War

3.10 Military aircraft

• 3.10.1 EARLY HISTORY
• 3.10.2 WORLD WAR I
  • 3.10.2.1 Airships.
  • 3.10.2.2 Reconnaissance aircraft.
  • 3.10.2.3 Fighters.
  • 3.10.2.4 Ground attack.
  • 3.10.2.5 Ground attack.
  • 3.10.2.6 Naval aviation.
  • 3.10.2.7 Air transport and training.
• 3.10.3 INTERWAR DEVELOPMENTS
  • 3.10.3.1 Civilian design improvements.
  • 3.10.3.2 Fighters.
  • 3.10.3.3 Bombers.
  • 3.10.3.4 Carrier aircraft.
• 3.10.4 WORLD WAR II
  • 3.10.4.1 Fighters.
    • 3.10.4.1.1 Day fighters.
    • 3.10.4.1.2 Night fighters.
  • 3.10.4.2 Ground attack.
  • 3.10.4.3 Bombers.
  • 3.10.4.4 Naval aviation.
  • 3.10.4.5 Reconnaissance.
  • 3.10.4.6 Training.
  • 3.10.4.7 Air transport.
  • 3.10.4.8 Helicopters.
• 3.10.5 THE JET AGE
  • 3.10.5.1 Early jet fighters.
    • 3.10.5.1.1 Subsonic flight.
    • 3.10.5.1.2 Transonic flight.
  • 3.10.5.2 Modern jet fighters.
    • 3.10.5.2.1 Supersonic flight.
    • 3.10.5.2.2 Mach 2.
    • 3.10.5.2.3 Multimission.
  • 3.10.5.3 Bombers.
    • 3.10.5.3.1 High-altitude craft.
    • 3.10.5.3.2 Low-level penetration.
  • 3.10.5.4 Stealth.
    • 3.10.5.4.1 The first operational craft.
    • 3.10.5.4.2 Stealth technology.
  • 3.10.5.5 Other military aircraft.
    • 3.10.5.5.1 Transport.
    • 3.10.5.5.2 Reconnaissance.
    • 3.10.5.5.3 Airborne early warning.
  • 3.10.5.6 Helicopters.
    • 3.10.5.6.1 Assault and attack helicopters.
    • 3.10.5.6.2 Naval helicopters.
  • 3.10.5.7 Remotely piloted vehicles.

Aircraft have been a fundamental part of military power since the mid-20th century. Generally speaking, all military aircraft fall into one of the following categories: fighters, which secure control of essential airspaces by driving off or destroying enemy aircraft; bombers, which are larger, heavier, and less maneuverable craft designed to attack surface targets with bombs or missiles; ground-support, or attack, aircraft, which operate at lower altitudes than bombers and air-superiority fighters and attack tanks, troop formations, and other ground targets; transport and cargo planes, big-bodied craft with large amounts of interior space for carrying weapons, equipment, supplies, and troops over moderate or long distances; and helicopters, which are rotary-winged aircraft used for ground support, to transport assault troops, and for short-distance transport and surveillance. (see also attack aircraft, fighter aircraft )

3.10.1 EARLY HISTORY

When the first practical aircraft were produced, in the form of hot-air and hydrogen balloons in 1783, they were adopted quickly for military duties. In 1793 the French Convention authorized formation of a military tethered-balloon organization, and a company of "Aérostiers" was formed on April 2, 1794. Two months later the first military reconnaissance from such a balloon was made before the city of Maubeuge. Until the Aérostiers were disbanded in 1799, their reports contributed to the success of French armies in many battles and sieges. Similar reconnaissance balloons were used later by other armies, notably by both armies during the American Civil War and by the British in Africa from 1884 to 1901.

True military aviation began with the perfection of the navigable airship in the late 19th century and the airplane in the first decade of the 20th century. The brothers Wilbur and Orville Wright, who made the first powered, sustained, and controlled flights in an airplane on Dec. 17, 1903, believed such an aircraft would be useful mainly for military reconnaissance. When they received the first contract for a military airplane from the U.S. government in February 1908, it called for an aircraft capable of carrying two persons at a speed of at least 40 miles (64 kilometres) per hour for a distance of 125 miles. The aircraft they delivered in June 1909 was listed as "Airplane No. 1, Heavier-than-air Division, United States aerial fleet."

The most formidable aircraft of the years before World War I were airships rather than airplanes. Airships were large, self-propelled craft usually consisting of a rigid, fabric-covered metal frame within which were gas bags containing a lighter-than-air gas such as hydrogen. The most ambitious examples of this type of craft were the huge airships designed and built in Germany by Ferdinand, Count von Zeppelin. A typical zeppelin could carry five 110-pound (50-kilogram) high-explosive bombs and 20 6.5-pound incendiary bombs at a time when most military airplanes were without any form of weapons, being intended only for reconnaissance.

Experiments with arming airplanes were made spasmodically after 1910, when August Euler took out a German patent on a machine-gun installation. Bombing techniques evolved simultaneously. Dummy bombs were dropped on a target in the form of a ship by the American designer Glenn Curtiss on June 30, 1910. This test was followed by the dropping of a real bomb and the devising of the first bombsight. In England the Royal Flying Corps (RFC) fitted some of its aircraft with bomb carriers, which consisted of a kind of pipe rack beside the observer's cockpit in which small bombs were retained by a pin. The pin was pulled out over the target by tugging on a string. It was primitive but it worked. The Naval Wing of the RFC subsequently attempted to drop torpedoes from Short and Sopwith seaplanes, with some success, and efforts were soon under way to develop means to launch and recover such craft on shipboard. In 1910-11 a Curtiss biplane had been flown from and onto wooden platforms erected over the decks of anchored U.S. Navy cruisers, and in May 1912 a pilot of the Naval Wing, RFC, flew a Short S.27 biplane from HMS Hibernia while the ship was steaming at 10.5 knots. The following year the old cruiser Hermes was fitted with a short deck from which seaplanes took off on wheeled trolleys that were fitted under their floats and dropped away as the machines became airborne.

Thus, by 1914, reconnaissance, bomber, and carrier-based aircraft all were evolving, and some had been used in combat. The first use of an airplane in war was on Oct. 23, 1911, during the Italo-Turkish War, when an Italian pilot made a one-hour reconnaissance flight over enemy positions near Tripoli, Libya, in a Blériot XI monoplane. The first bombing raid came nine days later, when a pilot dropped four grenades on Turkish positions. The first reconnaissance photographs of enemy positions were taken on Feb. 24-25, 1912, in the same conflict.

3.10.2 WORLD WAR I

3.10.2.1 Airships.

At the start of the war the German armed forces had 10 zeppelins and three smaller airships, but this impressive offensive capability was largely offset by the highly explosive nature of the hydrogen gas that gave the zeppelins their lifting power. After losing three zeppelins in daylight raids over heavily defended areas in the first month of the war, the army abandoned airship operations, but the navy, with its battle fleet blockaded in port by the Royal Navy, mounted a night bombing offensive--the first aerial strategic bombardment campaign in history. (see also United Kingdom)

The finest of the zeppelins was the LZ-70; this craft was 740 feet (220 metres) long, was able to fly above 16,000 feet, and had a range of 7,500 miles. The LZ-70 was shot down late in the war, however, and large rigid (metal-framed) airships were never again employed as combat aircraft. Smaller, nonrigid airships were used throughout World War I by the British for antisubmarine patrol, convoy escort, and coastal reconnaissance, achieving a remarkable record of protecting coastal convoys from German submarines. They were revived by the U.S. Navy during World War II for the same use.

Unpowered, captive balloons also were used extensively for observation and artillery spotting in World War I, but by World War II they had become so vulnerable that they were used only as unmanned antiaircraft barrage balloons. Anchored to the ground or ships by cables, they compelled attacking enemy aircraft to fly high to avoid the cables; they also brought down many German pilotless V-1 "buzz bombs" over England in 1944-45.

3.10.2.2 Reconnaissance aircraft.

At the outbreak of World War I, heavier-than-air craft were used only for visual reconnaissance, since their feeble engines could carry little more than a pilot and, in some cases, an observer aloft. They soon proved their worth in this mission, however, and RFC aviators provided reconnaissance that enabled the British and French armies to counterattack in the decisive Battle of the Marne on Sept. 6-12, 1914, turning back the invading Germans just short of Paris.

More powerful engines and better aircraft designs soon made possible specialized reconnaissance aircraft that could fly at high altitudes to avoid interception. The Germans, for example, had Rumpler two-seaters in service by 1917 that could operate as high as 24,000 feet. Radios were carried aloft to permit aerial observers to spot and adjust artillery fire, at first with transmitters only and then, as radios became lighter, with receivers for two-way communication.

