Duty Recall

In 2003, Major David Allan receives a mysterious green marble from a female soldier. Two months later, he is the only survivor of a shot down C-5 Galaxy over the Iraqi desert. When he wakes up from a three month coma, the year is 1991. History is on course with the way he remembers his past. With prior knowledge of the Oklahoma City bombing and the events of 9/11, is Major Allan capable of altering the future course of history?