Mercer's unit patrols a dangerous rural area southwest of Baghdad International Airport. Mercer and soldiers in several other Bradleys were driving to an area where insurgents were suspected of planting roadside bombs when the accident took place.
Mercer was slightly hurt by the blast from a roadside bomb the day before he was killed and his regular vehicle was knocked out of service.
Second Lt. Nathan Childers, Mercer's platoon commander, said no one would have faulted the Waycross soldier for declining the second mission, but "That's not the kind of soldier he was. It never would have occurred to him not to go."
Mercer, a hardware store employee in civilian life, won honors as the top noncommissioned officer in the 4,400-member brigade in 2004 for his encyclopedic knowledge of military matters. He served in Bosnia in 2001 and began a yearlong combat tour in Iraq in May.
Mercer is the third member of the brigade to die since the unit was mobilized in January, all in vehicle accidents. One died in training at Fort Stewart in January, and another soldier was killed in Kuwait in May.
Mercer is survived by his wife, Pam, and three children, Alanna, Amber and Gavin.
Childers, 27, of Atlanta said members of Mercer's unit will support his family in the future.
"Pam and the kids are now our family," he said. "We'll look after them from this point forward."
About 300 soldiers attended the outdoor service.
Afterward, they walked individually or in small groups to an elevated stage where they saluted and said final prayers before an upended rifle, helmet, dog tags and combat boots that symbolized the fallen soldier.
"We're all at a loss as to what to do next," Childers said. "His shoes are too big to fill. Everything we do in this country will honor Chad."
"God gave us Chad, and his presence made each of us a better person," said Lt. Col. Harry McCorkle, commander of the 2nd Battalion, 121st Infantry Regiment. "His soldiers respected him because of who he was. They wanted to be like him. His spirit will always be with us."