3.10.2.3 Fighters.

The importance of aerial reconnaissance and artillery spotting (particularly the latter) made it clear that the belligerent able to deny the enemy use of airspaces above the battlefield would enjoy enormous advantages. This realization led to the emergence of fighters as a distinct category of aircraft. In the early days of the war, pilots and observers blazed away at enemy aircraft with pistols, rifles, and even shotguns, but to little effect. Machine guns were the obvious solution. In 1913 the Vickers company in Britain had exhibited a two-seat biplane of pusher configuration (i.e., with the propeller behind the engine) that was armed with a machine gun fired by an observer who sat ahead of the pilot in a tublike crew compartment. A development of this machine, the Vickers F.B.5 Gunbus, entered service in early 1915 as the first production aircraft designed from the outset with air-to-air armament. The French armed similarly configured Voisin pushers with machine guns (one had shot down a German aircraft as early as Oct. 5, 1914), but, burdened with the extra weight of observer and gun, such aircraft were slow and unmaneuverable, and their successes were mostly the result of accidental encounters. Light, single-seat aircraft of tractor configuration (i.e., with the propeller at the nose) had much better performance, but efforts to arm them with machine guns firing at an angle to avoid hitting the propeller produced little success.

The solution to the problem emerged in the spring of 1915 in the form of an interrupter gear, or gun-synchronizing device, designed by the French engineer Raymond Saulnier. This regulated a machine gun's fire so as to enable the bullets to pass between the blades of the spinning propeller. The interrupter itself was not new: a German patent had been taken out on such a device by the Swiss engineer Franz Schneider before the war. The real breakthrough was made by Roland Garros, a famous sporting pilot before the war and a friend of Saulnier, who perceived that a machine gun fitted with such a device and mounted rigidly atop the fuselage could be aimed accurately simply by pointing the airplane in the desired direction. Though the French machine gun had a tendency to "hang fire," so that steel deflector plates had to be fitted onto the rear of the propeller blades to prevent their being shot off, Saulnier quickly perfected his device and fitted it to Garros's Morane L monoplane. With this machine, Garros shot down three German aircraft on April 1, 13, and 18. Then, on April 19, Garros himself force-landed with a ruptured fuel line and was taken prisoner. His efforts to burn his aircraft failed, and the secrets of Saulnier's interrupter gear were laid bare. The Germans reacted quickly, putting the designer Anthony Fokker to work on a similar device. With Saulnier's gear as his inspiration (and perhaps drawing on earlier German work), Fokker swiftly came up with an efficient interrupter gear, which he fitted onto a monoplane of his own design--ironically, a copy of a French Morane. The result was the Fokker Eindecker ("monoplane"), which entered service in July 1915 and reigned supreme in the air over the Western Front until the following October--a period known among Allied aviators as the "Fokker Scourge."

The Eindecker's mastery was ended by new versions of the French Nieuport with a machine gun mounted above the top wing, allowing it to fire clear of the propeller arc, and by British D.H.2 and F.E.2b pushers with nose-mounted guns. Though a superb flying machine, the Nieuport was limited by its light armament, while the two British machines had brought the aerodynamically inefficient pusher configuration to its limit and were soon outclassed. Thereafter, the pace of fighter development began to be set by improvements in engine design--a phenomenon that was to persist well into the jet age.

Most Allied fighters at that time were powered by rotary radial engines (i.e., with the cylinders, arranged radially about the crankcase like the spokes of a wheel, rotating around a stationary crankshaft). These engines were relatively powerful in relation to their weight, but their large frontal areas produced a great deal of drag, and the gyroscopic forces induced by their whirling mass posed serious aircraft control problems. In mid-1916 Germany took the lead in fighter design on the basis of its superb Daimler and Benz water-cooled, in-line engines, such as those which powered the streamlined Albatros D.I, D.II, and D.III series of fighters. These were faster than their Allied opponents and, most important, could carry two machine guns without sacrificing performance. The Albatros D.I pioneered a fighter configuration that was to prevail into the 1930s: a compact, single-seat, externally braced tractor biplane armed with two synchronized machine guns mounted ahead of the pilot on the upper fuselage decking and aimed with a simple ring-and-bead sight. Albatros fighters gave British airmen a terrible drubbing above the Arras battlefield during the "Bloody April" of 1917, but a new generation of French and British fighters with more powerful engines soon tilted the balance toward the Allies. Prominent among these were the French Spad fighters and the British S.E.5, both powered by the Spanish-designed and French-built Hispano-Suiza watercooled V-8, as well as the British Sopwith Camel and new versions of the French Nieuport, powered by improved rotary radial engines.

Though Germany fell decisively behind France and Britain in aircraft production in 1917, and thus lost the war in the air, perhaps the definitive single-seat fighter of World War I was the Fokker D.VII of 1918. Typically powered by a 160-horsepower Mercedes engine, the D.VII was a fabric-covered biplane that differed from others in having a sturdy fuselage structure of welded steel tubing. Armed with two machine guns, it had a top speed of 117 miles per hour. Even more powerful engines made two-seat fighters possible; the best of these was the British Bristol F.2b, powered by the 220-horsepower, water-cooled Rolls-Royce Falcon, a V-12 engine that gave the Bristol a top speed of almost 120 miles per hour. The F.2b was armed with a synchronized machine gun for the pilot and two flexible machine guns for the observer.

3.10.2.4 Ground attack.

The Allies fielded specialized aircraft for ground attack only at the very end of the war. Notable among these was the Sopwith Salamander, a development of the Sopwith Camel with an armoured cockpit and two machine guns firing downward through the floor at a fixed angle to rake enemy trenches while flying low over them. The Germans produced a number of specialized two-seat aircraft for this purpose--notably the Halberstadt CL.III of 1917, which was armed with a forward-firing synchronized machine gun as well as a flexible gun and racks of grenades for the observer. At the Battle of Cambrai in November and December 1917, the Germans sent large formations of such aircraft over the British trenches and into the rear areas with devastating effect. By the end of the war, they were using numbers of armoured, all-metal Junkers J.1 ground-attack aircraft, one of the most advanced machines to see combat during the war.

3.10.2.5 Ground attack.

The Allies fielded specialized aircraft for ground attack only at the very end of the war. Notable among these was the Sopwith Salamander, a development of the Sopwith Camel with an armoured cockpit and two machine guns firing downward through the floor at a fixed angle to rake enemy trenches while flying low over them. The Germans produced a number of specialized two-seat aircraft for this purpose--notably the Halberstadt CL.III of 1917, which was armed with a forward-firing synchronized machine gun as well as a flexible gun and racks of grenades for the observer. At the Battle of Cambrai in November and December 1917, the Germans sent large formations of such aircraft over the British trenches and into the rear areas with devastating effect. By the end of the war, they were using numbers of armoured, all-metal Junkers J.1 ground-attack aircraft, one of the most advanced machines to see combat during the war.

3.10.2.6 Naval aviation.

Equally significant progress was made in naval flying in World War I. Three distinct categories of combat aircraft emerged: long-range over-water reconnaissance and antisubmarine aircraft operating from shore bases, shorter-range floatplane reconnaissance and fighter aircraft, and ship-borne aircraft. Long-range flying boats (so called because their fuselages were shaped like the hull of a boat) were used extensively by the British. These pioneered the technique of searching for submarines with methodical, mathematically developed search patterns. The German navy made extensive use of reconnaissance and fighter floatplanes from Belgian coastal bases to counter Allied air patrols and coastal naval operations. Some of these, notably Hansa-Brandenburg machines designed by Ernst Heinkel, rivaled their land-based equivalents in performance. (see also naval aircraft)

The most efficient of the long-range coastal-based airplanes were large, twin-engined flying boats designed by Glenn Curtiss and others. Despite their bulk, these aircraft were sufficiently fast and maneuverable to engage enemy zeppelins and aircraft in combat. Curtiss' flying boats were the only aircraft of U.S. design to see frontline combat service in World War I.

Carrier-based air power also advanced rapidly. In early 1916 the first landplanes (British Sopwith Pups) were flown off the 200-foot decks of primitive carriers that had been converted from merchant ships, and on Aug. 2, 1917, a pilot landed a Pup on the takeoff deck of HMS Furious while the ship was under way. The concept of the true aircraft carrier had been born.

