By: Megan Lickliter-Mundon, Co-Principal Investigator of USS Macon Survey, NOAA
Editor’s Note: Lickliter-Mundon is a graduate student attending Texas A&M University’s Nautical Archeology Program. As part of her program studies, she initiated the coordinated efforts between the Naval History and Heritage Command (NHHC) and National Oceanic and Atmospheric Administration in the Macon survey, acting as the co-principle investigator. NHHC, as managers of U.S. Navy sunken military craft, also served as one of the co-principal investigators for the project.
USS Macon (ZRS 5), a U.S. Navy Akron-class rigid airship, sank on February 12, 1935 off the coast of California in what is now the Monterey Bay National Marine Sanctuary. USS Macon’s wreck site contains some of the oldest known aviation material submerged in saltwater. Archaeologists from Naval History and Heritage Command’s Underwater Archaeology Branch (UA) helped lead a joint-organizational project with archaeologists from National Oceanic and Atmospheric Administration’s (NOAA) Office of Marine Sanctuaries and Ocean Exploration Trust (OET) to conduct an archaeological survey of the Macon wreck site in August 2015. The metal and organic remains of the airship and its four associated Sparrowhawk biplanes appear to retain a high level of preservation. The project’s goals were to update existing site documentation by producing a 2D photomosaic and 3D model of the site, and to recover and conserve a sample of airship frame to continue a catalogue of site deterioration. These studies will increase our general archaeological knowledge of the potential longevity of aviation sites in deep water.
Following the mapping portion of the survey the remotely operated underwater vehicle (ROV) Hercules was able to pick up a piece of the airship frame which was partially buried near one of the biplanes. The frame was stowed inside of Hercules’ onboard sample containers, lifted to the surface, kept wet and prepared for transfer to NHHC’s UA Archaeology & Conservation Laboratory for stabilization and treatment.
The frame arrived at UA’s Archaeology & Conservation Laboratory a few days after the survey ended where it was placed directly into a solution of citric acid and sodium hydroxide. Macon’s frames were constructed using a type of aluminum alloy called duralumin, utilized in early aircraft because of its strength and light weight. Aluminum alloys typically form a natural passive oxidation layer which helps protect the metal surface from corrosion. The citric acid-sodium hydroxide bath allowed conservators to remove this oxidation layer in a controlled manner and extract corrosion-causing salt compounds deposited by the sea water inside tiny pits on the metal surface. The chemical baths also helped remove harder concretions on the artifact surface and returned a bright luster to the metal which had been dulled to a deep gray over time. Finally, conservators slowly dried the frame and coated the surface with a special type of wax to help protect against corrosion.
Throughout the treatment process, conservators seized on the rare opportunity to study the frame and the effects of the underwater environment on its preservation. Understanding the preservation of small components like the frame may help researchers predict decay processes, areas of stress and structural instability on the entire Macon site. For example, conservators observed that the part of the frame that was exposed in the water column was in slightly better condition than the part that was buried in sediment. Conservators also discovered two rivets still in place along the side of the frame where most other riveted areas had deteriorated considerably. Elemental analysis of the rivets showed a higher iron concentration than in other areas on the artifact which indicates that an interaction between iron and aluminum may have occurred at these specific locations likely accelerating deterioration and preferentially decaying the purer aluminum components around the rivets.
Now that the frame is treated and stable, it is being curated at the UA Archaeology & Conservation Laboratory at NHHC headquarters on the Washington Navy Yard with eventual plans to place it on display in a museum.
Click here to learn more about NHHC’s Underwater Archaeology Branch’s 20 years of history. In 1996, underwater archaeology was officially incorporated into the U.S. Navy. The development of NHHC’s (UAB) was influenced by a long list of prominent archaeological projects and a number of emergent issues that were, and still are, unique to Navy ship and aircraft wrecks. While the Navy’s ship and aircraft wrecks contain invaluable and irreplaceable historical information, they are first and foremost representations of the sacrifice U.S. service members have made for our country.