Betio, Tarawa Atoll (CNN) -- Archaeologist Gregory Fox is the U.S. military's version of Indiana Jones, but looks more like Jerry Garcia than Harrison Ford.
Fox travels the world digging for his version of treasure -- the remains of missing U.S. service personnel who died in battle.
"One month you're freezing your butt off on a mountain worried about altitude sickness, then you're somewhere wishing you had air conditioning," Fox says, shovel in hand, next to a fresh hole he and a team of Marines are digging in the South Pacific.
"It's basically a promise by the U.S. government that they will do everything in their power to bring their fallen warriors home, and that's the way we roll."
Fox is part of the Joint POW/MIA Accounting Command, or JPAC, a unique team of nearly 400 civilian and military personnel. The unit is two-thirds military and one-third civilian, with each branch of the military represented. While search teams comb the world for remains, specialists back at JPAC headquarters in Honolulu, Hawaii, make matches between bones and soldiers listed as missing in action.
"It's basically CSI, but much slower," Fox says. "We can't make a match in 45 minutes."
Tarawa, a South Pacific atoll, was the site of one the bloodiest battles in Marine Corps history. Starting on the morning of November 20, 1943, more than 1,000 American men were killed in roughly 72 hours of fighting with the Japanese. Hundreds of Marines were gunned down in the water trying to make it to shore.
Tarawa was before Iwo Jima. For Marines, the battle is both a source of pride and a lesson learned. The high casualties were blamed in part to poor planning. The attack was launched during low tide, which left a lot of the landing craft stuck on coral.
The Japanese were sitting in fortified bunkers along the shoreline, shooting Marines at close range as they attempted to make it to the beach. In the end, the Marines took the beach and won the battle. An estimated 4,000 Japanese soldiers died in the fighting, over what was considered at the time a strategic airstrip in the Pacific.
Alexander "Sandy" Bonnyman was posthumously awarded a Congressional Medal of Honor for his heroics at Tarawa.
"I spent my childhood idolizing him, even though he died 18 years before I was born," says his grandson, Clay Bonnyman Evans. Evans made the long trip from his home in Boulder, Colorado, to Tarawa to be here while JPAC is digging for remains.
He retraced his grandfather's steps at Tarawa, wading through the water onshore, then climbing to the top of a bunker referred to as "Bonnyman's Bunker."
Now overgrown and filled with trash, the bunker was a Japanese stronghold during the battle. Bonnyman, according to his fellow Marines, led a charge to the top of the bunker, flushing out more than 100 Japanese soldiers that had been killing Marines on the beach.
"Frankly, most of my life I knew a lot of the story, and I know a lot more now," Evans says from the bunker where his grandfather was ultimately killed.
After the battle, Bonnyman and the other Marines who died were originally buried in several areas around Tarawa. But there were so many bodies, including the thousands of Japanese soldiers, that the U.S. Navy eventually bulldozed the site. After the war, the U.S. government returned to retrieve the bodies, but couldn't find them all.
It's estimated that as many as 450 Marines remain buried on Tarawa. Over the years, several bodies have been unearthed by construction workers and others. On Wednesday, local officials handed over a set of remains to the JPAC team in a ceremony conducted by Marine Capt. Todd Nordman.
Nordman says he volunteered for this mission because of the Marine Corps history here. While JPAC may be made up of all branches of the military, for this mission it's almost all Marines. "Tarawa holds a soft spot in Marine Corps hearts, so it's important that we bring a large contingency from the Marine Corps," he says.
The mission calls for JPAC to dig at six sites, which if the research is correct, could yield more than 100 missing Marines. Finding where to dig took years of research, and several trips to Tarawa with ground-penetrating radar. That work was done by the nonprofit group History Flight and its founder Mark Noah, who has dedicated most of his life over recent years trying to bring the Marines of Tarawa home.
"It's our mission to affect a positive solution to the mystery of what happened to the lost graves of Tarawa," says Noah.
JPAC is using his research as a playbook for the mission. "it was a great first step," says Fox.
The current JPAC mission scheduled to last more than a month. If a mass grave is found, more archaeologists are on standby in Hawaii to come help Fox.