Britain went on to develop more formidable naval aircraft, and in October 1918 a squadron of Sopwith Cuckoos, each able to carry an 18-inch torpedo, was embarked on HMS Argus. The war ended before the squadron could go into action; but the RNAS had already used torpedoes dropped from Short seaplanes to sink enemy ships in the Mediterranean, and the Cuckoo, with its modest top speed of 103 miles per hour and endurance of four hours, heralded the eventual demise of the battleship in the face of air-power dominance at sea. (see also torpedo plane)

3.10.2.7 Air transport and training.

Military air transport showed little development in 1914-18. Aircraft were used on occasion to drop supplies to cut-off or besieged forces, but the methods were primitive in the extreme: bags of food, medical supplies, or munitions were dropped from bomb racks or simply heaved over the side. (see also aviation)

Conversely, training made enormous strides during the war. At the RFC School of Special Flying at Gosport, Eng., Major Robert Smith-Barry introduced a curriculum based on a balanced combination of academic classroom training and dual flight instruction. Philosophically, Smith-Barry's system was based not on avoiding potentially dangerous maneuvers (as had been the case theretofore) but on exposing the student to them in a controlled manner so that he could learn to recover from them, thereby gaining confidence and skill. Technologically, it was based on the Avro 504J, a specialized training aircraft with dual controls, good handling characteristics, adequate power, and in-flight communication between instructor and student by means of an acoustic system of soft rubber tubing--the so-called Gosport tube. For the first time, military pilots flew into action as masters of their airplanes. The Gosport system of training was eventually adopted at training schools throughout the world, remaining the dominant method of civil and military flight instruction into the jet age.

3.10.3 INTERWAR DEVELOPMENTS

In the two decades between the end of World War I and the start of World War II, military aviation underwent a complete transformation. The typical combat aircraft of 1918 was a fabric-covered, externally braced biplane with fixed landing gear and open cockpits. Few aero engines developed as much as 250 horsepower, and top speeds of 120 miles per hour were exceptional. By 1939, the first-line combat aircraft of the major powers were all-metal monoplanes with retractable landing gear. Powered by engines that developed 1,000 horsepower or more and that were supercharged to permit flight at altitudes above 30,000 feet, fighters were capable of exceeding 350 miles per hour, and some bombers flew faster than 250 miles per hour. Gyroscopically driven flight instruments and electrical cockpit lighting permitted flying at night and in adverse weather. Crews were seated in enclosed cockpits, were provided with oxygen for breathing at high altitudes, and could converse with other aircraft and ground stations by voice radio. Parachutes, worn by a few German fighter pilots in the last days of World War I, were standard equipment.

Most of these changes occurred after 1930. The end of World War I left the victorious Allies with huge inventories of military aircraft, and this combined with economic strictures and a lack of threat to retard the development of military aviation in the 1920s. Provisions of the Treaty of Versailles prohibiting developments in military aviation had the same effect in Germany. Nevertheless, advances in key technologies, notably high-performance aero engines, continued. The U.S. government, for instance, sponsored a systematic program of aerodynamic research under the aegis of the National Advisory Committee for Aeronautics (NACA), which was to yield enormous dividends in aircraft performance through drag-reduction, engine-cooling, and airfoil technologies. Still, the most significant technical advance in the 1920s was the abandonment of wooden structures in favour of metal frames (still fabric-covered) to provide the strength needed to cope with increasingly powerful engines and to resist harsh climates around the world.

3.10.3.1 Civilian design improvements.

When more drastic changes came, they emerged not from military requirements but from civilian air racing, particularly the international seaplane contests for the coveted Schneider Trophy. Until the appearance of variable-pitch propellers in the 1930s, the speed of landplanes was limited by the lengths of existing runways, since the flat pitch of high-speed propellers produced poor takeoff acceleration. Seaplanes, with an unlimited takeoff run, were not so constrained, and the Schneider races, contested by national teams with government backing, were particularly influential in pushing speeds upward. During the 1920s the Curtiss company built a remarkable series of high-speed racing biplanes for the U.S. Army Air Corps and Navy. These were powered by the innovative D-12, a 12-cylinder, liquid-cooled engine, also of Curtiss design, that set international standards for speed and streamlining. One of the Curtiss planes, an R3C-2 piloted by Lieutenant James Doolittle, won the 1925 Schneider race with a speed of 232.5 miles per hour--in sharp contrast to the winning speed of 145.62 miles per hour in 1922, before the Curtiss machines took part in the event. The influence of the Curtiss engine extended to Europe when British manufacturer C.R. Fairey, impressed with the streamlining made possible by the D-12, acquired license rights to build the engine and designed a two-seat light bomber around it. The Fairey Fox, which entered service in 1926, advanced the speed of Royal Air Force (RAF) bombers by 50 miles per hour and was faster than contemporary fighters. Nor were British engine manufacturers idle; when the U.S. Army and Navy standardized on air-cooled radial engines in the 1920s, Curtiss ceased developing liquid-cooled engines, but British engine designers, partly inspired by the D-12, embarked on a path that was to produce the superlative Rolls-Royce Merlin.

The year that Doolittle won the Schneider Trophy, an even more revolutionary design appeared--the S.4 seaplane designed by R.J. Mitchell of the British Supermarine Company. A wooden monoplane with unbraced wings, the S.4 set new standards for streamlining, but it crashed from wing flutter before it could demonstrate its potential. Nevertheless, it was the progenitor of a series of monoplanes that won the trophy three times, giving Britain permanent possession in 1931. The last of these, the S.6B, powered by a liquid-cooled Rolls-Royce racing engine with in-line cylinders, later raised the world speed record to more than 400 miles per hour. The S.6B's tapered fuselage and broad, thin, elliptical wings were clearly evident in Mitchell's later and most famous design, the Spitfire.

In the United States the Thompson Trophy, awarded to the winner of unlimited-power closed-circuit competitions at the National Air Races, was won in 1929 for the first time by a monoplane, the Travel Air "R" designed by J. Walter Beech. Powered by the Wright Cyclone, a 400-horsepower radial engine with a streamlined NACA cowling that contributed 40 miles to its maximum speed of 235 miles per hour, the "R" handily defeated the far more powerful Curtiss biplanes flown by the army and navy. Embarrassed, the military withdrew from racing--and the army soon ordered its first monoplane fighter, the Boeing P-26. In 1935 the industrialist Howard Hughes set a world landplane speed record of 352 miles per hour in a racer designed to his own specifications and powered by a 1,000-horsepower, twin-row radial engine built by Pratt & Whitney. The Hughes H-1 was a low-wing monoplane built with unbraced wings with a "stressed-skin" metal covering that bore stress loads and thereby permitted a reduction in weight of the internal structure. These features, along with a flush-riveted, butt-joined aluminum fuselage, an enclosed cockpit, and power-driven, retractable landing gear folding flush into the wing, anticipated the configuration, appearance, and performance of the fighters of World War II.

3.10.3.2 Fighters.

By the 1930s the advantages of monoplanes with unbraced wings and retractable landing gear were evident, and fighters of this description began to appear. The first of these to see operational service was the Soviet I-16, designed by Nikolay Polikarpov. The I-16 first flew in 1933 and enjoyed considerable success against German and Italian biplanes in the Spanish Civil War of 1936-39. Powered by a radial engine derived from the Wright Cyclone, it had manually retracted landing gear and an open cockpit; its armament of four 7.62-millimetre machine guns, two in the wings and two in the engine cowling, was heavy for the time.

As the I-16 entered combat in Spain, two important British fighters were under development: the Supermarine Spitfire, a cleanly elegant fighter of stressed-skin aluminum construction, and the Hawker Hurricane, a more traditional design with a structural frame of welded steel tubes and a fabric covering over the rear fuselage. Both were powered by a Rolls-Royce Merlin engine of some 1,200 horsepower, and both carried an unprecedented armament of no fewer than eight .303-inch Browning machine guns, mounted in the wings outboard of the propeller arc so that no interrupter gear was needed. Meanwhile, in Germany the nascent Luftwaffe (Air Force) was taking delivery of the first versions of the Bf 109, designed by Willy Messerschmitt for the Bayerische Flugzeugwerke ("Bavarian Aircraft Factory"). Like the Spitfire, the Bf 109 was a low-wing monoplane of all-metal, stressed-skin construction. Early versions, fitted with fixed-pitch propellers, fought on a par with the I-16 in Spain, but later versions, powered by a Daimler-Benz engine that was equivalent to the Merlin and fitted with variable-pitch propellers for optimal performance at low and high altitudes, totally outclassed the Russian fighter.

3.10.3.3 Bombers.

Bombers evolved in parallel with fighters, changing to high-strength metal construction in the late 1920s and to monoplane design, which brought higher speeds, in the early 1930s. In 1931 the Boeing Aircraft Company produced the B-9 bomber. Anticipating all-metal fighters, the B-9 was the first operational combat aircraft with all-metal cantilever monoplane design, semiretractable undercarriage, and variable-pitch propellers. Two 600-horsepower engines gave it a speed of 188 miles per hour, representing a 50-percent improvement over the biplane bombers then in service, without any reduction in bombload. Within months of its first flight, the B-9 was overshadowed completely by the Martin B-10 of 1932, which brought the biggest single advance in bomber design since the Handley Page night bomber of World War I. To the innovations of the B-9 it added enclosed cockpits and an internal bay for its 2,260-pound bombload. Maximum speed went up to 213 miles per hour, making the B-10 faster than the fighters of its day. Following this success, Boeing built in 1935 a four-engined craft known as the Model 299, which became the prototype of the B-17 Flying Fortress. This famous plane was based on the concept that a bomber could penetrate to any target in daylight as long as it had sufficient defensive armament to battle past fighter opposition. Gun turrets for defensive machine guns had already been pioneered by Machines Motrices in France, and a license-built version of their turret had appeared on the British Boulton Paul Overstrand bomber in 1934. Meanwhile, the U.S. Army Air Corps claimed that its highly secret Norden bombsight provided such accuracy that "a bomb could be placed in a pickle barrel from 20,000 feet."

