After a week of sifting through the wreckage, investigators may be close to helping to fulfil the US military's promise to recover all prisoners of war and combat casualties, no matter how long it takes.

"It's a question of honour for the American armed forces: you never leave someone on the battlefield. It's a promise we keep, even today, 75 years later," said Simon Hankinson, the US consul general in Marseille.

He was aboard the French Navy's Pluton anti-mine and diving ship on Monday as the team wrapped up its mission to identify the pilot.

Ten French divers have been assisting the American team since June 25, bringing up pieces of wreckage and vacuuming up sediment some 18 metres (60 feet) below the surface on Corsica's eastern coast, about 40 kilometres (25 miles) south of the capital Bastia.

Discovered in the 1980s, the plane's wreckage and number were photographed by a diver in 2012, eventually coming to the attention of the US agency in charge of seeking out prisoners of war and soldiers missing in action.

"Recovery projects take many years to develop," said Lieutenant Dan Friedman, who led the project for the US Defense POW/MIA Accounting Agency (DPAA). He said archaeologists first searched the site in 2014.

Another P-47 lies about 30 metres away, but its pilot was able to eject in time.

- 'We found a lot' -

The recovery agency estimates 83,000 prisoners or missing have not been found since World War II, of whom 27,500 are thought to be in Mediterranean waters.

Of those, about 8,000 bodies are thought to be recoverable, and the agency has an annual budget of roughly $150 million (130 million euros) to pursue those cases.

On the seabed off Corsica, a metal grid has been installed to mark off research zones, with divers using enormous tubes to suck up the seafloor and deposit their findings in a huge metal recipient floating on the surface.

Researchers then use dozens of black buckets to spread the sediment across a sieve, their hands picking through tiny piles of metal with the focus of miners searching for gold.

"After we screen all the sediment that comes from the bottom, we separate the potential evidence and then we do a more thorough deep cleaning, to see if there might be a serial number," said Ezra Swanson, a 30-year-old US Army engineer.

The findings, including bones, a watch and part of the pilot's identifying "dog tags", will later be sent to a DPAA lab in Hawaii or Nebraska for potential DNA analysis.

"It's like a police investigation, it's evidence, so we have to keep it until we solve the case," said Peter Bojakowski, a marine archaeologist with the agency.

"We found a lot, enough evidence to most likely identify the pilot, but everything has to go to the lab for DNA tests," he said.

If the results are conclusive, the pilot's remains will be buried according to the family's wishes, either at the Arlington National Cemetery near Washington or at one of the several American military cemeteries in France.

"When we discover the body of someone who's been dead for 75 years, it's upsetting for the family... but it allows them to find closure to the story," Hankinson said.