They're known as the "wandering souls", having died in in fierce Vietnam War battles, but now those souls may get to find peace.
Data from Australian military operations has been analysed to tell the Vietnamese government where their fallen soldiers lay, so they can be given a proper burial.
This is particularly important in Vietnamese culture as many believe the spirits of those who died violently, or whose fate is unknown, will wander forever unless the appropriate ceremony is held for them.
University of NSW Canberra lecturer Dr Bob Hall says the analysis of Australian battles and mementos has revealed the location of many Vietnamese soldiers.
"This is the best chance so far since the war ended in 1975 to repatriate the remains of the fallen," he said.
The research will be handed to a Vietnamese delegation at Parliament House on Tuesday, to help the Asian nation find its 300,000 missing war dead.
Operating Wandering Souls began after the Vietnamese government helped return the bodies of six Australians who were listed as missing in action at the end of the Vietnam War.
Since 2012, the project has provided information on more than 450 of those who died in combat with Australian and New Zealand forces and linked their names to specific burial sites.
Researchers have used items such as photographs, diaries and letters taken from Vietnamese soldiers as mementos of war to provide clues to where their owners were buried.