An important type of bomber to emerge in the interwar period was the dive-bomber, designed to release its bombs at a low point of a steep dive. Accuracy was maintained by the use of airbrakes, which were flaps that could be extended outward to slow the dive by increasing the aircraft's drag. The dive-bomber as a distinct type of aircraft was a product of tests undertaken during the 1920s by the U.S. Navy. These demonstrated the advantages of bombing the lightly armoured upper decks of warships and resulted in the appearance of the first real dive-bomber, the Curtiss F8C Helldiver, in 1929. Impressed by a Helldiver demonstration, the Luftwaffe, whose doctrine stressed the direct support of ground forces, requested a more advanced aircraft with similar capabilities. The result was the Ju 87 "Stuka" (for Sturzkampfflieger, or "dive-bomber"), which gained a fearsome reputation for destructiveness during the Spanish Civil War.

3.10.3.4 Carrier aircraft.

By the 1930s, ship-based aircraft were fitted under the tail with arrester hooks that engaged cables strung across the landing deck in order to bring them to a halt after landing. Folding wings then enabled them to be taken by elevator to below-deck hangars. Japanese and U.S. aircraft carriers had mixed complements of single-seat fighters, dive-bombers, and torpedo planes; the Royal Navy pursued a less successful course, developing two-seat reconnaissance fighters, such as the Fairey Fulmar, which were outperformed by their land-based equivalents.

3.10.4 WORLD WAR II

3.10.4.1 Fighters.

3.10.4.1.1 Day fighters.

Air superiority was crucial to the outcome of most of the decisive campaigns of World War II, and here the performance of single-seat fighters was generally the critical factor. First-class fighters required extremely powerful aero engines suitable for compact, low-drag installation, and in this respect Britain, Germany, and the United States were in a class by themselves. The only significant exception was the Japanese Mitsubishi A6M carrier fighter, known as the Zero. Designed by Horikoshi Jiro, the Zero was so remarkably strong and light that it achieved first-class performance with a second-class engine--though at the cost of being vulnerable to battle damage.

The outstanding fighters of the early war years (1939-41) were the Spitfire, Bf 109 (known to the wartime Allies as the Me 109), Zero, Hurricane, and Grumman F4F Wildcat (this last a U.S. Navy fighter powered by a turbosupercharged, twin-row radial engine by Pratt & Whitney). The Lockheed P-38 Lightning (see photograph), a novel twin-boom interceptor designed before the war by Clarence ("Kelly") Johnson, had exceptional performance, but until 1943 it was available only in small numbers. The main U.S. Army Air Force fighters of the early war, the Curtiss P-40 Warhawk and the Bell P-39 Airacobra, were badly outclassed by the Bf 109 and Zero as a result of production decisions that deprived their high-performance Allison engines of scarce turbosuperchargers, assigning them instead to bombers. The best Soviet fighters were similarly outclassed: the MiG-3, designed by a bureau headed by Artem Mikoyan and Mikhail Gurevich, was fast, but it had marginal handling characteristics at low altitudes, and the performance of Semyon Lavochkin's LaGG-3 was ruined by a disastrously heavy airframe.

The Spitfire and Hurricane were determined opponents of the Bf 109 during the Battle of Britain, the first battle fought entirely in the air. The German fighter was armed with two machine guns in the cowling and two wing-mounted cannon firing 20-millimetre exploding shells. Aerial cannon, perfected by the Germans during the war, was intended to ensure the greatest possible destruction against metal-skinned aircraft in the short periods during which a target could be kept in the gunsights at rapidly increasing speeds. It was superior in fighter-to-fighter combat, while the massed batteries of .303-inch machine guns in the British fighters were highly effective in destroying bombers. Aiming was accomplished by gyroscopic lead-computing gunsights that projected the aim point onto a transparent screen in front of the pilot.

More powerful and heavily armed versions of the Spitfire and Bf 109 were tactically viable through the end of the war, but they were hampered by a short radius of action (the farthest distance to which they could fly, engage in combat, and return to base). In 1942-43, fighters began to enter service fitted with newer and more powerful engines and designed on the basis of the most recent aerodynamic data. Notable among these were the German Focke-Wulf Fw 190, designed by Kurt Tank, and the U.S. Republic P-47 Thunderbolt, Grumman F6F Hellcat, and North American P-51 Mustang. All were heavily armed, the Fw 190 with as many as two 7.6-millimetre machine guns and four 20-millimetre cannon, the P-47 eight .50-inch machine guns, and the F6F and P-51 six .50-inch machine guns. The Fw 190, P-47, and F6F had distinctively bulky fuselages widened to accommodate their twin-row radial engines, while the slimmer P-51, designed in 1940 by J.H. ("Dutch") Kindleberger under a British contract, was fitted with in-line engines and incorporated the latest drag-reduction and airfoil data provided by NACA. Powered by the Rolls-Royce Merlin, the P-51 became the outstanding high-altitude escort fighter of the war. It was at least competitive with contemporary versions of the Spitfire, Bf 109, and Fw 190 in speed, rate of climb, and maneuverability, but it had a more spacious fuselage, a more efficient wing, and, fitted with droppable fuel tanks, a far greater radius of action of more than 1,000 miles. During 1943 the Soviet Red Air Force also gained technical parity with the Luftwaffe with its radial-engined Lavochkin La-5 and La-7 and the in-line-powered Yakovlev Yak-3 and Yak-9.

By war's end, piston-engined fighter technology reached its peak in later versions of the Fw 190, powered by in-line Jumo engines by Junkers, and in the Hawker Tempest, powered by the massive 2,200-horsepower, 24-cylinder, in-line Napier Sabre. Armed with four 20-millimetre cannon and able to attain speeds in excess of 435 miles per hour, the Tempest was the fastest piston-engined fighter ever to see service.

3.10.4.1.2 Night fighters.

During the Battle of Britain, the RAF converted twin-engined bombers such as the Bristol Blenheim into night fighters by installing offensive ordnance and radar, but these had little success, since they were no faster than their prey. On the other hand, Messerschmitt's Me 110, a disastrous failure as a twin-engined, two-seat day fighter, became highly successful at night fighting, as did similarly modified Ju 88 bombers. The RAF later used radar-equipped versions of the de Havilland Mosquito to protect its bombers during the battle for the night skies over Germany in 1943-45.

3.10.4.2 Ground attack.

The most effective attack aircraft of the war was the Soviet Ilyushin Il-2 Stormovik. Heavily armoured for protection against ground fire and defended by a gunner in the rear of the two-seat cabin, the Il-2 could fly at up to 280 miles per hour at treetop level and was able to attack ground targets with cannons, bombs, and rockets. It was the first close-support type to employ rockets in vast quantities and had a great influence on the adoption of such weapons by other Allied forces. Another important ground-attack aircraft was Britain's Hawker Typhoon, originally intended to be a high-altitude fighter but limited to low altitudes by its thick wing. Armed with rockets and 20-millimetre cannon, it specialized in attacking trains, tanks, and other moving ground targets.

3.10.4.3 Bombers.

The Stuka dive-bomber was used to great effect during the invasions of Poland, France, and the Low Countries in 1939-40, but its slow speed rendered it vulnerable to fighter attack. The Germans' principal bombers of the Battle of Britain were the twin-engined Heinkel He 111, Dornier Do 17, and Ju 88. The Ju 88 was fast, with a top speed of 280 miles per hour, but it carried a modest bombload; the other German bombers had mediocre performance and were lightly armed by British or American standards. The later Do 217 had a range of 1,500 miles and could carry a bombload of 8,800 pounds, but it was built only in small numbers. The Germans never built a successful four-engined bomber. (see also bombing)

Combat experience showed that the heavily armed British and U.S. bombers were more vulnerable to fighter attack than expected. This was dramatically revealed on Dec. 18, 1939, when a formation of Vickers Wellingtons--the most battle-worthy bombers of the day with four-gun Boulton Paul tail turrets--was decimated over the Heligoland Bight by cannon-armed German fighters. In time this led to the adoption of self-sealing fuel tanks, armour protection for crews, and even heavier defensive armament, but the British responded immediately by abandoning daylight bombing except under special circumstances. Bombing at night reduced vulnerability to fighters, but finding and hitting targets proved difficult: nothing smaller than a city could be effectively attacked, and, as operational analysis revealed in 1941-42, ordinary crews had trouble doing even that. The problem was solved partly by using specially trained "Pathfinder" crews to mark targets with flares and partly by electronic navigation aids. During the Battle of Britain, the Germans used electronic beams to guide bombers to their targets at night, and the British later developed such on-board radars as the H₂S blind bombing system, which could produce maplike pictures of terrain beneath the aircraft through clouds or in darkness. From 1943, powerful four-engined bombers such as the Handley Page Halifax and Avro Lancaster, carrying H₂S radar and heavy armament, kept RAF bomber losses within barely acceptable limits. (see also Wellington bomber, H2S)

An independent British development was the de Havilland Mosquito. Constructed entirely of wood, powered by two Rolls-Royce Merlin engines, and carrying a crew of two and no defensive armament, this extraordinarily fast aircraft remained effectively immune to interception until the appearance of jet fighters, and it could reach Berlin with a 4,000-pound bomb. It was perhaps the most successful multimission aircraft ever made, serving with distinction as a low-level day bomber, radar-equipped night fighter, and long-range photoreconnaissance aircraft.

