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.