WASHINGTON, D.C. –
The Navy announced its findings into what sank the World War I cruiser USS San Diego (ACR 6) after a two-year study at the American Geophysical Union’s fall meeting on Dec. 11.
Dr. Alexis Catsambis, an underwater archeologist at the Naval History and Heritage Command, based at the Washington Navy Yard, led the project and chaired a panel discussion about the findings at the event. Although the original court of inquiry believed the explosion that sank the 500-foot armored cruiser was caused by a mine, later speculation raised the theory that it might have been a torpedo.
Dr. Ken Nahshon, an engineer in Carderock’s Hull Response and Protection Branch, and Dr. Arthur Trembanis, an associate professor at the University of Delaware’s College of Earth, Ocean and Environment in Newark, sat on the panel discussion to answer questions about the research.
After examining new survey data, additional archival research, computer impact and flooding models, the area of the ocean floor in which the wreck rests, and other elements related to the ship’s loss, Catsambis announced that the research team believed the explosion’s cause was a mine.
“The legacy of the incident is that six men lost their lives on July 18, 1918,” Catsambis said. “With this project we had an opportunity to set the story straight and by doing so, honor their memory and also validate the fact that the men onboard did everything right in the lead up to the attack, as well as in the response. The fact that we lost six men out of upwards of 1,100 is a testament to how well they responded to the attack.”
Researchers from Naval Surface Warfare Center, Carderock Division (NSWC Carderock) in West Bethesda, Maryland, using Naval Innovative Science and Engineering (NISE)/Section 219 funds, provided engineering support to the Navy History and Heritage Command to help determine the cause of San Diego’s sinking.
Using historical analysis, archaeological research, site investigation and Carderock-developed impact and flood modeling tools, the research teams were able to eliminate other possibilities that might have caused San Diego’s sinking such as sabotage, accident or enemy torpedo.
Trembanis explained how the use of underwater robotics and remotely deployed instruments, including an autonomous underwater vehicle, allowed researchers to collect high-resolution 3D images of the site to support their conclusion. Nahshon worked with Michael Kipp, an engineer from Carderock’s Weights, Stability and Reliability Branch, as principal investigators in analyzing field survey results and weapons attack and flooding sequences relating to San Diego. Together with Jeevan Nalli and Benjamin Ridenour of Carderock’s Vulnerability Assessment Branch, they were able to integrate software tools for performing whole-ship dynamic flooding (FLMASA-Flooding Model Advanced Stability Algorithm) and vulnerability analysis (ASAP—Advanced Survivability Assessment Program), for the development of a common vulnerability and flooding model, ultimately creating a digital twin of a damaged ship.
Nahshon said they were able to compare the 3D modeling data to the initial undamaged state of San Diego, and using the dynamic flooding software along with weapons effects assessment, they could calculate flooding patterns and quantify the loss of stability resulting in capsizing and sinking of the ship.
“The format of the 3D modeling data makes analysis readily comparable, but below-water collecting of 3D data at the sea floor is very challenging and requires immense expertise to interpret. Through this NISE project, we have gained valuable experience in both understanding how this data is collected and processing the results to inform damaged ship assessments,” Nahshon said.
Before taking questions, Catsambis shared why this research is important for the U.S. Navy and how learning from the past will help to prepare for the future.
“The collection of archeological and hydrographic data establishes a baseline, informing site formation processes and management of USS San Diego,” Catsambis said. “Lessons learned here are applicable to other U.S. Navy sunken military craft. This endeavor also provided real-world training opportunities for U.S. Navy divers, archaeologists, historians, modelers, naval engineers and graduate students.”
In July 1918, the 15,000-ton armored cruiser San Diego sank off Long Island, New York, losing six sailors from a crew of 1,100. German submarines had mined the coast, implicating a mine. But the ship’s captain was perplexed that the explosion occurred aft of the ship’s widest point, which gave rise to the notion the explosion might have been caused by a torpedo even though no submarine or torpedo trail had been spotted.
Later theories suggested a coal bunker explosion or sabotage, but the source of the explosion remained a mystery.
To commemorate the 100th anniversary of the loss of San Diego, the only major U.S. warship sunk in World War I, a multi-partner investigative campaign dubbed the USS San Diego Project was launched in 2017—mapping the wreck, assessing the wreck’s state of preservation, modeling its sinking and uncovering the weapon that likely sank it.
Kelley Stirling from NSWC Carderock Division contributed to this article.