The U.S. Army Air Force armed later versions of its B-17 Flying Fortresses and Consolidated-Vultee B-24 Liberators with 12 or more .50-inch machine guns, eight of them in twin-gun, power-driven turrets in nose, tail, ventral, and belly positions. Still, losses were high, reaching unacceptable numbers in raids against the Schweinfurt ball-bearing works on Aug. 17 and Oct. 14, 1943. Daylight bombing had to be curtailed until the arrival of P-38, P-47, and P-51 escort fighters equipped with drop tanks to provide the necessary range. For high-altitude attacks from 25,000 feet, the B-17 could carry 4,000 pounds of bombs at 215 miles per hour with a radius of action of some 800 miles. The B-24 carried more bombs and was slightly faster, but it could not fly as high and was more vulnerable to enemy fire. British heavy bombers carried larger bombloads--the Lancaster could carry 7,000 pounds with a radius of action of nearly 1,000 miles or a bombload of 14,000 pounds over a radius of 500 miles--but only at medium altitudes of less than 20,000 feet. The heaviest bomber of World War II was the Boeing B-29 Superfortress, which entered service in 1944 with a fully pressurized crew compartment (previously used only on experimental aircraft) and as many as 12 .50-inch machine guns mounted in pairs in remotely-controlled turrets. Although these features were intended to optimize the B-29 for very high-altitude missions at 35,000 feet, it was most effectively used when, stripped of almost all its heavy defensive armament, it carried bombloads as heavy as 12,000 pounds in low altitude firebombing attacks against Tokyo and other Japanese cities from bases 2,000 miles away in the Mariana Islands. Specially modified B-29s dropped atomic bombs on Hiroshima and Nagasaki. (see also United States Air Force, The)

3.10.4.4 Naval aviation.

During World War II, carrier-based attack aircraft replaced the big guns of capital ships as the dominant offensive weapon of naval warfare. This was first demonstrated by the destruction of Italian battleships at Taranto by Fairey Swordfish torpedo biplanes on the night of Nov. 11-12, 1940; by the Japanese attack on Pearl Harbor on Dec. 7, 1941; and by the decisive Battle of Midway (June 3-6, 1942), in which surface vessels never exchanged gunfire while U.S. aircraft destroyed four Japanese aircraft carriers for the loss of only one of their own. In addition to such fighters as the F6F, Zero, and modified Spitfires and Hurricanes, notable carrier aircraft of the war included dive-bombers such as the U.S. Douglas SBD Dauntless and Japanese Aichi 99 as well as torpedo planes such as the Grumman TBF Avenger and Nakajima B5N.

Land-based torpedo planes were also effective, as shown in attacks on the British battleships Repulse and Prince of Wales by twin-engine Japanese Mitsubishi G3M bombers off Malaya on Dec. 10, 1941.

Kamikaze attacks, a Japanese suicide tactic first used in the Battle of Leyte Gulf on Oct. 25, 1944, were very destructive as long as the supply of skilled volunteer pilots held out. First conducted with bomb-armed Zero fighters, they later expanded to encompass bombers and such special craft as a piloted, rocket-propelled winged bomb called the Ohka ("Cherry Blossom"). By the end of the war, however, there were no more skilled kamikaze volunteers, and the tactic became no more effective than traditional dive bombing.

3.10.4.5 Reconnaissance.

For military staffs contemplating offensive operations, aerial photography became the most important source of detailed information on enemy dispositions. British reconnaissance aircraft were especially capable. Modified versions of the Spitfire and Mosquito, stripped of armament and fitted with extra fuel tanks, proved essentially immune to interception at high altitudes. Stripped-down versions of the P-38 and P-51, called the F-4 and F-5, were also effective photoreconnaissance platforms, the latter excelling at high-resolution coverage from low altitudes. (see also aerial reconnaissance)

3.10.4.6 Training.

Japan and Germany entered World War II with exceptionally well-trained aviators, but their provisions for training replacements were inadequate. The British Commonwealth and the United States gained a vital advantage over the Axis by establishing large, well-organized air-crew training programs. Outstanding training aircraft included the British de Havilland Tiger Moth, the U.S. Stearman PT-19, and the German Bücker Bü 133 Jungmeister--all biplanes. Only the United States built specialized single-engined trainers with such features characteristic of operational craft as retractable landing gear and variable-pitch propellers. Notable among these was the North American AT-6.

3.10.4.7 Air transport.

Major advances in air transport were made during the war. Mass drops of parachute troops had been pioneered by the Soviet Union in the 1930s, but the Luftwaffe first used the technique operationally, notably during the invasion of Crete, in which 15,000 airborne and parachute troops were landed onto that island by 700 transport aircraft and 80 gliders. The troop-carrying glider was one of the developments of World War II that had no continuing place in postwar air forces, but the transport airplane was only at the beginning of its useful life. The Germans built transports such as the Ju 52 only in small quantities, but the twin-engined Douglas C-47, which had revolutionized American commercial aviation in the mid-1930s as the DC-3, was produced in huge numbers and was the backbone of tactical air transport in every Allied theatre of the war. One of the few transports with a large side door suitable for dropping paratroopers, the C-47 was also the mainstay of British and American airborne operations. Douglas also manufactured the four-engined C-54, which entered service in 1943-44 as the first land-based transport with intercontinental flight capabilities. The C-54 was particularly important in the vast distances of the Pacific-Asian theatre of operations.

3.10.4.8 Helicopters.

In the years before World War II, both the U.S. Army and the RAF had experimented with autogiros; these were craft that employed a propeller for forward motion and a freely rotating, unmotorized rotor for lift. In the event, autogiros proved too expensive and mechanically complex and were supplanted by conventional light aircraft. Meanwhile, during the late 1930s Igor Sikorsky in the United States and Anton Flettner and Heinrich Focke in Germany had perfected helicopter designs with serious military potential. The Sikorsky R-4, powered by a single lifting rotor and an antitorque tail rotor, was used for local rescue duties at U.S. air bases in the Pacific and was also used in several combat rescues in Burma. The German navy used a handful of Flettner Fl 282s, powered by two noncoaxial, contrarotating lifting rotors, for ship-based artillery spotting and visual reconnaissance.

3.10.5 THE JET AGE

Beginning in the 1920s, steady advances in aircraft performance had been produced by improved structures and drag-reduction technologies and by more powerful, supercharged engines, but by the early 1930s it had become apparent to a handful of farsighted engineers that speeds would soon be possible which would exceed the capabilities of reciprocating engines and propellers. The reasons for this were not at first widely appreciated. At velocities approaching Mach 1, or the speed of sound (about 745 miles per hour at sea level and about 660 miles per hour at 36,000 feet), aerodynamic drag increases sharply. Moreover, in the transonic range (between about Mach 0.8 and Mach 1.2), air flowing over aerodynamic surfaces stops behaving like an incompressible fluid and forms shock waves; these in turn create sharp local discontinuities in airflow and pressure, creating problems not only of drag but of control as well. Because propeller blades, describing a spiraling path, move through the air at higher local velocities than the rest of the aircraft, they enter this turbulent transonic regime first. For this reason, there is an inflexible upper limit on the speeds that can be attained by propeller-driven aircraft. Such complex interactions in the transonic regime--and not the predictable shock-wave effects of supersonic flight, which ballisticians had understood since the late 19th century--presented special problems that were not solved until the 1950s. In the meantime, a few pioneers attacked the problem directly by conceiving a novel power plant, the turbojet.

