Side A: A colossus of engineering acumen and structural steel, the Airdock was built in 1929 as the construction facility for the U.S. Navy’s rigid airships, the USS Akron (1931) and USS Macon (1933). The airships, or dirigibles, served as the fleet’s aerial watchdogs, but with the advancement of aircraft carriers, the Navy no longer needed these leviathans of the skies, which were large enough to carry five biplanes. Eleven steel parabolic arches, cresting at 211 feet, create one of the largest open space interiors in the world and shelter more than 364,000 square feet of floor space. Only one of the arches is fixed to its concrete piling. Its 660-ton spherical doors rest on flatbed railroad cars to open. The Airdock, a National Civil Engineering Landmark, was added to the National Register of Historic Places in 1973.