u.s. forces in iraq were also at the time facing increasing opposition to its previously unchallenged air superiority. insurgent forces were increasingly targeting coalition aircraft, usually american helicopters which provided ample targets. in november 2003, a ch-47 chinook helicopter was shot down near fallujah by a shoulder-fired missile, killing 16 american troops. in 2004, a total of 13 u.s. helicopters were brought down by enemy ground fire over iraq. the increasing prevalence of ground fire led american forces to change their tactics, and helicopters began flying low and predominantly at night to avoid drawing fire.