U.S. Army soldiers of the 3rd United States Infantry Regiment arrive to place U.S. flags on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

U.S. Army soldiers of the 3rd United States Infantry Regiment arrive to place U.S. flags on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

U.S. Army soldiers of the 3rd United States Infantry Regiment place U.S. flags on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

U.S. flags placed on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

U.S. Army soldiers of the 3rd United States Infantry Regiment place U.S. flags on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

A U.S. Army soldier of the 3rd United States Infantry Regiment places U.S. flags on graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

Flags decorate graves at Arlington National Cemetery in advance of Memorial Day in Arlington, Va., May 24, 2018.

Workers unload some of the 66 Eternal Reef balls with plaques representing each of the submarines and crewmembers lost at sea since 1900, which will be deployed to the ocean floor during a ceremony this Memorial Day weekend off the coast of Sarasota, Fla., May 23, 2018. 

Some of the 66 Eternal Reef balls with plaques representing each of the submarines and crewmembers lost at sea since 1900. 

The USS Kete submarine was lost as its transited to Midway Island after torpedoing three Japanese ships while on patrol in May 1942. Eighty-seven lives were lost.

People are reflected on a temporary memorial made of more than 600,000 poppies, erected at the National Mall in Washington, D.C., ahead of Memorial Day, May 25, 2018.