Under bright, hazy skies at Arlington National Cemetery, President Obama spent his fourth  Memorial Day as commander in chief honoring the hundreds of thousands of  soldiers who died serving their country, particularly  in the Vietnam War, which began more than 50 years ago.

"From the jungles of Vietnam to the mountains of Afghanistan, they stepped forward and answered the call," Obama told hundreds gathered in the humid, midday heat at the cemetery,  which is across the Potomac River from the capital.

 "They fought for a home they might never return to; they fought for buddies they'll never forget. While their stories may be separated by hundreds of years and thousands of miles, they rest here, together. Side by side, row by row.  Because each of them loved this country and everything it stands for more than life itself."

Heeding to custom, Obama also laid a wreath at the Tomb of the Unknown Soldier, pausing to reflect and pray as  a lone bugler played taps.

Obama took pains to point out that "for the first time in nine years Americans are not fighting and dying in Iraq."

That declaration drew applause, as did his pronouncement that "we are winding down the war in Afghanistan and our troops will continue to come home.

"After a decade under the dark cloud of war, we can see the light of a new day on the horizon," Obama said, pointing out that  we need to remember not only the fallen but their families  too.

"As a country, all of us can and should ask ourselves how we can help you shoulder a burden that nobody should have to bear alone," he said.

"Sending our troops into harm's way is the most wrenching decision that I have to make," Obama said. "I can promise you that I will never do so unless absolutely necessary, and that when we do we must give our troops a clear mission and full support of a grateful nation."

The White House announced last week that the Vietnam Veterans Memorial Fund, the National Park Service and the Department of Defense had launched a 13-year program to "to honor and give thanks to a generation of proud Americans who saw our country through one of the most challenging missions we have ever faced."

It was 50 years ago in January that the U.S. began to provide helicopter support to the South Vietnamese. That action grew into a 13-year conflict that took more than 58,000 American  lives.

Obama and Vice President Joe Biden will visit the Vietnam War Memorial later today to  pay further tribute.