Gunship is a generic term for a particular class of
combat aircraft dedicated to the
Close Air Support role. They are designed to be
attack enemy forces very close to the troops they are supporting. They are characterized by a relatively high level of
firepower and
precision. Gunships can be either
fixed wing aircraft or
helicopters.
Close Air Support began during the World War I when fighter pilots began using their fixed machine guns for trench strafing and other attack duties. The biplane fighters of that war were in many ways perfect for the job. They boasted a high endurance and their slow speed meant the aircraft could bring its weapons to bear very precisely. Precision is essential in a good gunship, because without it the risk of friendly fire casualties can negate the aircraft's firepower.
The high attrition inherent in trench warfare led to many innovations as armies struggled to find a way to break the stalemate. In 1918 both the Allies and Germany began experimenting with combined arms techniques. The British Royal Air Force (which was then known as the Royal Flying Corp) was the first to use the technique but it was refined when the Germans attempted using elite troops known as "stormtroopers" to infiltrate and bypass the trench network. Fighter aircraft would strafe and drop small bombs to attack strongpoints while artillery would fire moving barrages to support the stormtroopers.
World War II represented a major development in close air support. Dive bombing represented a major innovation, which was originally developed during the Spanish Civil War by the Luftwaffe. The Junkers JU-87 Stuka is probably the most famous dive bomber By diving down upon a fixed target such as a tank exceptional accuracy could be obtained. The Stuka's accuracy proved devastating during the Nazi Invasion of Poland, and American dive bombers won the Battle of Midway. Ernst Udet even had the plane fitted with a siren to enhance the Stuka's psychological value. However, combat against the British Expiditionary Forces exposed the Stuka's key weakness, one that would be shared by all close air support aircraft, including gunships. As a class they are all extremely vulnerable to anti-aircraft fire, and particularly to fighter aircraft.
Because World War II combat aircraft were almost all propeller driven, they were slow enough and boasted enough endurance to make a good combat air support aircraft, particularly when under the direction of a close air controller. Jet aircraft changed all that, primarily because their speed greatly limited their accuracy as bombers. Although modern aircraft enjoy greatly improved bombing aids, the basic reactions and limitations of the pilot have not changed since the Red Baron. "Iron Bombs" are aimed by precisely timing the bomb's release point. If a pilot has the same sight picture and reactions, the same error will be much greater in an F-4 Phantom moving at 500 MPH than it will be in a P-47 Thunderbolt moving at 200 MPH. That increase in error also increases the safe distance required to protect friendly troops. Pure and simple, a Thunderbolt pilot can shoot enemy troops that are a lot closer to the friendlies than could the same guy in a Phantom. You can see this clearly in the film We Were Soldiers, when an F-100 Super Sabre drops napalm on US positions during close combat. This is one reason the Douglas A-1 Skyraider saw extensive service in Vietnam and is still used by many air forces worldwide.
Both the US Air Force and the US Army recognized the problem at the same time, and each came up with gunships to meet this issue. In Vietnam, US forces faced what were essentially light infantry forces. The North Vietnamese Army was extremely limited in its use of armor and artillery, so it made do with man-portable weapons such as small mortars. Because the NVA recognized the firepower superiority of US troops, who could be supported by both air and artillery, they adopted "bearhug tactics". In other words, they tried to position their troops as close as possible to the US positions in order to deny the US use of those weapons, or at least to ensure friendly fire casualties.
But soldiers love to study history, and the USAF had studied NVA tactics during the French-Indochina campaigns, culminating in the French defeat at Dien Bien Phu. The Air Force began experimenting with gunships during the early 1960's, and built the first AC-47 Spooky in 1964. The ship was simple. They took a C-47 transport plane-- which was nothing more than the military version of the famed DC-3 and armed it with three SUU-11A 7.62 mm "miniguns" with a 6,000 round per minute rate of fire. Gatling Guns. The high rate of fire created a moaning sound that gave the 'spooky' its name. Also tracer rounds in the ammo mix made the weapons appear to be death rays when firing.
The use of a transport aircraft as the basic airframe was brilliant, and set the pattern for all USAF gunships to come. The C-47 could remain aloft for hours, and its roomy hull meant it could load tons of ammunition and a number of parachute flares for night work. It was slow enough to fire accurately, once pilots perfected the "pylon turn" used to bring weapons to bear. The gatling guns brought a terrifying volume of fire, the "one bullet per square inch in a football field" is not out of line. It is reported that no US unit was ever overrun that was under continuous gunship support.
The Army came up with the helicopter gunship. Partly that was a matter of politics. When the Air Force was split off from the Army to form an independent service, control of all fixed wing aircraft passed to the Air Force, with the exception of a few very small planes. The Army does not like being dependent upon another service, which may have its own priorities. They had begun using helicopters during the Korean War. Helicopters of that era were used primarily for medivac and search and rescue duties. The piston engines of that era didn't offer enough power for much more. However, the development of the turboshaft engine liberated the helicopter in terms of untility and lifting power. Turboshafts produce vastly more power and weigh less than their piston equivalents. New helicopters such as the UH-1 Iroquois, or Huey, offered substantial lifting power and much greater performance.
The first Army gunships were simply Hueys, armed with 5.56mm gatling guns and rockets instead of seats. The utility of the design was soon clear. Helicopter gunships offered enormous flexibility in basing, and exceptional accuracy. The first AH-1 Cobra helicopters use almost everything about the Huey except the airframe which has been stripped down to the essentials to permit carrying more ordinance.
Gunships can only be used in a permissive air environment. In air to air combat pilots have a saying, "speed is life". Speed gets you in and out of hostile areas more quickly, and you can use it to maneuver (see energy manueverability). But gunships are slow by necessity. They cannot move too quickly and fire accurately. Thus they are extremely vulnerable to surface to air missiles, or SAMs. Nor can they fly too high, so they are also vulnerable to guns. Fighter pilots consider them "meat on the table". This means you cannot use a gunship, particularly the fixed wing variety, whever extensive air defenses are expected. Helicopters are better, but they must be operated behind the Forward Edge of the Battle Area or FEBA, and must use terrain features to mask themselves.
However, the advantages of gunships greatly outweighs their disadvantages, paticularly in what the Army terms Low-Intensity Conflicts. They have been adopted by many nations, because they have been proven so useful.