Exploring Attu’s Underwater Battlefield and Offshore Environment

The expedition also focused on areas in and around the West Arm of Holtz Bay, located to the northeastern side of Attu. Despite multiple reports of sunken airplanes and watercraft, the SAS surveys revealed a mostly barren, sandy seafloor. In both Holtz and Massacre bays, the overall lack of identified wrecks corresponding to smaller vessels, such as aircraft, landing craft, and barges, came as a surprise, given the combination of Attu’s notorious ocean conditions during the war and the high-level of sonar resolution the project team was using in the present day. This suggests that these wrecks have been more adversely affected by decades of water movement, storm activity, and sediment burial, as compared to larger surface ships.

Further offshore, the research team explored deeper depths, mainly in search of Kotohira Maru, a 6,000-ton freighter carrying supplies from Japan that was bombed by an American weather plane on January 5, 1943. Prior to this project, there remained considerable debate as to how and exactly where this sinking took place, with many reputable secondary sources providing conflicting accounts. Despite war-era charts indicating its suspected location, the initial SAS surveys were unable to locate the doomed vessel. As such, the search area was increased, and after six hours of survey, the fairly-intact remains of Kotohira Maru were finally located in around 83 meters (275 feet) of water, over a kilometer from its last reported position. The high-resolution SAS imagery aligned perfectly with wartime records of this ship’s demise, demonstrating damage to the bow and starboard side. Structures such as the smokestack, masts, and counter stern were still upright in the water column, according to shadows seen in the sonar data. Once again, the ROV was deployed to make a visual confirmation of the wreck, which not only obtained photographic documentation of ship parts, but also revealed a rich benthic biota, largely dominated by anemones.

A second shipwreck of Japanese origins was located much closer to shore. Using the combination of an aerial drone and underwater ROV, the rusted remains of Cheribon Maru, a Japanese freighter sunk on Thanksgiving Day, 1942, by American aircraft, were observed. The ROV video revealed that the sunken shipwreck is host to a thriving community of kelp, making it difficult to identify individual vessel components. Unfortunately, the wreck site’s location in about 10 meters of water (33 feet) is beyond the minimal depth for sonar operations. The project’s success in locating the physical remains of both Kotohira Maru and Cheribon Maru is believed to mark a first in U.S. underwater archaeology. Unlike the Japanese shipwrecks at Kiska, which are clearly exposed above the sea surface, the Attu vessels are fully submerged, while their proximity to shore, as opposed to the aircraft carriers of Midway Island (Hawaii), means they are located within Alaska waters. This unique combination renders Kotohira Maru and Cheribon Maru the first Japanese World War II surface ships to be found completely under U.S. state waters. Both vessels are legally protected by the Sunken Military Craft Act (2004).