An armed helicopter, also known as a helicopter "gunship", has two roles, which can be configured for each operation or mission. One role is to carry troops or cargo to be landed or that will be picked up; and it has various amounts of removable armament to protect combat operations with troops. A second role is purely as an armed helicopter to provide support to combat operations on the ground.
It contrasts with an attack helicopter, which is not designed to carry any troops.
French forces first used, as armed helicopters in combat,the Sikorsky H-19, then being superseded in service by the more capable H-21 and H-34 helicopters. The H-19 was originally fitted with two rocket launchers, and a 20-mm autocannon, both mounted axially on the outside of the aircraft.
Increasingly more potent weapons were added, but the helicopters of the time had insufficient engine power to lift bombs, autocannon, and large rocket pods. Most common was a pair of 12.7mm (.50 caliber) heavy machine guns and a 7.5mm light machine gun.  but this load proved far too heavy, and even more lightly-armed H-19 gunships proved underpowered. Most H-21s in service were eventually fitted with a door-mounted 12.7- or 20-mm gun for self-defense only.
In French Navy service, with no pressure to carry troops, their H-34 variant typically carried a 20mm autocannon, two machine guns, and racks for unguided rockets. While the H-34 was more powerful than the H-21, the H-21 seemed better able to take battle damage.
The Vietnam War saw extensive use of armed helicopters, and limited use of attack helicopters. An "armed" UH-1 helicopter still had door guns, but with more ammunition, possibly dedicated gunner, and occasionally these would be .50 caliber M2 rather than 7.62mm M60. If they were not carrying troops, they might have rocket pods. Such "armed" UH-1 still could carry troops -- but also might have the smaller M178 2.75" rocket pods, and, for a given mission, might or might not carry troops vice more ammunition.
Russia and Afghanistan
Soviet/Russian designers did not follow the U.S. initially in pursuing the development of attack helicopters. They continue to modify their Mi-8 HIP and Mi-24 HIND helicopters with heavier armament. The Mi-24 played a major role in Soviet helicopter operations in Afghanistan.
New roles, and the armed vs. attack role
After Vietnam, and especially into the 1990s, US Army, and some Soviet, attack helicopters were optimized for the antitank mission. This is being reexamined to consider better use of armed and attack helicopters in light infantry and special operations.
Bombing from helicopters
While helicopters have most often used direct fire weapons, with bombs considered more appropriate for fixed-wing aircraft, various specialized bombing configurations have met with varied success. Armed, rather than attack, helicopters lent themselves to use with heavy bombs, as the cargo-handling equipment could be used for the bombs. Attack helicopters did not have the hardware to mount field improvised weapons.
Helicopter bombing in Vietnam
Likely the first organized usage of a helicopter as a tactical bomber, the United States Army employed the UH-1 Iroquois, CH-47 Chinook, and CH-54 Tarhe helicopters. The US Army had already conducted tests using the OH-13 Sioux fitted with small napalm tanks.
The CH-47 was used most often to assist in the clearing of bunkers, using an improvised bomb made from 55-gallon drums of bulk CS powder, designated "Bomb, Fuze, and Burster, CS in 55-gallon Drum, XM920." Thirty of these bombs, containing eighty pounds of CS powder, could be carried by a CH-47, and were used to "saturate base camps, way stations, or infiltration routes to deny their use."
The US Army used the UH-1 with a far wider array of systems. Conventional aircraft dispensers for cluster munitions and mines were fitted. Another system developed was the Mortar Aerial Delivery System or MADS. This system used standard 60mm or 81mm mortar rounds in dispensers mounted on the side of the aircraft, and was to be used against both preplanned targets and targets of opportunity. Pictures show this system in use as late as 1969. Mortar ammunition dropped as bombs is returning in the form of guided mortar shells dropped by unmanned aerial vehicles, with guidance making them immensely more effective than Vietnam-era devices.
Even improvised bombs, made from things such as a "can of engine oil...[and] a thermite grenade" or "four or five concussion grenades...[with] belted M-60 ammunition around the grenades" were used.
The US Army also conducted a number of drops of large bombs using the CH-54 helicopter for the purposes of clearing landing zones. Operational drops were conducted using both modified M121 10,000 lb bombs and the BLU-82 15,000 lb bomb. Tests conducted prior to the deployment of weapons and equipment for Operation Combat Trap led to discontinued use of the CH-54 and a switch to the MC-130 fixed-wing aircraft.
Both the US Army and US Marine Corps also investigated using the AH-1 Cobra as a bomber. The Army tested a dispenser system that could be used to drop smoke grenades, while the USMC went further and qualified the aircraft to carry the CBU-55/A fuel-air explosive optimized for incendiary effect. While the USMC continued to qualify their subsequent AH-1 variants for the CBU-55/A weapon, there are no reports of it actually being used in combat.
Helicopter bombing in El Salvador
During the conflict between the Salvadoran government and the FMLN and other guerrillas between 1980 and 1992, UH-1 helicopters were used as bombers, when more appropriate aircraft were not available. They adapted bombs to use the same mounting hardware as regular rocket racks, which can be jettisoned, so the helicopters needed no modification. 
