The graves of 30 World War II Marines and sailors killed during the 1943 assault on the island of Betio, part of the Pacific atoll of Tarawa, have been located.

Audrey McAvoy at the Associated Press reports that the remains were discovered in March by searchers from the non-profit organization History Flight, a group dedicated to recovering the remains of missing American service members.

It’s believed most of the remains belonged to members of the 6th Marine Regiment. The Defense POW/MIA Accounting Agency announced it will recover the bodies in July and bring them to its lab in Hawaii. There, forensic anthropologists will use DNA, dental records and other evidence to try and identify the remains.

History Flight was given permission to demolish an abandoned building during its search, and most of the remains were found underneath that structure. Many of the remains were found under the water table, meaning the team had to continuously pump water out of the excavation site during the dig.

These weren’t the first remains found on Betio. Ryan Prior at CNN reports that History Flight has been working in Tarawa, now a part of the nation of Kiribati, since 2007. In 2015, the group uncovered the bodies of 35 U.S. military personnel, including Medal of Honor winner 1st Lt. Alexander Bonnyman Jr., who led a hopeless assault on a Japanese bunker during the invasion, losing his life in the process. In 2017, the group found another 24 sets of remains. In total, the organization has found and exhumed the remains of 272 Marines and sailors from the island over the last decade. They believe there are about 270 remains still to be found on the island.

In total, more than 990 Marines and 30 sailors were killed during the three-day amphibious assault on the island. Most were buried in makeshift graveyards on the island, which originally included identifying markers. But Navy construction battalion sailors removed the markers when they hastily built airfields and other infrastructure on the island to aid in the war effort. McAvoy reports that in the late 1940s, the Army Graves Registration Service exhumed some of the bodies buried on Tarawa and moved them to a National Cemetery in Hawaii, placing many bodies in graves marked as unknown. In 1949, the military informed 500 families that the bodies of their loved ones still on Betio were unrecoverable.

Mark Noah, the president of History Flight, tells Prior that his organization doesn’t accept that answer. Since 2003, History Flight has used military documents, eyewitness accounts, cadaver dogs and ground penetrating radar to find the remains of some of the 78,000 service members listed as missing since World War II, though most of their focus has been on Tarawa, where they’ve excavated at least 11 sites containing remains over the past decade.

“The investment of 10 years of work and $6.5 million has resulted in the recovery of extremely significant, but not yet to be disclosed, number of missing American service personnel,” Noah said in a press release after the 2017 recovery. “Our trans-disciplinary team — including many volunteers — of forensic anthropologists, geophysicists, historians, surveyors, anthropologists, forensic odontologists, unexploded ordnance specialists, medics and even a cadaver-dog handler have excelled in difficult conditions to produce spectacular results.”

Tarawa, part of the Gilbert Islands, was one of the first stops on the United States’ Central Pacific Campaign. The idea was to secure the Gilberts as a stepping stone and base of operations to invade the Marshall Islands, then the Marianas, then the Japanese homeland itself. The key to the Gilberts was little Betio Island, where 4,500 Japanese troops were dug in.

The U.S. military believed taking the atoll would be a relatively simple operation. It wasn’t. Marine landing craft got stuck on coral reefs during low tide, and the men had to slog their way to the beach under heavy gunfire. Disabled amphibious vehicles blocked the invasion route, slowing things down even further. As the tide rose and the Marines finally began to push in, the remaining Japanese troops launched an all-out banzai attack.

In total, 1,000 Americans lost their lives in the invasion, and 2,000 were wounded over the course of three-day attack. The heavy casualties inflicted from taking a tiny island illustrated the brutality of the island-hopping campaign. It also taught military commanders lessons about “Atoll War” that they would apply to the many similar assaults still to come.