Rolling Thunder gathers in U.S. capital for annual 'Ride for Freedom' to honor Memorial Day

A U.S. police officer waves to motorcycle riders during the annual Rolling Thunder motorcycle ride to commemorate Memorial Day in Washington D.C., capital of the United States, on May 27, 2018. Hundreds of thousands of motorcycle riders descended on the nation's capital on Sunday for the 31st annual Rolling Thunder Ride for Freedom to honor Memorial Day. (Xinhua/Yang Chenglin)