They're rolling, and it is indeed thunderous - driven by heartfelt patriotism and Old Glory, flapping on the back of a Harley somewhere on the Capital Beltway.
Hear that? Rolling Thunder has arrived.
For the 22nd year, the capital of the free world will reverberate with the thudding of thousands and thousands of motorcyclists, all of them united by a single message.
"Never forget all of our prisoners of war and those still missing in action from all wars, and never forget our veterans of all wars. That's our message, and that's our mission," said former U.S. Army Sgt. Artie Muller, founder of the group that 14 years ago took its name from a combat operation.
"Operation Rolling Thunder" was the U.S. military code name for the intense, long-term bombing of North Vietnamese targets in the mid-1960s.
"We're here to remember and honor our POWs, our MIAs and our vets, and to remind Washington that government inaction on issues of importance to them is terrible. It's personally very, very aggravating to me," Mr. Muller said.
"God bless Artie. God bless all of them for coming out and riding for those who can't," said singer Nancy Sinatra, who will accompany the group through the streets of Washington Sunday and later perform with the U.S. Army Band.
She took a USO tour of Vietnam in 1967 and never forgot what she saw in the days when her hits "These Boots are Made for Walkin' " and "Sugar Town" were topping the music charts.
"I saw so many faces from those stages. I wondered who made it back and worried about those who didn't. I just had to find some way to show my respect for all these heroes, to connect with them. And Rolling Thunder is it. It's really a spiritual experience," Miss Sinatra said.
Her own memories come into play as well.
"I've been to the vets hospitals, I've looked into the eyes of people who've been to war and met with children who never knew a father killed long ago. It hurts my heart sometimes," Miss Sinatra said. "The most important thing you can do if you meet a veteran from any war is to just listen."
Rolling Thunder is a nonprofit group, not a motorcycle club, and is run entirely by volunteers in 88 chapters across the nation. The organization maintains a separate fundraising arm and stages raffles and public events to raise money for ailing veterans and the families of injured soldiers who need help with medical bills or transportation to distant hospitals.
The group has financed expeditions to recover remains in Vietnam, North Korea and elsewhere. Volunteers send packages to troops overseas and visit schools, rehabilitation centers and senior citizen homes with messages about patriotism and loyalty.
A number of issues continue to galvanize the membership.
The members insist that the United States continue to search for any live prisoners of war (POWs) or service members missing in action (MIAs). They are troubled by the Defense Department's "aggressive practice" of discharging military personnel for pre-existing personality disorders and are vexed by a recent Department of Homeland Security document on "right-wing extremism" that suggested that disgruntled military veterans be placed on a watch list.
Veterans' medical care and the challenges that veterans face when navigating the federal system concern the group.
"No big officials want to push themselves out in the limelight to do anything about these problems," Mr. Muller said. "Where is the White House? Where are the politicians? Where is House Speaker Nancy Pelosi? They've got to remember that war is hell, and our troops deserve the best."
Still, the wheels beckon and his signature black beret is ready. Mr. Muller will lead the motorcycle multitude aboard a 1992 Harley Davidson "low rider" with a flawless black finish, flame orange pinstripes and polished chrome.
His riding mates could number 850,000 this year from every state, he said, along with Canada, Europe and Australia and other far-flung places. They'll barrel forward on big bikes and small, on "old-school" choppers, high-tech sport bikes, grand three-wheelers or maybe a full-dressed Harley with a sidecar - perfect for a man and his missus.
"No attitudes. Confirmed: everyone must wear a helmet," notes a directive to the participants, who will assemble at the Pentagon parking lot early Sunday morning for the big ride. It takes about four hours to send the bikers out in waves - over the Memorial Bridge to the Vietnam Veterans Memorial.
Although the massive ride is the real mission, the weekend also will include a candlelight vigil, memorial wreath presentations, musical tributes, color guards and a free barbecue - all events punctuated by the saying of the Pledge of Allegiance and a rousing chorus of the national anthem.
"Our motto is 'we will not forget.' And I don't think we ever will," Mr. Muller said.