(Web Desk) - A World War I era U.S. Navy submarine now rests quietly more than 1,300 feet (396 meters) below the Pacific, west of San Diego.
The USS F-1 sank on 12/17/1917 after a collision during a training run, and 19 sailors died, according to Navy records.
A recent deep-ocean mission used modern tools to map the wreck in crisp detail, without disturbing it. The mission doubled as a training cruise for pilots and engineers who operate some of the most capable undersea vehicles in the world. Bruce Strickrott, from Woods Hole Oceanographic Institution (WHOI), helped lead piloting on the expedition.
He and partner teams documented the submarine’s hull and surrounding seafloor with high resolution video and photos.
The human-occupied vehicle Alvin can reach about 4 miles (6.5 kilometers) deep, which puts most of the seafloor within reach of its cameras.
That capacity made it possible to observe the site directly and plan safe, careful passes over sensitive features.
The first views showed that the submarine is still relatively intact, lying on one side of its hull, with key features still visible. Teams also noted seafloor life that has colonized the wreck over time.
The crew stitched thousands of overlapping images into precise 3D shapes using photogrammetry, a method that turns many pictures into accurate measurements. Those models help researchers estimate dimensions and track changes at the site over time.
An autonomous underwater vehicle called Sentry cruised low and steady to map the area with sonar before Alvin arrived.
Sentry is rated to operate down to about 19,685 feet (6 kilometers) and can run long, pre-planned survey lines with high stability. This is ideal for seafloor mapping and imaging.
After Sentry’s reconnaissance, the human-occupied vehicle (Alvin) flew slow, deliberate patterns over the wreck. Pilots balanced visibility, distance, and safety to avoid stirring sediment or contacting the hull.
A ship-mounted multibeam sonar built a wide-area map from the surface. That map guided Sentry’s lower altitude passes for finer detail, and helped the team plan Alvin’s flight lines.
Photogrammetric models capture the submarine’s dimensions within small margins of error when images overlap well and light is even. Those constraints pushed the team to use steady speeds, stable altitudes, and consistent camera settings during each run.