It was supposed to be a routine resupply mission: a short drive across the Al Asad Air Base, 90 kilometers north of sweltering Baghdad, to fetch, among other things, a newly-arrived TV to entertain the troops. Jimmy Castellanos, a 20-year-old Marine just five months into his first tour in Iraq, was supposed to be riding on the convoy. But on the afternoon of March 18, 2004 Castellanos, who worked maintaining the weapon systems of the U.S. Army’s Cobra attack helicopters, was told that he was needed for guard duty. His friend and bunkmate took his place.