- to three-inch layer of mud. Worm holes are visible in wooden artifacts.

The USS Macon "may end up being completely buried in another 15 years," Terrell says. Thus, this survey and what it says about the rate of the site's decline is likely to inform decisions on whether to try to recover any of the artifacts before the USS Macon meets the USS Akron's archaeological end.