While still a cadet at the Royal Air Force College, Cranwell, in 1928, Frank Whittle advanced the idea of replacing the piston engine and propeller with a gas turbine, and in the following year he conceived the turbojet, which linked a compressor, combustion chamber, and turbine in the same duct. In ignorance of Whittle's work, three German engineers independently arrived at the same concept: Hans von Ohain in 1933; Herbert Wagner, chief structural engineer for Junkers, in 1934; and government aerodynamicist Helmut Schelp in 1937. Whittle had a running bench model by the spring of 1937, but backing from industrialist Ernst Heinkel gave von Ohain the lead. The He 178, the first jet-powered aircraft, flew on Aug. 27, 1939, nearly two years before its British equivalent, the Gloster E.28/39, on May 15, 1941. Through an involved chain of events in which Schelp's intervention was pivotal, Wagner's efforts led to the Junkers Jumo 004 engine. This became the most widely produced jet engine of World War II and the first operational axial-flow turbojet, one in which the air flows straight through the engine. By contrast, the Whittle and Heinkel jets used centrifugal flow, in which the air is thrown radially outward during compression. Centrifugal flow offers advantages of lightness, compactness, and efficiency--but at the cost of greater frontal area, which increases drag, and lower compression ratios, which limit maximum power. Many early jet fighters were powered by centrifugal-flow turbojets, but, as speeds increased, axial flow became dominant.

3.10.5.1 Early jet fighters.

3.10.5.1.1 Subsonic flight.

Though Whittle was first off the mark, the Germans advanced their programs with persistence and ingenuity. The Messerschmitt Me 262, powered by two Jumo engines and with wings swept back 18.5°, was capable of 525 miles per hour. Armed with four 30-millimetre cannon and unguided rockets, it was an effective bomber destroyer, but it entered service too late to have a major effect on the war. The Gloster Meteor entered service on July 27, 1944, about two months before the Me 262; though it was less capable than the German fighter, it was effective in intercepting V-1 "buzz bombs." Desperate to combat Allied bombers, the Germans also turned to rocket propulsion, fielding the tailless Me 163 Komet in the final months of the war. Powered by a hydrogen peroxide rocket designed by Helmuth Walter, the Komet had spectacular performance, but its short range and ineffective cannon armament made it an operational failure. In addition, the propellants were unstable and often exploded on landing. (see also Me 163)

Meanwhile, the U.S. aviation industry entered the jet race with the receipt by General Electric of a Whittle engine in 1941. The first U.S. jet, the Bell P-59A Airacomet, made its first flight the following year. It was slower than contemporary piston-engined fighters, but in 1943-44 a small team under Lockheed designer Kelly Johnson developed the P-80 Shooting Star. The P-80 and its British contemporary, the de Havilland Vampire, were the first successful fighters powered by a single turbojet.

The jets of World War II inaugurated the first generation of jet fighters, in which turbojet propulsion was applied to existing airframe technology and aerodynamics. (Indeed, some early postwar jets--notably, the Soviets' Yakovlev Yak-15 and Yak-23 and the Swedish Saab 21R--were simply re-engined propeller-driven fighters.) These aircraft generally outperformed their piston-engined contemporaries by virtue of the greater thrust that their jets provided at high speeds, but they suffered from serious deficiencies in range and handling characteristics owing to the high fuel consumption and slow acceleration of early turbojets. More fundamentally, they were limited to subsonic speeds because the relatively thick airfoils of the day were prone to the compressibility problems of transonic flight--especially at high altitudes, where the higher speeds required to produce lift in thin atmosphere brought aircraft more quickly to transonic speed. For this reason, first-generation jets performed best at low altitudes.

Other first-generation fighters included the U.S. McDonnell FH Phantom and the British Hawker Sea Hawk (the first jet carrier fighters), the McDonnell F2H Banshee, and the French Dassault Ouragan. These single-seat day fighters were in service by 1950, while first-generation all-weather fighters, burdened with radar and a second crew member, entered service through the late 1950s.

3.10.5.1.2 Transonic flight.

As the first generation of jet fighters entered service, many aerodynamicists and engineers believed supersonic flight a practical impossibility, owing to transonic drag rise or compressibility, which threatened to tear an aircraft apart. Nevertheless, on Oct. 14, 1947, U.S. Air Force Captain Charles Yeager, flying a rocket-powered Bell X-1 launched from the bomb bay of a B-29, became the first human to exceed the speed of sound. Designed exclusively for research, the X-1 had thin, unswept wings and a fuselage modeled after a .50-inch bullet. Yeager's flight marked the dawn of the supersonic era, but it was only part of a broad wave of testing and experimentation that had begun during World War II. Germany had experimented then with swept-back and delta-shaped wings, which delayed transonic drag rise, and, after extensive testing, these configurations were widely adopted in the postwar years. At the same time, the development of slats, slotted flaps, and other sophisticated high-lift devices for landing and takeoff enabled designers to use smaller wings, which in turn allowed them to achieve higher speeds. Turbojets became more powerful, and, in the late 1950s, afterburning, or reheat, was introduced; this permitted large temporary thrust increases by the spraying of fuel into hot exhaust gases in the tailpipe--in effect turning the turbojet into a ramjet.

As these developments took hold, a second generation of fighters appeared that were capable of operating in the transonic regime. These aircraft had thinner lifting and control surfaces than first-generation jets, and most had swept-back wings. Aerodynamic refinements and more powerful, quicker-accelerating engines gave them better flight characteristics, particularly at high altitudes, and some could exceed the Mach in a shallow dive. In addition, airborne radars became more compact and reliable, and radar-ranging gunsights began to replace the optically ranging sights used in World War II. Air-to-air missiles, using radar guidance and infrared homing, became smaller and more capable (see above Rockets and missile systems: Tactical guided missiles ). Outstanding fighters of this generation were the U.S. North American F-86 Sabre and its opponent in the Korean War (1950-53), the Soviet MiG-15. The F-86 introduced the all-flying tail (later a standard feature on high-performance jets), in which the entire horizontal stabilizer deflects as a unit to control pitch, yielding greater control and avoiding the compressibility problems associated with hinged surfaces. This and a radar-ranging gunsight helped the F-86 achieve a favourable kill ratio over the MiG-15, despite the Soviet fighter's greater speed, higher service ceiling, and heavier armament. Other jets of this generation were Britain's superlative Hawker Hunter, the MiG-17, and the diminutive, British-designed Folland Gnat. The latter two, introduced in the mid-1950s, later became successful low-altitude dogfighters--the Gnat against Pakistani F-86s in the Indo-Pakistani conflict of 1965 and the MiG-17 against U.S. aircraft in the Vietnam War (1965-73).

3.10.5.2 Modern jet fighters.

3.10.5.2.1 Supersonic flight.

A third generation of fighters, designed around more powerful, afterburning engines and capable of level supersonic fight, began to enter service in the mid-1950s. This generation included the first fighters intended from the outset to carry guided air-to-air missiles and the first supersonic all-weather fighters. Some were only marginally supersonic, notably the U.S. Convair F-102 Delta Dagger, an all-weather interceptor that was the first operational "pure" delta fighter without a separate horizontal stabilizer. Other aircraft included the Grumman F11F Tigercat, the first supersonic carrier-based fighter; the North American F-100 Super Sabre; the Dassault Mystère B-2; the Saab 35, with a unique double-delta configuration; and the MiG-19.

To this point, jet fighters had been designed primarily for air-to-air combat, while older aircraft and designs falling short of expectations were adapted to ground attack and reconnaissance. Since land-based surface attack was to be carried out by bombers, the first operational jets of fighter size and weight designed to attack surface targets were based on aircraft carriers. These paralleled the third generation of fighters, but they were not supersonic. One example was the British Blackburn Buccaneer, capable of exceptional range at low altitudes and high subsonic speeds. The Douglas A-4 Skyhawk, entering service in 1956, sacrificed speed for ordnance-delivery capability. One of the most structurally efficient aircraft ever built, it carried the burden of U.S. Navy attacks on ground targets in North Vietnam and was often used by Israeli pilots in the Middle Eastern conflicts. The Grumman A-6 Intruder, which entered service in the 1960s, was another subsonic carrier-based aircraft. The first genuine night/all-weather, low-altitude attack aircraft, it was highly successful over North Vietnam.

3.10.5.2.2 Mach 2.

A fourth generation of fighters began to appear in the 1960s, capable of maximum speeds ranging from about Mach 1.5 to 2.3. Top speeds varied with the intended mission, and increasing engine power, aerodynamic sophistication, and more compact and capable radars and avionics began to blur the differences between two-seat, all-weather fighters and single-seat air-superiority fighters and interceptors. By this time, military designers had become persuaded that air-to-air missiles had made dogfighting obsolete, so that many interceptors were built without guns. This generation included the first land-based jet fighters designed with surface attack as a secondary or primary mission--a development driven by the appearance of surface-to-air missiles such as the Soviet SA-2, which denied bombers medium- and high-altitude penetration.

