RAMADI, Iraq – He was 5 when he first fired an M-16, his father holding him to brace against the recoil. At 17 he enlisted in the Marine Corps, spurred by the memory of Sept. 11. Now, 21-year-old Galen Wilson has 20 confirmed kills in four months in Iraq – and another 40 shots that probably killed insurgents. One afternoon the lance corporal downed a man hauling a grenade launcher 5½ football fields away. Wilson is the designated marksman in a company of Marines based in downtown Ramadi, watching over what Marines call the most dangerous neighborhood in the most...