Helicopter bombing in Lebanon
In 2007, the Lebanese Army technical teams converted UH-1H utility helicopters into bombers due to the urgent need to fight insurgents. They mounted 30-year-old 400 lb (250 kg) Mk.82 bombs, originally used on Hawker Hunter attack aircraft. This was accomplished by modifying the UH-1H helicopters, raising the height of the landing skids and installing belly mounted bomb-release gear and pylons from retired Mirage III jets.
The helicopters dropped 250-kilogram and 400-kilogram bombs from altitudes between 3,000 and 4,000 feet. The pilots used GPS devices to help guide them from point of departure to the bomb-release point. The strikes demolished many of the camp’s two- and three-floor buildings and many of the fortifications of Fatah Al-Islam, according to LAF officials.
Fawzi Abu-Farhat, a retired LAF brigadier general and editor of the monthly Arab Defense Journal, said, "This is the first time in the history of warfare that a helicopter is used as a bomber ... in an effective manner." Abu-Farhat's assertion is not correct as helicopters have been used in the same role and with good success in previous conflicts. He went on to stress that "such helicopter bombs can only be used in special cases, when the enemy does not have air defenses and when the weather conditions are good.  Today, there are all-weather helicopters, but they remain unable to penetrate alert air defenses, as at the First Karbala Raid in the 2003 Iraq War.
Tests and evaluations
Other nations have also made moves toward helicopter bombing, but have not put it into practice. The Soviet Union qualified both the Mil Mi-8 and Mil Mi-24 to use members of the FAB general purpose bomb family. It is possible these aircraft may have been put into service in this role by the armed forces of Sudan and Sri Lanka.
The most common weapons on armed helicopters are machine guns on swivel mounts in the main door or doors. They may also carry small rocket pods carrying 7 or so unguided rockets, and, more recently, may carry light surface-to-air missiles adapted to an air-to-air missile role for self-protection.
Different nations have different design approaches for military helicopters. Russia/the Soviet Union did not emphasize attack helicopters, but their troop-carrying armed helicopters, such as the Mi-8 HIP or Mi-24 HIND are far more heavily armed than the armed helicopters of other countries.
The antisubmarine helicopter has become the key platform that will actually attack an enemy submarine. With the end of the Cold War and the disappearance of a major "blue water" threat from Soviet submarines designed as carrier killers, U.S. naval aviation found that dedicated carrier-based maritime patrol and antisubmarine aircraft, such as the S-3, took up carrier space that could better be used by other aircraft types.
While land-based maritime patrol aircraft such as the British Nimrod, the Russian Tu-142, and the U.S. P-3 Orion and its replacement, the P-8 Poseidon have their roles, the availability of land bases for these aircraft, and the number of carrier decks, is far less than the number of destroyers, cruisers and frigates that can carry a small number of helicopters.
While 2-helicopter capability is most common, Japanese, Italian, and U.S. new designs put hangars on surface combatants that can carry 4 or so helicopters. In a 2-helicopter configuration, there is typically one antisubmarine variant and one special operations helicopter. The Navy has had different variations for basing on carriers versus cruisers & destroyers versus supply ships.
Replacing the sometimes armed, but severely aging H-46 aircraft used by the United States Marine Corps as their primary assault helicopter, and United States Navy H-46s used for transferring supplies, is the MH-60S Knighthawk. The Navy is consolidating several different H-60 variants into the MH-60R Seahawk (ASW and ASuW), and the Knighthawk for troop lift and mine warfare. Both types can be armed; the Seahawk is really an attack helicopter for other than land warfare.
- Tom Cooper (12 Nov 2003), Western and North African Database, Air Combat Information Group
- Mazarella, Mark N (1994). Adequacy of U.S. Army Attack Helicopter Doctrine to Support the Scope of Attack Helicopter Operations in a Multi-Polar World. U.S. Army Command and General Staff College.
- Mutza, Wayne. (1995), H-13 Sioux Mini In Action, Squadron/Signal Publicationsp. 29
- Department of the Army (1969), FM 1-40 Attack Helicopter Gunneryp. K-2
- Rottman, Gordon. (2006), Viet Cong and NVA Tunnels and Fortifications of the Vietnam War, Osprey Publishing p. 46
- Department of the Army (1967), FM 1-100 Army Aviation Utilization p. 12-3
- Drendel, Lou (1983), Huey p. 51
- Drendel, Lou (1974), Gunslingers in Action, Squadron/Signal Publications, p. 20
- Mesko, Jim (1984), Airmobile: The Helicopter War in Vietnam, Squadron/Signal Publications p. 48
- Headquarters, Pacific Air Force, Directorate, Tactical Evaluation, CHECO Division (1970), Commando Vault pp. 1-3
- Mutza, Wayne (2002), Walk Around: AH-1 Cobra, Squadron/Signal Publications pp. 10-1, 34
- Cooper, Tom (3 September 2007), "The victory - Lebanon developed helicopter bombers", Ya Libnan
- Cooper, Tom (29 October 2003), "Sri Lanka, since 1971", Air Combat Information Group