The helicopter has emerged as an important addition to air power and the conduct of military operations since the end of WW II, and has become crucial to modern-day armed forces. It offers tremendous flexibility and mobility to troops and has been particularly useful in low-intensity operations and in providing support to units operating in dense terrain or terrain accessible only with great difficulty. The helicopter's ability to operate from hastily prepared clearings or in rugged country which would otherwise preclude the use of direct air support has been its greatest asset, although the helicopter has been deployed in a wide variety of roles for which its particular attributes make it well suited.
Although the helicopter has only come to prominence since the early 1950s, its gestation dates back to the time of the earliest fixed-wing powered flights. However, slow development has largely been due to the many and varied problems inherent in the helicopter's basic design. Compared to a fixed-wing aircraft, the helicopter is a much more complex piece of equipment in two basic ways. First, a sophisticated and precise transmission system is necessary, while secondly, the rotor blades have to be capable of operating effectively and safely over a wide range of speeds, as the central parts of the rotor move at relatively slow speeds while those nearer the tips move at near sonic speeds. Flawed rotor-blade design could result in aerodynamic vibrations as they travelled through the air, resulting in aerial buffeting, while an inadequate transmission would cause mechanical vibrations. These problems of design and engineering proved insurmountable for many decades, despite the fact that many of the mechanical hurdles were quickly identified.
Early efforts date back to the years leading up to WW I, but little lasting progress was made. Real breakthroughs came about in the inter-war era as a result of advances in mechanical engineering and aerodynamics, but the most basic problem confronting helicopter designers was the torque reaction. A single-powered rotor causes the body of the helicopter to turn in the opposite direction—this being the torque reaction. Much of the development between the wars was intended to solve this problem by having a second rotor which turned the opposite way, thus cancelling the torque effect. In France, Italy, and the USSR a number of multi-rotor helicopters were tested with limited and varying degrees of success. In France the control system developed by the Marquis de Pescara, an Argentine, proved highly successful and is now almost universally employed in modern helicopters. However, most designs still had two or more contra-rotating blades to solve the torque problem and this caused highly complex and unsound craft. There were also problems of engine-cooling and power-handling ratios.
More progress was made in the inter-war era in the development of the autogiro, which had an unpowered overhead rotor blade driven by the airflow from a conventional tractor propeller in the nose. Aside from an initial starting rotation the rotors were driven by the airflow only, and thus they autorotated. The main advantage of the autogiro was that it solved the torque reaction problem, but a failing was the need for a short take-off run—it could not lift off vertically, nor indeed hover effectively. Juan de la Cierva in particular pioneered the development of the autogiro, and much valuable information was gathered that was later fed into the design of the helicopter.
The first moderately successful helicopter design was the Breguet 314 of the mid-1930s, a model which incorporated a rotor-blade cyclic pitch system to tilt the rotor in flight, linked with collective pitch change for vertical control. This was followed by the Focke-Achgelis Fa61, still a contra-rotating design, but one which in 1938 was able to perform controlled hovering flight in the hands of a skilled pilot. During the war a tiny number of helicopters and autogiros were employed, sometimes actually seeing action, though success was sporadic at best.
However, the major breakthrough was spearheaded by Igor Sikorsky in the USA who was the first designer to conquer the torque problem. In 1940 his VS-300 design used a long tail boom with a small vertical rotor to counter the torque reaction. It was not a new idea but the system, now almost universally employed by helicopters, proved remarkably successful. Further development followed and by the closing stages of the war Sikorsky had orders from the US army and the Royal Navy. In the immediate post-war years the interest in the potential military and civil applications of helicopters caused a burgeoning of manufacture and design. By 1947 there were over 70 helicopter projects in the USA and companies such as Westland, Cierva, Saunders-Roe, Bristol, and Fairey in the UK all moved into the field. Similar interest was demonstrated in France, Italy, Germany, and the USSR.
During the mid-1950s a further major developmental step was taken when turboshaft engines began to be integrated into helicopter designs. Hitherto, helicopters had been powered by piston engines and this had brought many cooling problems. When turbo-engines became compact enough to be used in helicopters many benefits followed. Cooling problems were eased, more powerful engines could be used, and high power use, for hovering and lifting over long periods, was greatly facilitated.
The Korean war also acted as a great boost to development. The war demonstrated the capability of the helicopter, first in operations to rescue and recover downed Allied aircrew, but additionally in the tactical movement of troops to enemy rear zones. With new and more powerful helicopters being designed and produced, the age of the helicopter was at hand. The Vietnam war saw the helicopter truly come into its own, and it was deployed on a wide scale, undoubtedly the largest to date. Apart from US army formations, the USAF, the US Navy, and the US Marine Corps all employed helicopters in a variety of roles. In addition, the CIA-sponsored Air America had its own helicopter fleet employed on extra-theatre operations in Cambodia and Laos, demonstrating the helicopter's value in covert operations.
The USSR also employed large numbers of helicopters in the Afghanistan war to some effect. However, certain problems started to emerge. Helicopters were naturally vulnerable to fixed-wing enemy aircraft, and thus air supremacy or certainly air superiority was an essential prerequisite. However, little could be done about increasingly sophisticated ground-based anti-aircraft capability, notably surface-to-air missiles such as Stinger and Blowpipe. Helicopters employed defensive tactics such as NOE (nap of the earth) flying to minimize risk, but as with all types of battlefield air support, effectiveness decreases markedly in a hostile operating environment.
