The AH-1 Cobra is a two-bladed, single engine attack helicopter manufactured by Bell Helicopter. The AH-1 was the backbone of the United States Army's attack helicopter fleet, but has been replaced by the AH-64 Apache in Army service. The AH-1 twin engine versions remain in service with United States Marine Corps (USMC) as the service's primary attack helicopter. In addition, several surplus AH-1 helicopters have been converted for fighting forest fires. The United States Forest Service refers to their program as the Firewatch Cobra.