By MICHAEL E. RUANE | The Washington Post | Published: April 30, 2021 PHILADELPHIA — Up on deck, where the casket of the unknown soldier was tied down with rope and covered with canvas, the Marine guards lashed themselves to the ship's stanchions so they wouldn't be swept overboard. Twenty-foot seas broke over the pilot house. One Marine was drenched by a wave so big that it tore his hip boots off. And the ship was rolling so badly that the crew feared that each roll would be its last. It was the fall of 1921. The USS Olympia was halfway across the stormy Atlantic, bound from France to the Washington Navy Yard. And the Marine commander realized that if the hallowed casket went over the side, he might as well go, too.