Clouds are reflected on the Vietnam War Memorial during Veterans Day ceremonies on Nov. 11, 2011, in Washington, D.C.

Capt. Don R. Hood, right-front, and fellow Air Force officers in an A-1 training class at Hurlburt Field, Fla.

Marine Corps veteran Robert Flick looks out from behind a flag during a Veterans Day ceremony at Arlington National Cemetery in Virginia on Nov. 11, 2011.

People arrive at the Amphitheater at Arlington National Cemetery in Arlington, V., Friday, Nov. 11, 2011, for a Veterans Day ceremony where President Barack Obama will speak.

President Barack Obama pauses for a moment after placing a wreath at the Tomb of the Unknowns ad Sgt.1st Class Chad Eric Wayne Stackpole (R), 3rd U.S. Infantry Regiment Sergeant of the Guard, looks on during a Veterans Day full honor ceremony at Arlington National Cemetery November 11, 2011 in Arlington, Virginia. Obama delivered remarks at the cemetery amphitheater after laying the wreath.

Visitors watch in silence as soldiers from the 3rd U.S. Infantry Regiment, called the "Old Guard," perform the changing of the guard at the Tomb of the Unknowns before a Veterans Day full honor ceremony at Arlington National Cemetery on Nov, 11, 2011 in Arlington, Virginia.

Visitors listen during a Veterans Day ceremony at Arlington National Cemetery in Virginia on Nov. 11, 2011.

World War One reenactors with a U.S. Army division march in the Veterans Day Parade on Nov. 11, in New York City. The New York Veterans Day Parade includes active-duty officers, veteran's groups, junior ROTC members, and the families of veterans. The parade, which has been held in New York since 1929, features over 25,000 participants, making it the largest Veterans Day Parade in the nation.

Soldiers wait to march in the Veterans Day Parade in New York City, Nov. 11, 2011. Veteran's Day was originally held to commemorate the end of World War I, but has since become a holiday to recognize soldiers' sacrifices for the United States.

West Point cadets prepare to march in the Veterans Day Parade on Nov. 11, 2011 in New York City. The New York Veterans Day Parade includes active officers, veteran's groups, junior ROTC members, and the families of veterans. The parade, which has been held in New York since 1929, features over 25,000 participants, making it the largest Veterans Day Parade in the nation.

Employees of the insurance company Lloyd's of London observe a two minute silence on Armistice Day in the Underwriting Room of the Lloyd's Building in London on November 11. The annual Remembrance Day service honors those who have lost their lives during times of war. The service at Lloyd's is observed with the ringing of the Lutine Bell, the laying of wreaths before the Book of Remembrance and a two minute silence.

Veterans attend Commando Memorial at Spean Bridge in the Highlands of Scotland to observe a two minute silence as a mark of respect for the war dead on November 11, Scotland. Armistice Day traditionally marks the end of WWI when Germany and the allied forces signed the armistice signaling the end of hostilities on the Western Front. The cessation of the war officially took effect on the eleventh hour of the eleventh day of the eleventh month and is marked annually by services of remembrance for all those who have fallen in wars and a two minute silence.

Artist Ted Harrison pictured with his art installation at St Paul's Cathedral in London on November 11. Harrison used more than 5,000 poppies to create an image of three child soldiers from the First World War and more recent conflicts.

This Eugene Smith picture -- of Marines taking cover on an Iwo Jima hillside as a Japanese bunker is obliterated -- captures the cataclysmic destruction inherent in war perhaps more perfectly than any other single image ever published in LIFE.

This starkly gorgeous Larry Burrows photo, taken in Khe Sanh, laid bare the vulnerability of our troops, who were facing what was shaping up to be the biggest battle of the Vietnam War. Six thousand Marines were dug in at the isolated plateau -- a fraction of the 40,000-man force steadily advancing upon them. The ammunition and supplies being delivered by this 1st Air Cavalry Skycrane helicopter were badly needed. But the unanswered question seems to hang in the air with the chopper: Will it be enough?

Amos Cortez, who fought in the Vietnam War with the U.S. Army in 1966, reacts as he finds the name of one of his five high school friends who were killed in the war, on a travelling version of the Vietnam Memorial at the Welk Resort Theater in Branson, Missouri on Wednesday, Nov. 9.

A group of volunteers packing artificial poppies for Armistice Day in an undated photo.

Earl Haig (1861 - 1928) watches the stamping of poppies by ex-servicemen during a visit to the British Legion poppy factory on October 22, 1926 in Richmond, Surrey, England. Haig, who commanded British forces during the Battle of the Somme, was a leading light in the spread of the poppy day appeal.

Fourth-grade teacher Becky Luckett wipes away tears, Nov. 5, 2010, during West Louisville Elementary School's ninth annual Veterans Day celebration in West Louisville, Ky. She left the gym during a documentary interview with World War II veteran William Brey. "We don't realize what these men have gone through," Luckett said.