WASHINGTON D.C. (VOA) - They call it rolling thunder - the din created when thousands of high-powered motorcycles fill the streets of Washington for an annual act of remembrance.

The drivers are military veterans - many from the Vietnam War era - accompanied by family and friends.

They converge on Washington every year on Memorial Day weekend to honor their fallen colleagues and to call attention to those still listed as missing in action.

Leaders of the Rolling Thunder event began this year's observance at the White House, where they got an official send-off from President Bush.

"You've done a lot for the country," said President Bush. "The troops appreciate you. The veterans appreciate you. And your president appreciates you."

Mr. Bush will make a formal Memorial Day address Monday at Arlington National Cemetery, just across the Potomac River from Washington.

Smaller scale events are expected in cities and towns across the country on Memorial Day - a holiday that is also seen by many as the start of the summer season in the United States.

America's military leaders say they hope the real meaning of Memorial Day will not be lost this year. Major General Mark Hertling, the commander of multi-national forces in northern Iraq, says at a time when political and economic matters dominate the headlines, Americans run the risk of forgetting the men and women now serving far from home.

"I hope everybody just takes a few minutes on this Memorial Day to just thank a soldier - or more importantly, thank a family member of a soldier, because they are sacrificing just as much," said General Hertling.