The CH-47 Chinook, the workhorse of the US Army, is manufactured by the Boeing Vertol company. The Chinook has served as the prime mover for the US Army and other military forces for decades. Its principal missions include transport of troops, artillery, ammunitions, fuel, water, barrier materials, supplies and equipment on the battlefield. Other missions include medical evacuation, aircraft recovery, fire fighting, parachute drops, heavy construction, civil development, disaster relief, and search and rescue. In the US Army National Guard and among international customers, Chinooks often expend the majority of their flight hours on these latter missions.