Precursor to this generation was the Lockheed F-104 Starfighter, designed by a team under Kelly Johnson and first flown in 1954. Capable of speeds well above Mach 2, this interceptor was built with short and extremely thin wings to reduce the generation of shock waves. However, light armament, limited avionics, and poor maneuverability made it an ineffective air-to-air fighter, and only with the installation of up-to-date bombing and navigation systems in the 1960s did it become a useful low-level attacker. The truly outstanding fighters were the U.S. McDonnell F-4 Phantom II and the MiG-21. A large, twin-engined two-seater, the F-4 was originally a carrier-based interceptor armed only with air-to-air missiles, but it was so successful that the U.S. Air Force adopted it as its primary fighter. When combat in Vietnam showed that gun armament was still valuable for close-range dogfighting, later versions of the F-4 were fitted with an internally mounted, 20-millimetre rotary cannon. The MiG-21 was a small, delta-wing, single-seat aircraft designed as a specialized daylight interceptor, but it soon proved amenable to modification for a broad range of missions and became the most widely produced jet fighter ever. It was a formidable threat to U.S. airmen over North Vietnam and to Israeli pilots over the Sinai Peninsula and Golan Heights in 1973. Also outstanding was the Republic F-105 Thunderchief, one of the largest single-engined fighters ever built. Designed to carry a nuclear bomb internally as a low-altitude penetrator and therefore exceptionally fast at low altitudes, the F-105, with heavy loads of conventional bombs under the wings, carried out the brunt of U.S. Air Force attacks against North Vietnam. Also noteworthy in this generation were the British Electric Lightning, one of the first Mach-2 interceptors to enter service and one of the fastest at high altitudes; the Soviets' twin-engined, all-weather Yak-28 Firebar; the Convair F-106 Delta Dart, a single-seat air-defense interceptor with superior speed and maneuverability; the Dassault Mirage III, the first successful pure delta in the air-to-air role and an enormous export success; the Soviet Sukhoy Su-21 Flagon, a tailed-delta, single-seat, all-weather interceptor; and the Vought F-8 Crusader, an outstanding carrier-based dogfighter over Vietnam.

3.10.5.2.3 Multimission.

By the 1970s, steady improvements in engine performance, aerodynamics, avionics, and aircraft structures resulted in a trend toward multimission fighters. Also, as engine acceleration characteristics improved dramatically and radars, fire-control systems, and air-to-air missiles became more compact and capable, the performance of aircraft themselves became less important than the capabilities of their missiles and sensors. It was now clear that, even with supersonic aircraft, almost all aerial combat occurred at transonic and subsonic speeds. Thenceforth, speed and operating ceiling were traded off against sustained maneuvering energy, sensor capabilities, mixed ordnance of guns and missiles, range, takeoff and landing qualities, multimission capability, political goals, and--above all--cost. A dramatic manifestation of the complexity of this new design equation was the Hawker Harrier, the first vertical/short takeoff and landing (V/STOL) fighter. Transonic and short-ranged but able to dispense with runways, the Harrier became operational with the RAF in 1967 and over the following decades was fitted with avionics of growing capabilities. The Royal Navy's Sea Harrier version (see photograph) distinguished itself in the 1982 Falkland Islands War both against Argentine ground positions and in dogfights with A-4s and Mirage IIIs.

The new generation of fighters was characterized by Mach 2+ performance where necessary, multimission capability, and sophisticated all-weather avionics. Many aircraft of this generation employed variable-geometry wings, permitting the amount of sweep to be changed in flight to obtain optimal performance for a given speed. Important aircraft in this generation included, roughly in order of operational appearance, the following: the MiG-25 Foxbat, a large single-seat interceptor and reconnaissance aircraft with a service ceiling of 80,000 feet and a top speed on the order of Mach 2.8 but with limited maneuverability and low-altitude performance; the MiG-23 Flogger, a variable-wing interceptor able to acquire and engage with missiles below it in altitude; the MiG-27 Flogger, a ground-attack derivative of the MiG-23; the Saab 37 Viggen, designed for short takeoff with a main delta wing aft and small delta wings with flaps forward; the fixed-wing Sepecat Jaguar, developed by a French-British consortium in ground-attack and interceptor versions; the Grumman F-14 Tomcat, a highly maneuverable, twin-engined, two-seat, variable-geometry interceptor armed with long-range missiles for the defense of U.S. aircraft-carrier fleets; the Dassault-Breguet Mirage F1, designed for multimission capability and export potential; the McDonnell Douglas F-15 Eagle, a single-seat, twin-engined, fixed-geometry air-force fighter designed for maximum sustained maneuvering energy and the first possessor of a genuine "look-down/shoot-down" capability, which was the product of pulse-Doppler radars that could detect fast-moving targets against cluttered radar reflections from the ground; the Panavia Tornado, a compact, variable-geometry aircraft developed jointly by West Germany, Italy, and Great Britain in no fewer than four versions, ranging from two-seat, all-weather, low-altitude attack to single-seat air-superiority; the U.S. General Dynamics F-16 Fighting Falcon, a high-performance, single-seat multirole aircraft with impressive air-to-ground capability; the MiG-29 Fulcrum, a single-seat, twin-engined, fixed-geometry interceptor with a look-down/shoot-down capability; the MiG-31 Foxhound interceptor, apparently derived from the MiG-25 but with less speed and greater air-to-air capability; and the McDonnell Douglas F/A-18 Hornet, a single-seat, carrier-based aircraft designed for ground attack but also possessing excellent air-to-air capability.

3.10.5.3 Bombers.

3.10.5.3.1 High-altitude craft.

The Luftwaffe fielded the first operational jet bomber, the Arado Ar 234, in the waning months of World War II, but it had minimal impact. The jet bombers of the immediate postwar years enjoyed only indifferent success, mostly serving to test engineering and operational concepts and being produced in small numbers. By the mid-1950s, however, first the Americans and then the British and Soviets began to field highly capable jet bombers. The first of these to be produced in large numbers was the swept-wing, six-engined Boeing B-47 Stratojet, used by the U.S. Strategic Air Command as a long-range nuclear weapons carrier. Deployed in 1950, it was followed in 1955 by the eight-engined Boeing B-52 Stratofortress. This huge bomber, 153 feet long and with a wing span of 185 feet, remained the principal long-range nuclear weapons carrier of the United States for 30 years. During the Vietnam War it dropped conventional bombs on both tactical and strategic missions, and in the 1980s it received a new lease on life by being fitted with air-launched cruise missiles, which permitted it to threaten targets from beyond the range of air-defense systems.

The British "V-bombers," introduced in the 1950s, comprised the Vickers Valiant, Handley Page Victor, and Avro Vulcan. These served as the backbone of Britain's nuclear deterrent until superseded by Polaris-missile-equipped nuclear submarines in the 1970s. The Vulcan, the first jet bomber to use the delta-wing configuration, remained in service long enough to drop conventional bombs in the Falkland Islands War.

The first Soviet jet bombers with strategic potential were the twin-engined Tupolev Tu-16 Badger (deployed in 1954) and the larger and less successful four-engined Myasishchev M-4 Bison (deployed in 1956). In 1956 the Soviets also fielded the only turboprop strategic bomber to see service, the Tu-95 Bear. A large, swept-wing aircraft powered by four huge turboprop engines with contrarotating propellers, the Tu-95 proved to have excellent performance. Like the B-52, it was adapted to maritime and cruise missile patrol after it had become obsolete as a strategic bomber.

The aircraft mentioned above were capable of only subsonic speeds. The first operational supersonic bomber was the delta-winged Convair B-58 Hustler of the United States. Placed in active service in 1960, this bomber carried its nuclear weapon and most of its fuel in a huge, jettisonable pod beneath the fuselage.

3.10.5.3.2 Low-level penetration.

The B-58 had a service life of only three years, because in the early 1960s it became apparent that surface-to-air missiles could shoot down aircraft even at previously safe altitudes of over 50,000 feet. In response, bombers sought protection from early-warning radar by flying at low levels, and a new generation of high-performance bombers came into service that took complete advantage of the propulsion, aerodynamic, and electronic advances of the postwar era. The first of these was the U.S. General Dynamics F-111, the first operational aircraft to use a variable-sweep wing. Variable geometry was originally intended to allow the F-111 to combine the missions of low-altitude bomber and high-altitude fleet-defense fighter, but the fighter version was eventually abandoned. After a poor showing in Indochina in 1968, the F-111 became a successful high-speed, low-altitude, all-weather penetrator. As such, it joined with considerable effect in the final stages of the U.S. aerial offensive on North Vietnam, and it was also assigned to NATO as a tactical-range nuclear weapons carrier. The Soviet Su-24 Fencer was similar to the F-111.