Nevertheless, the potential of the helicopter was clear and irrefutable. A whole host of helicopter designations and uses began to be formulated. For army support the helicopter is essentially now deployed in four basic roles. Observation helicopters (OH) are generally unarmed, small, fast, and manoeuvrable, and tasked with scouting and reconnaissance duties. Versions have included the Coyote, Iowa, Sioux, Scout, and Gazelle. Attack helicopters (AH) are specifically designed for ground attack (see fighter) and close air support (CAS) operations. They are often armoured, present limited frontal profiles and silhouettes, and are armed with a variety of weapons such as cannon, rockets, machine guns, and technologically advanced missiles. Versions include the AH-1 Cobra, AH-64 Apache, and now the AH-64D Longbow Apache. The utility helicopter (UH) is the basic multi-purpose workhorse model, and is capable of carrying a squad or section of well-equipped troops or stores and supplies and if they are armed at all it is with door-guns. Versions include the Huey, Blackhawk, Lynx, and Puma. Cargo helicopters (CH) are heavier models capable of carrying 60 troops, lightly armoured vehicles, or underslung loads such as artillery and munitions. Types include the CH-46 Chinook and the CH-53.
Large-scale airmobile assaults can now employ all four types of helicopters, OHs to scout and reconnoitre ahead, gathering information and selecting targets for AHs. The AHs protect the main force from ground threat, prepare the landing zones, and provide close fire support for the landings themselves. UHs bring in the troops to secure the landing zones, take in cut-off forces for sweeps, prior to the main force being brought in by the CHs. This could include troops, artillery (or local fire support and air-defence), stores (offensive and defensive), and air-portable vehicles.
Most major world powers have formations based on the above aircraft, usually at brigade level. The US army pioneered the model with the 1st Air Cavalry in Vietnam, and then continued with the development of the 101st Airmobile Division and to a lesser degree the 82nd Airborne Division (also parachute-trained). What is clear is that helicopter-borne formations tend to be taking over from paratroop forces and airborne or parachute units are training for the airmobile role.
Other powers have developed similar forces, though naturally on a more limited scale. The British have the 24th Airmobile Brigade with limited non-integral lift capability, the French the 4ème Division Aéromobile, and Germany the Luftlandebrigade with paratroops, airmobile infantry, and anti-armour Fallschirmpanzerabwehr battalions.
In an offensive CAS role the helicopter certainly proved its worth in the Gulf war, most famously with the AH-64A Apache attacks on the fleeing Iraqi troops on the Basra road. Again the caveat that air supremacy was assured throughout should be borne in mind when considering the true combat effectiveness of helicopters. In operations when air superiority might be contested or when ground-based AA fire could be sophisticated or intense, the helicopter would encounter serious tactical problems.
Nevertheless, the latest developments seem to be pushing the helicopter's CAS capability to new heights. The new AH-64D Longbow Apache is the latest leap forward, with claims being made that while a battalion of AH-64As could destroy an armoured regiment, a Longbow Apache (64D) battalion could wipe out a division. Stand-off capability where aircraft can loose off missiles from 2, 187-3, 281 yards (2, 000-3, 000 metres) from a target is nothing new and along with fire-and-forget ordnance have offered CAS huge advantages, but perhaps more importantly the Longbow is designed for 21st-century digital warfare. Longbows will be co-ordinated such that they will hunt over wide areas, three helicopters covering a 3.1 mile (5 km) front, for example. Any gathered information will be digitally disseminated to other Longbows which will then move into the most advantageous positions to prosecute the attack. The Longbow carries up to sixteen Hellfire anti-armour missiles which can independently seek out targets once located, along with 30 mm cannon and Hydra missiles. The US army has focused training in the 21st Cavalry Brigade to develop the sophisticated tactics and operational concepts required to maximize the Longbow's potential.
Helicopters have also been enthusiastically adopted by world navies. The helicopter provides an excellent platform for many maritime duties, especially anti-submarine operations. The helicopter can carry out the duties of a surface anti-submarine vessel by carrying underwater detection equipment and appropriate ordnance to deal with the threat once located. Helicopters can significantly extend the anti-submarine capability of a surface force at much smaller cost and risk than a surface vessel. They can also be used for ferrying personnel between ships or to shore and for air-sea rescue duties. The Sikorsky Sea King helicopter was specifically designed for anti-submarine operations and has become commonplace in the world's navies. It has been built under licence in Britain, Italy, and Japan, all by home-based firms and with minor modifications.
The impact of the helicopter on the conduct of military operations has been highly significant therefore, shaping capability in many ways from airlift, to ground support, to maritime duties. The inherent flexibility of the helicopter principle continues to play an important part in determining the nature of force structures in the future, and in the varied and complicated post- Cold War environment the helicopter is an ideal tool.
Bibliography
- Fay, John, The Helicopter (London, 1987).
- Mason, Tony, Airpower: A Centennial Appraisal (London, 1994).
- Ripley, Tim, Modern Military Helicopters (London, 1998)
— John Buckley
