After more than 40 years of largely unsuccessful attempts to find 300,000 missing war dead, the Vietnamese government in 2014 announced a $25 million project to locate and identify lost soldiers. Although the effort, Project 150, is said to be one of the largest genetic-identification projects ever undertaken, progress remains slow.

Thousands of those missing are lying together in mass, unmarked graves that were dug by U.S. or South Vietnamese forces after battle — graves that have proved elusive despite Vietnam's making "every effort" to find them, said Vietnam People's Army Col. Mai Xuan Chien, who is leading the search for graves in Dong Nai Province, where Bien Hoa Air Base is located.

In addition to the graves still to be discovered, many known burial sites need to be excavated and remains exhumed, said Wolfgang Hoeppner, chief executive of Bioglobe, a German molecular genetics company that — along with the International Commission of Missing Persons — helped to train Vietnamese scientists on DNA-identification techniques.

Once remains are exhumed, scientists will take tooth or bone samples and powder them down to extract DNA, which will then be compared with a database of DNA from living relatives of the missing. Officials hope family members will voluntarily submit samples for that database — once  outreach begins.

Time may be running out.

"The relatives of the victims are dying now," Hoeppner said, "so it's very important to start collecting DNA from family members … or you may have information from the bones, but you won't be able to identify them."

In a country where ancestral worship still plays an important role, many families remain desperate for answers. Some have reportedly paid psychics hefty sums in hopes of finding their loved ones' bodies. In some cases, those psychics have been accused of passing off animal bones as human remains.

Hoeppner said the project, which was originally intended to identify 80,000 remains by 2020, is moving slower than expected in Vietnam. The necessary equipment was purchased by the government and shipped to Vietnam, he said, but it's "still packed up somewhere and unused."