The remains of 36 U.S. Marine heroes of a bloody World War II battle were found on an isolated island in the Pacific more than 70 years after they died, various news outlets report.

Mark Noah, director of Florida-based non-profit History Flight Inc., reportedly told Radio New Zealand that a four-month excavation on Betio Island in Kiribati resulted in the discovery of the warriors’ bodies.

The U.S. Marines were killed during the fierce Battle of Tarawa in November 1943, said Noah, whose organization worked in coordination with the U.S. Defense Department on the recovery efforts.

“(They) had an expectation that if they were to die in the line of duty defending their country they would be brought home… that was a promise made 70 years ago that we felt should be kept,” Noah reportedly said on Tuesday.

He added that the remains, although they nave not been officially identified, almost indubitably include those of 1st Lt. Alexander Bonnyman, who was posthumously awarded the Medal of Honor, America’s highest military accolade, for conspicuous gallantry.

“Bonnyman’s citation says he led a series of assaults when Marines stormed the island, finally falling when he attacked a bombproof installation that was hampering the advance,” notes Agence France-Presse (AFP).

“Overall, more than 1,000 Americans died at Tarawa, while the entire Japanese garrison of 4,800 was wiped out,” it adds.

Bonnyman was presumed buried at sea.

“The archaeological team found the mass grave using magnatomatry, radar scans, cadaver dogs, and interviews with surviving veterans of the battle,” notes The Associated Press (AP).

Several hundred U.S. troops were buried in make-shift, unrecorded graves after the Tarawa battle where they still lay, according to Noah.

The late Lt. Bonnyman’s “tale begins on Dec. 7, 1941, when the Japanese bombed Pearl Harbor. Sandy Bonnyman was a miner near Santa Fe, N.M. He had already served a stint in the Army and was now 31 years old. But when he heard the news, he reenlisted, this time in the Marines,” reports The Washington Post.

“By the time he landed on Tarawa Atoll, a string of strategically important islands in the middle of the Pacific, Bonnyman was the executive officer of the 2nd Battalion, 8th Marines’ Shore Party,” it adds. “For three days in late November 1943, the Marines tried to take Betio from the Japanese. Bonnyman led his party across the island, destroying enemy outposts as he went.”

Clay Bonnyman Evans was present when the lieutenant’s body was uncovered, according to The Post. Evans, a former Daily Camera reporter and editor, is the war hero’s grandson.

“Bonnyman’s remains will be flown to a military lab in Hawaii in July, and returned to the family by the end of August,” reports Daily Camera. “He will then be buried at the family plot in Knoxville in late September, in one of the empty plots underneath that large marble monument bearing those false words about his final resting place.”