WASHINGTON, District of Columbia - They may no longer be in military uniform but nearly all of them are sporting the same thing - leather vests covered with multicolored military patches.Who are they? Tens of thousands of US veterans and supporters who take part in Rolling Thunder, an annual motorcycle rally in the nation's capital to remember the fallen and prisoners-of-war.Each year the veterans ride through the streets of Washington, past the majestic monuments along the national Mall and the hallowed halls of Capitol Hill to ask the government to keep working to find those left behind.FOR POWs and MIAsBill Driscoll, sporting the ubiquitous leather vest and many tattoos as he watched bikers cruise by under a blistering sun that reflected off their motorcycles, said: "This is the heart of America. That's what we're all about. They're riding from California, from Wisconsin, from all over the States."It's a tribute to all veterans. I didn't go to 'Nam. A bunch of my buddies were there. Lots of them passed away."Rolling Thunder was first held in 1988 when a group of bikers, each a Vietnam veteran, decided to ride in Washington every year on or about the Memorial Day holiday to demand the return of the remains of PoWs and those missing in action (MiAs).The name refers to Operation Rolling Thunder, an aerial bombardment campaign launched against North Vietnam by then US president Lyndon B Johnson in 1965.There are an estimated 1500 PoWs and MiAs from the Vietnam war whose remains were never recovered.Over time, the Rolling Thunder parade has become a boisterous display of unabashed patriotism and a tribute to veterans of all foreign wars. Along Constitution Avenue, one of the US capital's main thoroughfares, bikers ride for hours astride their motorcycles, some with sidecars and almost all Harley-Davidsons.NO AGE RESTRICTIONSMany of them fly the red, white and blue of the American flag, or the black PoW/MiA banner that reads: "You are not forgotten." Some carry backpacks, others have coolers. One even had a trailer hitched to his ride.With a cigar in his mouth, a beret on his head, two diamond-like studs in his left ear, and sporting a camouflage jacket adorned with medals and badges, Elton Ensor says he must be "probably one of the oldest to be here today".The 87-year-old Ensor - who fought on the beaches of Normandy during World War II, in the Korean war and in Vietnam - says he has no illusions about the realistic prospects for seeing the remains of his comrades-in-arms returned."They're doing their best, I guess," Ensor said of the Obama administration.