The advantages of discharging missiles from a height were understood from the dawn of time, and appreciation of the military potential of aerial weaponry predated human-carrying flying vehicles. Visionary schemes foresaw destruction raining down from balloons, and Austrian forces suppressing a rebellion actually attacked Venice with unmanned balloons carrying incendiary bombs in 1849.
But as a practical matter, aerial weaponry had to await the development of the airplane and dirigible. Rifles and machine guns were carried aloft almost from the beginning and were used with limited effect by Italian aviators against Ottoman forces in Libya in 1911. The Italians also dropped crude bombs, which showed more promise.
Aerial weaponry came of age during
World War I, following a brief period in which aircraft were used almost exclusively for
reconnaissance; the aviators defended themselves with pistols and rifles. Pusher aircraft, with the crew seated ahead of the engine and propeller for a clear forward field of fire, were armed with machine guns even before the war, but these airplanes were slower than "tractor" scouts with forward-mounted engines. The seminal event, the development of synchronization gear, made it possible to mount a machine gun to fire through the propeller arc ahead of the pilot, making the entire aircraft a gun mount and vastly simplifying aiming. Defensive machine guns on flexible mounts soon followed. Machine gun-armed aircraft were used to strafe ground troops, and from 1917, the Germans and then the Allies fielded specialized ground-attack aircraft. After experiments with steel flechettes, highly explosive bombs fitted with fins and impact fuses became the staple of aerial bombardment. In 1915, the Germans launched zeppelins capable of carrying two tons of bombs, and by war's end the largest conventional bombers carried bomb loads of more than a ton. Such aircraft, however, were exceptional, and primitive aiming and navigation systems limited their effectiveness. Zeppelin raids were briefly effective as a terror weapon, and attacks on London by conventional bombers in 1917 forced the British to hold back large numbers of aircraft from the Western Front for defense—but bombing had little effect on the war. Aerial reconnaissance, artillery spotting, and denying the enemy use of the air remained far more important than bombardment. Techniques and technologies developed in World War I reached maturity during the interwar period and played important roles in
World War II, notably dive-bombing, torpedo attacks on ships, and cannon- and rocket-armed fighters. On fighters, ring-and-bead gun sights gave way to an illuminated display projected on a ground glass plate in front of the pilot, controlled by a gyroscopic mechanism that automatically computed the lead angle; these would revolutionize air-to-air combat by making average fighter pilots adequate marksmen.
In 1918, rifle-caliber machine guns were the standard aircraft armament—twin synchronized guns on fighters for attack and manually aimed flexible guns for defense. By 1939-1940, British fighters carried as many as eight rifle-caliber machine guns, the Americans were standardizing .50-caliber weapons, German fighters carried 20-mm shell-firing cannon, and newer American and British bombers had hydraulic and electrically powered multiple-gun turrets. Radar, first used to direct ground-controlled intercepts of attacking bombers and then mounted in night fighters and bombers to permit attacks in darkness and through clouds, completely reshaped the face of aerial warfare from 1940 to 1945.
Ground and naval forces proved vulnerable to aerial attack from the beginning of World War II, and air superiority became an essential ingredient of victory. Carrier-based dive-bombers and torpedo-bombers replaced the guns of capital ships as arbiters of naval combat. Fighters carried heavier cannon; rockets supplemented guns for ground attack and, in German service, for attacks on bomber formations. German aircraft dropped radio-controlled, visually guided bombs and missiles in attacks on ships from 1943, and the Americans used radio-controlled bombs against bridges in 1944-1945. American forces introduced napalm (jellied gasoline) firebombs as an antipersonnel weapon.
Advances in aircraft speed, range, and load-carrying capability made long-range aerial bombardment a major factor in World War II, although problems in accuracy and navigation had to be solved before attacks on cities, transportation nets, and industry could have strategic impact. The destruction by firestorm of Guernica at the hands of German and Italian bombers in the
Spanish civil war provided a foretaste of the vulnerability of cities to incendiary bombs. Japanese attacks on Chinese cities from 1937 and German raids during the
Battle of Britain hinted at the potential of long-range strategic bombardment; however, only the British Royal Air Force and the U.S. Army Air Forces realized that potential, and then not until 1943-1945. By war's end, heavy bombers routinely carried two to seven tons of bombs, and the British on occasion employed enormous bombs of twelve thousand and twenty-two thousand pounds, known as "blockbusters." The defining expression of strategic bombardment came with the atomic bombs, which destroyed Hiroshima and Nagasaki in August 1945, though, ironically, incendiary attacks on cities—notably Hamburg, Dresden, and Tokyo—caused far more deaths.
The appearance of jet aircraft late in World War II introduced unprecedented speed to aerial combat, demanding air-to-air weapons with increased range and single-shot lethality. In response, guided missiles began to enter service in the middle to late 1950s. The first to achieve combat success was the U.S. Navy's heat-seeking Sidewinder in 1958; with progressive improvements, it remains in service. Radar-guided missiles offered the advantage of being able to attack through clouds, but they were more complex than heat-seekers and took longer to mature technically. The replacement of vacuum tubes with transistors from the 1970s in the West—but, significantly, not in the Soviet Union—enormously improved reliability and introduced an ongoing revolution in miniaturization. The first heat-seekers homed in on engine heat and flew up the tailpipe to achieve a kill; current infrared missiles are all-aspect—that is, they can acquire the target from the front or sides as well as from the rear, homing in on the jet exhaust plume and using sophisticated lead-computing gyros to determine target location and laser proximity fuses to detonate the warhead.
Radar missiles have undergone comparable improvement and now encompass several basic types, each with its particular advantages: active homing missiles, which carry their own transmitters and receivers; semiactive homing missiles, which carry only a receiver and depend on the launching aircraft's radar to illuminate the target; and passive homing missiles, which lock onto enemy radar transmissions. Active missiles operate autonomously once launched, that is, they require no external commands, but are comparatively large and complex. Semiactive missiles are smaller and simpler, but require the launching aircraft to continue transmitting and remain pointed generally toward the target until missile impact. Passive radar missiles operate autonomously, but can home in only so long as the enemy radar is transmitting. Active radar homing is widely used in antiship missiles, often with infrared terminal homing. Semiactive radar missiles are the most common type of air-to-air missile next to infrared. Passive radar missiles are widely used to attack radar-controlled, surface-based antiaircraft guns and missiles.
Air-to-ground weaponry was revolutionized by the development in the United States of television, laser, and autonomously guided aerial munitions in the late 1960s. These munitions proved enormously effective in destroying discrete targets such as bridges and power plants late in the
Vietnam War. The lesson was reinforced in the
Gulf War of 1990-1991. Although laser-guided bombs took most of the plaudits in the Persian Gulf, autonomously guided Tomahawk cruise missiles, using on-board, terrain-mapping radar for orientation, demonstrated that air-breathing cruise missiles could evade sophisticated antiaircraft defenses and inflict significant damage on small, high-value targets.
More exotic aerial weapons include aerially sprayed defoliants, used extensively by the United States in Vietnam; fuel-air bombs, in which an aerosol-sprayed explosive agent such as butane detonates in combination with atmospheric oxygen; and aerially dispensed microtoxins, highly lethal organisms related to fungi, used by Soviet and Soviet client forces in the Middle East and Southeast Asia.
Christopher Campbell, Air Warfare: The Fourth Generation (1984); Charles H. Gibbs-Smith, Aviation: An Historical Survey from Its Origins to the End of World War II (1970); John H. Morrow, Jr., The Great War in the Air: Military Aviation from 1909 to 1921 (1993).