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A deep-sea training and engineering dive off the coast of San Diego provided an opportunity for never-before-seen imagery of the U.S. Navy submarine USS F-1, lost at sea in an accident on December 17, 1917, that resulted in the death of 19 crew members. The detailed, high-definition images of the final resting place of the WWI-era sub were made possible by a group of interagency teams, as well as advanced deep-sea imaging technology.

From February 24 to March 4, researchers from the Woods Hole Oceanographic Institution (WHOI) used the human-occupied vehicle (HOV) Alvin, and autonomous underwater vehicle (AUV) Sentry, both workhorses of the National Deep Submergence Facility (NDSF) underwater vehicle fleet, to capture up-close images of the more than 100 year-old wreck, located in approximately 400 meters (more than 1,300 feet) of water.

The U.S. National Science Foundation (NSF) supported the cruise to conduct Alvin and Sentry systems and engineering testing. During the cruise, the team completed meticulous surveys of the submarine using sonar systems on Sentry and the research vessel Atlantis, as well as video cameras on a tethered vehicle and still and video imaging systems on Alvin. The team also surveyed a Navy torpedo bomber training aircraft that crashed near the same location in 1950.

"Advanced ocean technology and simple teamwork played a big part in delivering these new images," said WHOI's Bruce Strickrott, manager of the Alvin Group at WHOI and the sub's senior pilot who helped lead the expedition.

"Once we identified the wreck and determined it was safe to dive, we were able to capture never-before-seen perspectives of the sub. As a U.S. Navy veteran, it was a profound honor to visit the wreck of the F-1 with our ONR and NHHC colleagues aboard Alvin."

The surveys and subsequent images of the wrecks were made possible by the expertise and support of partners from the Office of Naval Research (ONR), the University-National Oceanographic Laboratory System (UNOLS), NHHC, and WHOI. NSF funds the NDSF fleet with support from ONR and the National Oceanographic and Atmospheric Administration.

"The NDSF provides essential equipment for reaching the deep ocean," said Lisa Clough, the acting division director for the NSF Division of Ocean Sciences. "Although HOV Alvin and AUV Sentry are critical for revealing deep-sea geologic hazards and studying remote ecosystems, they also offer opportunities to train the next generation of scientists and uncover crucial moments from our nation's history."

The seven dives were part of a previously planned training and engineering mission conducted by the Alvin Team to give pilots-in-training time to hone their skills diving the submersible and to allow for the development of new technology and capabilities that serve the deep-sea research community.

The non-invasive, visual surveys of F-1 also took Naval History and Heritage Command (NHHC) Underwater Archaeologist Brad Krueger on his first Alvin dive, and first in-person dive on a historical wreck site. NHHC's mission is to preserve and present an accurate history of the U.S. Navy, which includes locating, interpreting, and protecting U.S. Navy ships and aircraft.

"It was an incredibly exciting and humbling experience to visit these historically significant wrecks and to honor the sacrifice of these brave American Sailors," said Krueger. "All of us at the NHHC are grateful for this collaboration, which also enabled us to document and assess the condition of the crafts."

"As a Navy veteran, making this dive—together with another Navy veteran and a Navy historian—was a solemn privilege," said ONR Program Officer Rob Sparrock, who was in the DSV Alvin as it surveyed and analyzed the sub. "Lasting nearly eight hours, there was time to contemplate the risks that all mariners, past and present, face. It also reminded me of the importance of these training dives, which leverage the knowledge from past dives, lessons learned and sound engineering."

A remembrance ceremony took place on board Atlantis above the location of the wreck after the dives. A bell rang out 19 times—one for each service member lost at sea. "History and archaeology are all about people and we felt it was important to read their names aloud," said Krueger. "The Navy has a solemn responsibility to ensure the legacies of its lost Sailors are remembered."

Rapidly improving imaging technology enhanced the team's ability to survey and document the F-1 wreck site. Multi-beam sonar systems on R/V Atlantis and AUV Sentry produced detailed, high-resolution maps of the wreck and surrounding seafloor.

Complementing this, high-resolution cameras on Alvin captured detailed video and still photos of the wreck that WHOI imaging specialists stitched into photogrammetric models capable of providing precise measurements of the sub and the animals that have colonized its wreckage over the years.

The use of new tools and techniques provided real-time training for use on future missions, including mapping strategies in complex seafloor topography.

This wealth of data and imagery allowed the ocean imaging team at WHOI to reconstruct the F-1 submarine using photogrammetry, resulting in stunning 3D models.

"While these depths were well within the dive capability for Alvin and Sentry, they were technical dives requiring specialized expertise and equipment," said Anna Michel, NDSF chief scientist and co-lead of the expedition. "We were careful and methodical in surveying these historical sites so that we could share these stunning images, while also maintaining the reverence these sites deserve."