MOSUL, Iraq -- The Iraqi informant is a new source, but his tip seems solid: The chief financier of a Mosul terrorist cell, a gas station owner, lives in the neighborhood. He is wealthy enough to afford two armed guards to accompany his son to Mosul University. Now, at 1:13 a.m., under a light drizzle, 25-year-old Lt. Mark Brogan and 13 men from his platoon crouch behind a wall, waiting for the...