Underwater robots are helping researchers and volunteers discover the watery resting places of soldiers who have been missing since World War II.
The initiative, called "Project Recover," uses autonomous robots equipped with sonar and cameras to scour the ocean floor. In March, the team found two World War II planes that had crashed over the Pacific.
"It was certainly a humbling experience, just knowing you're the first person to reach this wreck in 70 years," Eric Terrill, a researcher at the Scripps Institution of Oceanography who works with Project Recover, told Live Science. [ See photos of the World War II plane wrecks ]
The project concentrates its efforts around the Republic of Palau, a chain of islands in the Western Pacific, where some of the most intense fighting during the Pacific campaign of World War II happened.
In one month alone, there were more than 5,000 casualties during the fight for the island of Peleliu, which makes up part of the Palau chain. Historians estimate that more than 30 U.S. carriers, aircraft and sunken landing craft remain missing somewhere in the waters off Palau. The Project Recover team thinks there are 70 to 80 soldiers who potentially could be recovered from within those vessels.
"The only thing worse than going off to participate in a war is, going off to participate in a war and never getting to come home," Casey Doyle, a volunteer who works with the project, said in a video produced by camera maker GoPro, one of the project's sponsors.
But how does anyone track down a plane that crashed in the open ocean more than 70 years ago?
The hunt begins
Back in 2010, Terrill and Mark Moline, director of the School of Marine Science and Policy at the University of Delaware, started taking annual treks to the Palau island chain to study currents and map the flow of water around the islands. The researchers were using sophisticated technology to research the influence of super typhoons on coral reefs and to study how climate change impacts islands.
On one of these treks, they encountered Patrick Scannon, the founder of the nonprofit group BentProp. BentProp's mission is "to repatriate every American service member who has not come home."
The organization relies on historical data and firsthand accounts for its recovery work. Since the early 1990s, Scannon and a group of volunteers have been slowly filling in ocean floor maps based on data they collect from dives.
It was clear that it was tedious work, Moline said, and that's when he and Terrill realized they could help. Combining BentProp's historical data with Moline and Terrill's more sophisticated technology and detailed maps made it much easier to track where currents may have laid to rest long-lost World War II vessels. The two groups joined forces in 2012 and created Project Recover.
Searching for veterans
Project Recover uses a fleet of autonomous underwater vehicles (AUVs) to sweep the ocean floor around Palau. Each underwater robot is equipped with sonar readers and cameras that capture images of things like coral reefs, marine life and possibly missing World War II vessels and aircraft.
The torpedo-shaped robots allow the group to create detailed maps of the seafloor. Each underwater drone shoots out sound waves that reach 150 feet (46 meters) on either side. The sound waves bounce back at different strengths and frequencies, depending on what kind of material they collide with, Moline said.
"Some of these aircraft hit the water [at] around 150 mph [240 km/h], so some of them don't look like airplanes anymore," Moline told Live Science. "They look very similar to coral reefs."
But when the sonar hits metal instead of sediment or reef, it bounces back with a very different intensity, Moline said. The autonomous robots can skim along the bottom and produce higher-resolution images than if they were being towed through the open water, behind a boat.
Once the robots map out a promising location, the team sends in divers with handheld sonar devices to conduct a more thorough search of the area.
In March, after poring over national archives data, interviews with veterans and ocean current and plane trajectory analyses, the team found a World War II Avenger bomber that had been missing for 70 years. A Palau elder remembered seeing the plane go down. One of the soldiers made it out, but the aircraft went down with two men still inside, the researchers said.
"We were approaching what is hallowed ground," Terrill said while recounting the experience in the GoPro video. "Two of our guys are still on board that aircraft."
Sonar images revealed another sunken aircraft — a so-called F6F Hellcat — nearby.
Project Recover doesn't actually touch the wrecks, Moline said. Following the discovery, the researchers submitted reports for both recovered vessels to the U.S. Navy. In total, there are approximately 78,000 missing servicemen from World War II, with potential recovery sites all around the globe. Navy personnel review these reports, decide which ones are retrievable and then notify families if they are able to identify the veterans.
Moline said there seems to be a lot of interest in the two sites discovered by Project Recover, since the researchers were able to submit such detailed reports.
Terrill said that, with so many soldiers missing in action, there's clearly a need to develop this kind of search-and-recovery method, and the project is acting as a test bed for search technologies. The next Project Recover mission will launch in March 2015, and the group has four or five promising search sites to target.
"You spend so much time and effort putting together a forensic case file that when you finally find something, it's really rewarding," Moline said. "But there's a pause, because you know you've just found some people that have sacrificed their lives — so there's mixed emotions when do you find it."
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