Photogrammetric reconstruction of the submarine USS F-1 on the seafloor west of San Diego, California. CREDIT: Image by Zoe Daheron, ©Woods Hole Oceanographic Institution. Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday. In 1917, two US submarines collided off the coast of San Diego and submarine USS F-1 sank to the bottom of the Pacific Ocean, along with 19 crew members aboard. The horrible accident, whose wreckage was discovered in 1975, represents the US Naval Submarine Force’s first wartime submarine loss. Now, researchers from Woods Hole Oceanographic Institution have captured new footage of the 1,300 feet-deep underwater archaeological site. “They were technical dives requiring specialized expertise and equipment,” Anna Michel, a co-lead of the expedition and chief scientist at the National Deep Submergence Facility, said in a statement. “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.” The high-definition imagining and mapping of the USS F-1 took place during a deep-sea training and engineering mission in February and March. The missions aimed to train future submersible pilots and test the human-occupied vehicle Alvin and autonomous underwater vehicle Sentry.  The team captured never-seen-before images and videos and conducted a sonar survey, which essentially consists of mapping a region by shooting sound waves at it and registering the echo. Imaging specialists combined the 2D images into a 3D model of the wreck—a technique called photogrammetry. Using photogrammetry reveals measurements not just of the submarine but of the marine life that over the past century has claimed the vessel as its own.  Photogrammetric reconstruction of the submarine USS F-1 showing the sub’s stern and propeller. CREDIT: Image by Zoe Daheron, ©Woods Hole Oceanographic Institution. “As a Navy veteran, making this dive—together with another Navy veteran and a Navy historian—was a solemn privilege,” said Office of Naval Research Program Officer Rob Sparrock, who was in Alvin when it went down to the wreck. “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.” The researchers also investigated a Navy torpedo bomber training aircraft that went down in the region in 1950. After the dives, they held a remembrance ceremony aboard the research vessel Atlantis during which a bell rang once for each of the crew members lost in 1917.  “History and archaeology are all about people and we felt it was important to read their names aloud,” said Naval History and Heritage Command Underwater Archaeologist Brad Krueger, who also dove in Alvin. “The Navy has a solemn responsibility to ensure the legacies of its lost Sailors are remembered.” #108yearold #submarine #wreck #seen #stunning