"I'm honored to be with you once again as we pay our respects as Americans to those who gave their lives for us all," he told a crowd of military dignitaries, veterans and surviving family members at Arlington National Cemetery.
"Here at Arlington, the deafening sounds of combat have given way to the silence of these sacred hills," Obama said. "The chaos and confusion of battle has yielded perfect, precise rows of peace. The Americans who rest here and their families -- the best of us, those from whom we asked everything -- ask of us today only one thing in return: that we remember them."
The wreath-laying ceremony has become a presidential tradition to honor the more than 1 million members of the military who died while serving their country.
Since last year, Obama said, more than 20 members of the U.S. military were killed in combat in Afghanistan, where the Taliban is seeking to reclaim territory, and another three were killed in fighting in Iraq, where the Islamic State in Iraq and Syria, or ISIS, has made inroads.
After drawing down the number of American troops in Iraq and Afghanistan, the president now oversees U.S.-led military operations in those two countries, as well as Syria. He took time during the ceremony to share stories of the fallen, including Navy SEAL Charles Humphrey Keating IV, who was fatally wounded May 3 in a gunfight with ISIS militants.
"Charles Keating IV, Charlie, Chuck or C4 was born into a family of veterans, all American athletes and olympians, even a gold medalist," Obama said. "So naturally, Charlie and the love of his life Brooke celebrated their anniversary on the Fourth of July.
"She called him the huge goofball everybody wanted to be friends with, the adventurer who surfed and spearfished and planned to sail around the world," he said. "When the Twin Towers fell, he was in high school and he decided to enlist, joined the SEALs because, he told his friends, it was the hardest thing to do.
"He deployed to Afghanistan and three times to Iraq, earning a Bronze Star for Valor and earlier this month, while assisting local forces in Iraq who had come under attack, he gave his life," Obama said.
"A few days later, one of his platoon mates sent Charlie's parents a letter from Iraq. Please tell everyone Chuck saved a lot of lives today, it said. He left us with that big signature smile on his handsome face, as always," Obama said. "Chuck was full of aloha but was also a ferocious warrior. Today, we honor Chief Special Warfare Officer Charles Keating IV."
Obama, who before the ceremony at Arlington held a breakfast reception at the White House for veterans groups and family members of fallen service members, called on Americans to honor those who sacrificed their lives by helping survivors and veterans.
"For the living, those of us who still have a voice, it is our obligation to fill that silence with our love, gratitude and not just our words, but our actions," he said. "We have to do better; our work is never done."
Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, noted more than 40 million people have served in the U.S. armed forces since the nation was founded. Of the more than 1 million killed in action, more than 100,000 died in World War I; more than 400,000 in World War II; almost 40,000 in Korea; more than 50,000 in Vietnam; and more than 5,000 since the Sept. 11, 2001, terrorist attacks, he said.
"These statistics are compelling, but they don't begin to capture the enormity of the sacrifice," Dunford said. "For the loss of each individual brings untold anguish and grief.
"Those statistics represent sons and daughters, brothers and sisters, good friends," he added. "Those statistics represent children who grew up without mothers and fathers. Those statistics represent lives shattered, hopes and dreams never realized.
"Today is a reminder of the real cost of freedom, the real cost of security," Dunford said, "and that's the human cost."