Athletes begin their cycling portion of the Marine Corps Marathon's Quantico Triathlon, Quantico, Va., Aug. 22, 2015. The Triathlon is a three part event consisting of a 750 meter open water swim, 20K cycle tour, and 5K run to complete the entire race. (U.S. Marine Corps photo by Lance Cpl. Elisha N. Peake/Released) - Athletes begin their cycling portion of the Marine Corps Marathon's Quantico Triathlon, Quantico, Va., Aug. 22, 2015. The Triathlon is a three part event consisting of a 750 meter open water swim, 20K cycle tour, and 5K run to complete the entire race. (U.S. Marine Corps photo by Lance Cpl. Elisha N. Peake/Released)