Friday's funeral at Arlington National Cemetery in the US capital honored Benjamin Kopp, 21, an Army Ranger who died at Walter Reed Army Medical Center on July 18.
Kopp, of Rosemount, Minnesota, was wounded on July 10 when his unit came under small arms fire by insurgents in the southern Helmand province, the Defense Department said.
Gates writes personal notes to the families of soldiers killed in the wars in Iraq and Afghanistan and asks his staff to provide photographs and local press clippings.
He reads through the local press "so he could learn more about who they were, and how the community reacted to their loss," Morrell said.
In attending a funeral, Gates tries to do so in "as least a disruptive manner as possible" to keep the focus on the war dead, he said.
Gates has referred to his job of sending young soldiers off to war as a difficult burden.
"The truth of the matter is, being secretary of war in a time of war is a very painful thing," Gates told the CBS network's "60 Minutes" program in May.
"How can you like a job when you go to Walter Reed and you know you sent those young men and women in harm's way?" he asked, referring to the Washington hospital that treats many wounded troops.
"Every single person in combat today I sent there and I never forget that for a second."
Violence has spiked in recent months in Afghanistan amid a US troop buildup. Since the 2001 US-led invasion, more than 700 US soldiers have died in the war, according to Pentagon figures.
In Iraq as of last month, 4,327 American soldiers had died since the 2003 invasion, according to an AFP toll based on the independent website icasualties.org.
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