On a foggy December morning in 1917, three U.S. Navy submarines crept through the waters off the coast of San Diego. They were testing their limits—running performance trials in the shadow of World War I. Then came a collision. In less than ten seconds, the USS F-1 vanished beneath the waves.

Now, more than a century later, the lost submarine has resurfaced—virtually.

In a deep-sea mission carried out earlier this year, researchers from the Woods Hole Oceanographic Institution (WHOI), in collaboration with the U.S. Navy, returned to the wreck site. Using state-of-the-art imaging tools aboard two submersibles, they captured the most detailed views ever recorded of the F-1’s final resting place.

“It was a profound honor to visit the wreck of the F-1,” said Bruce Strickrott, senior pilot of Alvin, WHOI’s human-occupied submersible. “Advanced ocean technology and simple teamwork played a big part in delivering these new images.”

A WWI Submarine’s Sudden End

The USS F-1 was barely six years old when it sank. Built in 1909 and launched in 1911, the 43-meter (142-foot) submarine was part of America’s early undersea fleet—a war machine still in its infancy when the United States joined World War I in 1917.

On December 17 of that year, the F-1 was conducting a 48-hour “engineering run and performance test” off the coast of La Jolla, California. Two other submarines—USS F-2 and USS F-3—were running similar exercises nearby.

Then, as Bradley Krueger, a senior archaeologist with the Naval History and Heritage Command, explained to Live Science, “All three vessels entered a fog bank. USS F-3 collided with USS F-1, and following the collision USS F-3 remained on scene to help rescue survivors from the water.”

It was too late. The F-1 went down instantly. Only five men survived.

For decades, the wreck remained hidden. It was accidentally rediscovered in 1972, when a Navy underwater vehicle searching for a crashed jet stumbled across the sub’s remains. “It looked like a big ax had hit her,” the pilot said at the time.

Into the Deep

Earlier this year, from February 24 to March 4, a team of scientists and engineers finally returned for a closer look. Launched from the research vessel Atlantis, they sent down Alvin and an autonomous vehicle named Sentry to a depth of close to 400 meters (1,300 feet)—too deep for traditional scuba divers.

The mission was part of a scheduled training expedition funded by the National Science Foundation, the Office of Naval Research, and the University-National Oceanographic Laboratory System. But it offered far more than training.

Using sonar, still photography, and video, the team surveyed the wreck of the F-1, which still lies on its right side, bow pointed northwest. Despite spending 107 years underwater, it is “remarkably intact,” Strickrott said.

The WHOI imaging team used thousands of 2D images to create a 3D photogrammetric model—a digital reconstruction that offers a ghostly, yet precise, view of the hull, conning tower, and the jagged wound that sunk the vessel.

“It was an incredibly exciting and humbling experience to visit these historically significant wrecks and to honor the sacrifice of these brave American Sailors,” Krueger said.

A Second Wreck

The team found more than just the F-1.

A few miles from the sub, Alvin’s cameras also captured the remains of a Grumman TBF Avenger—a World War II-era torpedo bomber that vanished during a training flight in 1950. The crash had been known to WHOI for years, but the U.S. Navy hadn’t formally recorded its location.

With the new images, the Navy confirmed the plane’s identity and confirmed that no lives were lost in that incident. Strickrott noted a curious detail: the number “13” was stenciled on the aircraft’s engine nacelle. “An obvious superstitious element,” he said, before revealing the truth: it referred to the training squadron.

History, Science, and Legacy

Though the mission began as a technical test, it quickly became a showcase of modern deep-sea imaging.

Using sonar, stills, and video from Alvin and Sentry, researchers created detailed 3D models of the F-1 and nearby Avenger bomber. These digital reconstructions allow scientists to measure and monitor wreck sites with precision.

“These were technical dives requiring specialized expertise and equipment,” said Anna Michel, chief scientist of the expedition. The tools and data will now inform future missions, from seafloor mapping to deep-ocean archaeology.

The technology also helped confirm the exact identity and location of the Avenger, which had remained uncertain for decades. What once existed only in aging records now lives as a fully mapped site—accurate to the centimeter.