Retired Marine Col. Gene Castagnetti fought side by side with South Vietnamese soldiers when he was an adviser during the Vietnam War in 1965-66.

On Saturday the Honolulu resident will honor that long-ago brotherhood in Westminster, Calif., when the remains of 81 unidentified soldiers from a South Vietnamese airborne battalion killed in action in late 1965 will be memorialized and buried with full military honors.

Giving the casualties a final resting place on America soil follows a decades-long journey from Vietnam to Thailand to Hawaii to Westminster — part of Orange County’s “Little Saigon” where more than 190,000 Vietnamese live.

Former Army of the Republic of Vietnam, or ARVN, soldiers will escort the remains at Sid Goldstein Freedom Park, which honors American and South Vietnamese war veterans. The ceremony will include a rifle salute and taps. Following that, the remains will be laid to rest under a commemorative marker at nearby Westminster Memorial Park cemetery.

Navy Secretary Richard Spencer is expected to be one of the speakers.

“This final resting place will mark a complicated 54-year journey that began on a long-forgotten battlefield during a vicious war that tore apart our country and resulted in the deaths of 58,000 Americans and millions of Vietnamese,” former Navy secretary, U.S. senator and Vietnam veteran Jim Webb said in a recent USA Today opinion piece.

For decades the ARVN remains — mostly small bone fragments — had been kept at the Defense POW/MIA Accounting Agency’s lab at Joint Base Pearl Harbor-Hickam, according to Webb.

Twice, the Socialist Republic of Vietnam rejected their return, Castagnetti said.

The government was asked, “Would you like the ARVN remains to be returned for burial in Vietnam?” said Castagnetti, former director of the Veteran Affairs cemetery on Oahu known as Punchbowl. “The answer was basically, ‘No, they are puppets of the American government.’”

Castagnetti, who received a Silver Star for bravery on a second tour to Vietnam in 1969-70, worked with Webb on the burial effort and assisted with the Sept. 13 offload of the remains from an Air Force C-17 cargo aircraft that flew from Hawaii to March Air Reserve Base in California.

The fallen ARVN soldiers “contributed to the American freedom system,” Cas­tagnetti said. “And since we fought shoulder to shoulder, like I did with them as an adviser in Vietnam, fought shoulder to shoulder with these Vietnamese, they are a brotherhood in military service, and they deserve being properly memorialized and honored and buried with dignity.”

The former Marine recalls three American advisers being assigned to a battalion of about 650 ARVN soldiers when he served in a five- province area around Da Nang.

ARVN soldiers sometimes suffered from low morale and high desertion rates due to poor command and corruption, but Castagnetti said he saw firsthand the determination of the South Vietnamese troops.

“They were dedicated young men,” Castagnetti said. “Our purpose was to give the Republic of South Vietnam its own opportunity for self-governance and freedom from oppression — and they believed in that.”

The soldiers “fought with distinction,” he said.

On Dec. 11, 1965, a U.S. C-123B Provider aircraft failed to return from its mission to deliver the 81 ARVN personnel to Tuy Hoa Airbase. The American crew — Maj. Robert Horsky, Capt. George McKnight, Staff Sgt. Mercedes Salinas and Staff Sgt. Donald Stewart — were presumed dead.

In 1974 South Vietnamese military personnel found the crash site and human remains and turned them over to the U.S. Army Central Identification Laboratory in Thailand. Lab functions were subsequently transferred to Hawaii.

The Air Force crew members were identified in 1979, according to the accounting agency. The South Vietnamese soldiers on board were not manifested by name, however.

Bone fragments and some personal items were collected, with the commingled remains fitting into one large casket, according to Webb.

“The remains from the aircraft were approximately 95% ARVN,” said John Byrd, accounting agency lab director. “We sampled and tested every fragment of bone that could plausibly be one of the Americans on board and have completed all testing. All Americans in the incident have been accounted for.”

Castagnetti and Webb had served together in Vietnam, and both started started working on the burial of the 81 ARVN soldiers in about 2017.

“We had to go through some machinations — like through the California Department of Health … to even get authorization to bring these foreign remains into California for burial,” Castagnetti said.

Webb had to coordinate between the State Department and Department of Defense to get an agreement with the accounting agency in Hawaii to transfer the remains to him as sole legal custodian, Castagnetti added.

Webb said Saturday’s memorialization “will help us remember who we are as Americans, and who we should aspire to be: a people who treasure human life and who will never forget those who stood by us during extraordinarily difficult times.”