First to Fight — Christopher G. Nuttall

Before Avalon, before the Fall of the Empire, Edward Stalker was a young man growing up in Earth's Undercity - a nightmarish rabbit warren of tiny apartments dominated by gangs who loot, rape and murder with impunity. When his family is killed in a gang attack, Ed takes the opportunity to run to the one place that will take him; the Terran Marine Corps. But becoming a Marine isn't easy and Ed will find himself pushed to the limits, surviving a training program designed to weed out everyone but the best, before he learns what it means to be a Terran Marine ...