In the United States Army, Army aviation includes those short-range fixed-wing and helicopter aircraft that are integrated into ground units or dedicated to their support, as opposed to long-range aircraft that have missions not associated closely with ground troops. In some other countries, this mission is associated army coordination aircraft.
This is a sensitive issue in the U.S. military, due to a continuing roles-and-mission argument, especially between the Army and the Air Force, dating back to the Key West Agreement of 1948. Written shortly after the Air Force became an independent service in 1947, the Air Force, at first, took responsibility for all armed and long-range aircraft. There was a perception on the part of the Army, however, that the Air Force gave a low priority to ground forces specific missions, such as close air support, forward observers of artillery, battlefield medical evacuation, etc.
As part of the Navy, the United States Marine Corps was not subject to the same restrictions, in part because Naval aviation and Marine aviation saw one another as more complementary than competitive. Since the Marines, on typical assignments, do not have attached medium and heavy artillery or tanks, a Marine air-ground task force (MAGTF) that is task-organized to conduct aviation operations is assumed to have an aviation combat element, responsible for:
|Marine aviation function
|Air Defense Artillery and helicopter self-protection
|offensive air support
|only armed and attack helicopters,
|only armed and attack helicopters,
|helicopter and some specialized aircraft (e.g., Airborne Reconnaissance Low and RC-12 GUARDRAIL
|helicopter and light aircraft
|control of aircraft and missiles
|yes; see ADAM cell
The Marine support, however, can include high-performance aircraft such as the F-18 Hornet.
In the 1920s and 1930s, Army ground forces considered aviation support a critical part of artillery fire adjustment, especially when Air Corps combat aircraft were not available. Light observation aircraft were made organic to artillery units in 1940 and 1941, including the Louisiana Maneuvers. "Grasshoppers", as the Army called them, tended to be slow, for extended observation time, and able to operate from minimal airfields.
World War II
On 6 June 1942 the Secretary of War ordered small single- engine spotter planes to be made organic to artillery units. Eventually this would evolve into the Army Aviation Branch, especially after the air assault experiments of the 1960s.The first units flew L-4 Grasshoppers and a few larger L-5 Sentinels.
Korean War and the development of airmobile foces
Organic Army Aviation had acquired its first helicopters7, shortly before the U.S. Air Force became independent of the Army. In Korea, the value of helicopters became obvious, especially for command and control and medical evacuation.  There was conflict with the Air Force over larger transport helicopters.
A separate Army Aviation School started, at Fort Rucker, Alabama, in 1954. In the following year, the Army Aviation Center was created. The first armed helicopter company was activated in Okinawa in 1962. The Department of Defense did not abolish mission restrictions on the Army's rotary-wing aircraft, and thereby technically authorize the Army to arm helicopters, until 1966. See air assault for the development of a concept, approved by the Department of Defense, which established Army Aviation missions that included armed aircraft.
New doctrines for high-intensity conflict
Army Aviation continued to develop new doctrine, tactics, aircraft, equipment, and organizational structure. New or radically modified aircraft adopted during the early 1980s consisted of the AH-64 Apache, the UH-60 Blackhawk and the OH-58 Kiowa Warrior 
The situation continues to evolve, with unmanned aerial vehicles further confusing the Army and Air Force roles.