Late on the afternoon of Sept. 21, 1969, Marine Lance Cpl. James W. Jackson Jr. of Atlanta walked into a U.S. Navy medical facility in what was then South Vietnam and vanished without a trace. At least that is what the Marine Corps told his family after a rather cursory investigation, a story to which the Corps has steadfastly held for the past 46 years despite the fact that, short of an alien abduction, people just do not simply disappear; there are always explanations. Jackson is among the more than 83,000 American service members and civilian contract workers unaccounted for since World War II. These soldiers of the unreturning army fell on foreign soil and remain there, their last resting places unmarked, their sacrifices for their country often remembered only by those who loved them or served with them.