108-year-old sunken submarine was finally found, but the footage reveals something shocking

When the Woods Hole Oceanographic Institution's humanoccupied vehicle Alvin and its companion autonomous underwater vehicle Sentry descended to the sandy bottom west of San Diego in early spring of 2025, no one on the deck of the research vessel Atlantis quite knew what to expect. The deep sea training mission would soon yield highdefinition images of one of the most poignant wrecks in United States naval history. The century old submarine USS F1, also known by her hole number SS20. Stricken in 1917 after colliding with her sister boat, the F3, the F1 lay forgotten nearly 300 fathoms deep, her rusty silhouette claimed by marine life and sediment. The mission's success capturing never-before-seen footage and constructing a photogometric three-dimensional model of the submarine would not only advance submersible technology and pilot training, but also give voice once more to the 19 sailors who perished when America's first wartime submarine was lost. A wartime tragedy rediscovered in the spring of 1917. The young US Navy submarine force was expanding rapidly in response to America's entry into the Great War. The F-class submarines F1 through F4 represented the service's first foray into larger oceangoing attack boats. The F1, commissioned in 1915, measured just over 100 ft long, displaced 200 tons on the surface, and could dive to depths of 200 f feet. In late March 1917, F1 and her sister F3 were conducting a routine training exercise off Point Loma, California, practicing submerged approaches and navigational drills in the cool Pacific water when disaster struck. The two boats collided. In the confusion of heavy swell and limited communication, the F3 rammed the F1, crushing her bow and causing catastrophic flooding. Despite valiant efforts by her crew, the F1 slipped beneath the waves, settling upright in approximately 1,300 ft of water, 19 sailors trapped within her forward compartments were unable to escape. The tragedy marked the Navy's first wartime submarine laws, a somber milestone in undersea warfare. Official inquiries and safety reforms followed, but the wreck itself remained inaccessible until its rediscovery by the National Oceanic and Atmospheric Administration in 1975, which mapped its approximate location by Sidcan sonar. For decades thereafter, the wreck lay undisturbed, an underwater memorial slowly being reclaimed by barnacles, corals, and sea an enemies advancing deep sea exploration. Nearly 50 years after that initial discovery, technological advances made it possible to revisit the F1 with eyes and instruments capable of revealing her condition in unprecedented detail. The Atlantis expedition of February and March 2025 had two primary goals. to train the next generation of Alvin pilots and engineers in operating at extreme depths and to test Sentry, an autonomous glider equipped with highresolution cameras and sonar. Amidst these training objectives, principal scientist Anna Michelle and her colleagues at the National Deep Submergence Facility saw an opportunity. Document the F1 wreck photogometrically. Photoggramometry. The art of creating precise three-dimensional models from overlapping two-dimensional images has revolutionized maritime archaeology. By taking hundreds of highresolution stills at known positions, imaging specialists can reconstruct a wreck's entire structure with centimeter accuracy. This technique had already proven successful on wooden wrecks in European waters and on deep ocean features. Applying it to the F1 promised not only a detailed record of the submarine's current state, but also quantitative data on deterioration rates, marine growth patterns, and structural integrity information vital to preserving other deep sea heritage sites. Descending into history, on a clear winter morning, Alvin's crew prepared the submersible for its dive. Alvin, with its familiar orange and black hull and threeperson capacity, has been in service since 1964, earning a reputation for reliability. Alongside it, Centria, roughly meterlong torpedo-shaped robot, would follow the Rex outline, mapping with a forward-looking multi-beam sonar that sent out fan-shaped pulses and recorded the echoes. The day's dive team included Michelle Rob Sparro, a program officer with the Office of Naval Research and a former submariner, and Brad Krueger, an underwater archaeologist from the Naval History and Heritage Command. For Krueger and Sparro, visiting F1 was deeply personal a chance to pay respects to lost comrades and to confront the everpresent risks beneath the waves. After a three and a half hour descent in Alvin, the wreck emerged from darkness like a steel phantom. Resting upright on the sandy flat, the submarine's bow had collapsed inward, its conning tower partially caved, and the stern sections twin propellers still attached but bent outward. Thin striations of corrosion etched the hall, while ropelike clusters of hydroids and bright anemmones clung to every available surface. Schools of small fish darted through the broken hatches, and larger predators, rockf fish, and California sheep head patrolled the nearby water column. The dive team spent some time simply absorbing the site. "There is a reverence you feel when you hover overhead," Krueger later recalled. "This was the last resting place of sailors who never overhead. Got to see home again." In the cramped Alvin cabin, the scientists took turns capturing highresolution video and still photos from multiple angles, illuminating details as small as the stamped hall number 20F near the torpedo tubes. From images to immersive models back aboard Atlantis, the photoggramometry team set to work. Over the next several weeks, they processed more than a thousand images, feeding them into specialized software that matched overlapping features and calculated the precise position of each pixel in three-dimensional space. The resulting model allowed researchers to measure the thickness of hull plating, map the growth of marine organisms, and even gauge the extent of sediment accumulation around the keel. With millimeter scale accuracy, they could record the angle of the submarine's tilt just a few degrees off vertical and note how deep sand had drifted into the forward compartments. Sentry sonar runs added another layer of data by emitting sound pulses and recording return time. Sentry generated a continuous bathometric map of the surrounding seafloor. Combined with Alvin's optical images, the team built a comprehensive site plan showing F1 in context. the gently sloping benthic plane, nearby rock outcrops favored by corals, and faint tracks in the sediment left by bottom dwelling rays, honoring lost sailors. But these scientific achievements were only part of the story. On the final day of the cruise, the crew held a remembrance ceremony aboard Atlantis. As the research vessel drifted over F1's location, a brass ship's bell was gently rung 19 times once for each sailor lost in the collision. Anna Michelle read their names drawn from Navy muster rolls. Her voice carried by the wind into the Pacific expand. Rob Sparro sitting beside her reflected on the evolution of submarine safety protocols over the past century and how each memorial dive underscores the human cost of progress. For me, Sparox said later, it was a solemn privilege. The risks these submariners took working in the early days of undersea warfare, the foundation of modern submersible exploration. Their service made Alvin possible. Krueger nodded in agreement. Archaeology and history are about people. This site isn't just metal on sand. It's a testament to lives interrupted, families left waiting. We owe them our vigilance. A legacy of exploration and remembrance. The newly acquired footage and photoggramometric models of F1 will now inform multiple fields. Naval engineers studying hull corrosion can compare on-site measurements with lab age steel samples. Marine biologists will analyze a species colonizing the wreck, offering insights into deep sea ecosystem dynamics. Historians and educators can use the digital reconstructions to create virtual reality experiences, allowing students and museum visitors to dive on F1 from anywhere in the world. Moreover, the mission success paves the way for future archaeological investigations of other deep sea wrecks, both military and civilian. From 20th century freighters to ancient trading vessels, the combination of Alvin's human perspective and centuries autonomous mapping offers a powerful toolkit for exploring and protecting her submerged heritage. As Atlanta's steamed home to Woods Hole, the deep sea team reflected on the broader significance of their work. The press releases would highlight highdefinition imagery and cutting edge photoggramometry. Technical papers would detail sonar methodologies and whole fatigue analyses. But above all, the researchers understood that every dive on F1 is a reminder. Beneath the waves lie chronicles of bravery and tragedy, waiting for careful eyes and respectful hands to bring them to light. 19 souls rest eternally in the submarine steel womb. Through modern technology and unwavering dedication, their story emerges again etched in rust and marine growth and now preserved in digital pixels for generations to How?