Larger strategic bombers using variable geometry to achieve high performance at low altitudes included the Soviet Tu-26 Backfire, the U.S. Rockwell International B-1, and the Tu-160 Blackjack. These bombers, supplementing the older purely subsonic aircraft, formed an important part of the U.S. and Soviet nuclear forces after their deployment in 1975, 1985, and 1988, respectively. In common with all first-line combat aircraft, they were equipped with sophisticated electronic countermeasure (ECM) equipment designed to jam or deceive enemy radars. They could deliver free-fall conventional or nuclear bombs, air-to-surface missiles, and cruise missiles. The B-1B version could achieve supersonic flight only in short bursts at high altitude, while the Soviet bombers were capable of supersonic "dash" at low level and could fly at twice the speed of sound at high altitude.

3.10.5.4 Stealth.

3.10.5.4.1 The first operational craft.

The existence of a Stealth program, designed to produce aircraft that were effectively immune to radar detection at normal combat ranges, was announced by the U.S. government in 1980. The first aircraft employing this technology, the single-seat Lockheed F-117A ground-attack fighter, became operational in 1983. The second was the Northrop B-2 strategic bomber, which first flew in 1989. Both aircraft had unconventional shapes that were designed primarily to reduce radar reflection. The B-2 was of a flying-wing design that made it only slightly longer than a fighter yet gave it a wingspan approaching that of the B-52, while the F-117A had a short, pyramid-shaped fuselage and sharply swept wings.

3.10.5.4.2 Stealth technology.

Ever since radar-directed defenses began taking a toll of bomber formations in World War II, aircraft designers and military aviators had sought ways to avoid radar detection. Many materials of the early jet age were known to absorb radar energy rather than reflect it, but they were heavy and not strong enough for structural use. It was not until after the 1960s and '70s, with the development of such materials as carbon-fibre composites and high-strength plastics (which possessed structural strength as well as being transparent or translucent to radar), that radar signature reduction for piloted combat aircraft became possible.

Reducing radar signature also required controlling shape, particularly by avoiding right angles, sharp curves, and large surfaces. In order to direct radar energy in the least revealing directions, the external shape of a stealth aircraft was either a series of complex, large-radius, curved surfaces (as on the B-2) or a large number of small, flat, carefully oriented planes (as on the F-117A). Fuel and ordnance were carried internally, and engine intakes and exhausts were set flush or low to the surface. To avoid interception of radar emissions, stealth aircraft had to rely on inertial guidance or other nonemitting navigational systems. Other possibilities included laser radar, which scanned the ground ahead of the craft with a thin, almost undetectable laser beam.

To escape detection in the infrared spectrum, stealth aircraft were not equipped with large, heat-producing afterburner engines. This rendered them incapable of supersonic flight. Also, the shapes and structures optimal for stealth aircraft were often at odds with aerodynamic and operational requirements. Since all weaponry had to be carried internally, ordnance loads were less than for equivalent conventional aircraft, and sophisticated artificial stabilization and control systems were needed to give stealth aircraft satisfactory flying characteristics. Unlike the fighter, the B-2 had no vertical fin stabilizers, relying on flaps on the trailing edge of its notched wing to control roll, pitch, and yaw.

3.10.5.5 Other military aircraft.

3.10.5.5.1 Transport.

The success of the C-47 and C-54 in World War II inspired the development of specialized military freighters with nose- and tail-loading features, roller conveyors on the floor, and built-in winches. These permitted the quick loading of vehicles and large equipment as well as their air-dropping by parachute. Military transports ranged from small V/STOL liaison aircraft and modified versions of civilian transports to huge craft such as the Lockheed C-5 Galaxy, designed in the 1960s to carry two M-60 tanks, 16 three-quarter-ton trucks, or 245 troops. After its introduction in 1969, the C-5 was the largest aircraft in the world for almost two decades, until it was surpassed by the Soviet Antonov An-225. With a cargo bay 21 feet wide, 14.5 feet high, and 140 feet long, the An-225 was designed to carry a payload of as much as 440,800 pounds.

3.10.5.5.2 Reconnaissance.

Reconnaissance aircraft also carried ECM devices and relied heavily on electronic and infrared sensors to supplement their film cameras. Their tasks were to locate and photograph targets, using radar and conventional photographic techniques, and to probe enemy electronic defense systems to discover and evaluate the types of radio and radar equipment that were in use. They did this by offshore patrols just outside territorial limits and, more rarely, by overflights. The best-known American types used for overflights were two Lockheed aircraft -- the U-2, first flown in the mid-1950s, and the SR-71 Blackbird, which came into service in the mid-1960s. The U-2, built of aluminum and limited to subsonic flight, could cruise above 70,000 feet for very long periods. The SR-71 had a titanium airframe to resist the heat generated by flying at Mach 3; this aircraft could operate above 80,000 feet.

3.10.5.5.3 Airborne early warning.

Carrier-based early-warning aircraft had a large radar to detect aircraft or ships; some could also control interceptor fighters defending the fleet. This kind of airborne warning and control system (AWACS) airplane appeared in land-based air forces to detect low-flying enemy raiders and direct interceptors toward them. The first aircraft of this type was a Soviet turboprop, the Tu-126 Moss, which was succeeded in the 1980s by the jet-powered Ilyushin Il-76 Mainstay. These craft, like the U.S. E-3 Sentry (a converted Boeing 707), carried a large, saucer-shaped radar on the fuselage. Britain's early-warning aircraft was the British Aerospace Nimrod. (see also aviation)

3.10.5.6 Helicopters.

The helicopter had its first significant impact on military operations during the Korean War, but it came of age in Vietnam. Helicopters fielded air-mobile infantry units, evacuated casualties, hauled artillery and ammunition, rescued downed aviators, and served as ground-attack craft. Helicopters became serious operational machines only after American manufacturers fitted them with gas-turbine engines, which were much less sensitive than piston engines to high temperatures and low atmospheric density, had far greater power-to-weight ratios, and occupied considerably less space.

3.10.5.6.1 Assault and attack helicopters.

The mainstay of U.S. Army assault units in Vietnam was the Bell UH-1 Iroquois, popularly known as the Huey. As early as 1962, army aviators added turret-mounted automatic 40-millimetre grenade launchers, skid-mounted rocket pads, and remotely trainable 7.62-millimetre machine guns. These experiments, which proved effective in supporting helicopter assault operations, led to the AH-1G HueyCobra, deployed in 1967 as the first purpose-built helicopter gunship. With its pilot seated behind and above the gunner, the HueyCobra pioneered the tandem, stepped-up cockpit configuration of future attack helicopters.

After the Vietnam War, the lead in gunship design passed to the Soviet Union, which, in the Afghan War of the 1980s, fielded the Mil Mi-24 Hind, the fastest and possibly most capable helicopter gunship of its time. A primary role of the Hind was to attack armoured vehicles; to this end, it mounted guided antitank missiles on stub wings projecting from the fuselage. In addition to the two-man cockpit configuration of the HueyCobra, it had a small passenger and cargo bay that gave it a limited troop-transport capability.

The successor to the HueyCobra was the McDonnell Douglas AH-64 Apache, a heavily armoured antiarmour helicopter with less speed and range than the Hind but with sophisticated navigation, ECM, and fire-control systems. The Apache became operational in 1986. Soon afterward the Soviets produced the Mi-28 Havoc, a refinement of the Hind that, with no passenger bay, was purely a gunship. (see also attack aircraft)

3.10.5.6.2 Naval helicopters.

Helicopters were used extensively in antisubmarine roles, "dipping" sonar sensors into the water to locate their targets and launching self-homing torpedoes to destroy them. Ship-borne helicopters also served as firing platforms for antiship missiles and were used to carry warning and surveillance radars, typically sharing information with their mother ships. By firing heat-producing or chaff flares to confuse infrared and radar homing systems, naval helicopters could serve as decoys for antiship missiles. (see also naval aircraft)

3.10.5.7 Remotely piloted vehicles.

The first remotely piloted vehicles (RPVs) were small, pilotless aircraft controlled by command radio transmission. Most of these fell into one of two categories: extremely high-performance drones used to test new systems; and small, relatively inexpensive drones used for training. Both were typically reusable, being recovered by radio-controlled landing or, more commonly, by parachute. Target drones were commonly fitted with radar reflectors to stimulate the radar return of enemy aircraft, and it soon occurred to strategists to use them as decoys to assist bombers in penetrating enemy defenses. That modified target drones might be effective platforms for communications relay and for sensor and reconnaissance systems also became evident. The Ryan QM-34 Firebee, a photoreconnaissance modification of a standard U.S. target drone, saw extensive service in Vietnam. A swept-wing, turbojet-powered subsonic vehicle less than half the size of a jet fighter, the Firebee penetrated heavily defended areas at low altitudes with impunity by virtue of its small radar cross section and brought back strikingly clear imagery. Indicative of later development was the Boeing Compass Cope, a long-winged, subsonic, turbofan-powered drone capable of long flights at extremely high altitudes. ( J.W.R.T./J.F.G.) (see also reconnaissance aircraft, fighter aircraft )