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ThayerMahan technology enables Aleutian Islands discovery of Japanese vessels sunk in only WW II battle fought on U.S. territory

Images of the Japanese vessel Kotohira-Maru provided by ThayerMahan's exceedingly high-resolution sonar. The technology enabled the identification of many smaller targets, most of which would be impossible to see using more traditional forms of remote sensing

GROTON, Conn., Oct. 30, 2024 /PRNewswire/ -- ThayerMahan, a world leader in providing autonomous maritime surveillance solutions for the defense and offshore wind energy sectors, provided its advanced synthetic aperture sonar to a research team that discovered World War II Japanese and U.S. vessels off the Aleutian Island of Attu involved in the only battle to take place on U.S. territory.

The foreign vessels are the only Japanese military ships believed to be situated within U.S. state waters. The research marked the first underwater archaeological survey around Attu and marks the beginning of what is sure to be an increased focus on the oft-forgotten Aleutian Island campaign and by extension Alaska's World War II history.

The Battle of Attu is also known as the "Forgotten Battle" because it was eclipsed by larger campaigns in the Pacific Theatre.

The project, entitled "Exploring Attu's Underwater Battlefield and Offshore Environment," was led by Dr. Dominic Bush, Research Associate with Ships of Discovery, Inc., Dr. Jason Raupp, Assistant Professor of Maritime Studies in East Carolina University's Department of History, and Dr. Caroline Funk, Assistant Research Professor at University of Buffalo in July.

Using ThayerMahan's cutting-edge survey technology, the team of archaeologists, hydrographers, and robotic engineers located three World War II-era shipwrecks. ThayerMahan's exceedingly high-resolution sonar also enabled the identification of many smaller targets, most of which would be impossible to see using more traditional forms of remote sensing.

The seafloor around Attu is littered with vestiges of World War II, including dozens of anchors, chain, mooring blocks, and sunken buoys, as well as examples of materials used in base construction, such as timbers, piping, and cable. Perhaps most interesting was the numerous sections of anti-submarine netting that could be clearly discerned. With the centimeter resolution offered by synthetic aperture sonar, the interconnected metal rings of these nets, reminiscent of chainmail armor, were documented in stunning detail. The ThayerMahan technology was used in tandem with a newly developed camera system for remotely operated vehicles provided by World Scan Project.

Though fighting on the Aleutian Island was limited to three weeks in May 1943, Attu had been the site of significant military activity ever since its invasion by the Japanese military on June 7, 1942. That offensive marked the first time a foreign power occupied U.S. territory in North America since the War of 1812 – a feat that has not since been repeated. Following the liberation of the remote island by American forces, it was transformed into a military outpost that operated throughout the war's duration.

The first vessel located was the Kotohira Maru, a 5,000-ton freighter that carried provisions, housing materials, and fuel for Japanese troops stationed on Attu. It was sunk by a U.S. Navy weather plane on January 5, 1943, with only two of its crew rescued. Despite war-era charts indicating its suspected location, the survey team located the fairly intact remains of Kotohira Maru over a kilometer from its last reported position, in nearly 300 feet (80 meters) of water.

Closer to shore, Yasumasa Ichikawa, Chief Technical Officer of World Scan Project, utilized a combination of aerial and underwater drones to inspect the purported location of the second Japanese shipwreck, Cheribon Maru. Draped in kelp and other marine growth, the remains of the 3,000-ton freighter, sunk on Thanksgiving Day 1942 by American bombers, were observed in less than 30 feet (9 meters) of water. At least 15 crew members perished during the sinking, with some estimates as high as 55.

The lone American ship located was the U.S. Army cable layer SS Dellwood, whose discovery came 81 years to the day of its sinking. The nearly 3,500-ton ship had struck a submerged pinnacle on July 19, 1943, and sank while being towed to a nearby dock. Both sonar and ROV imagery revealed the severely disarticulated state of the former cable ship, likely the result of post-wrecking bombing as it had become a navigational hazard. Now resting over 100 feet (30 meters) below the sea surface, SS Dellwood provides a unique glimpse into U.S. military operations in the Aleutians after the battle.

The project was funded through complementary grants from NOAA Ocean Exploration and the U.S. National Park Service American Battlefield Protections Program.

Research contacts:

Dr. Jason T. Raupp, Assistant Professor, Program in Maritime Studies, East Carolina University rauppj14@ecu.edu
Dr. Dominic Bush, Research Associate, Ship of Discovery, Inc. Dbush@alumni.nd.edu
Dr. Caroline Funk, Assistant Research Professor, University of Buffalo cfunk@buffalo.edu