Important development occurred in civil engineering in the first half of the 20th century, although there were few striking innovations. Advancing techniques for large-scale construction produced many spectacular skyscrapers, bridges, and dams all over the world but especially in the United States. The city of New York acquired its characteristic skyline, built upon the exploitation of steel frames and reinforced concrete. Conventional methods of building in brick and masonry had reached the limits of feasibility in the 1800s in office blocks up to 16-stories high, and the future lay with the skeleton frame or cage construction pioneered in the 1880s in Chicago. The vital ingredients for the new tall buildings or skyscrapers that followed were abundant cheap steel—for columns, beams, and trusses—and efficient passenger elevators. The availability of these developments and the demand for more and more office space in the thriving cities of Chicago and New York caused the boom in skyscraper building that continued until 1931, when the Empire State Building, with its total height of 1,250 feet (381 metres) and 102 stories, achieved a limit not exceeded for 40 years and demonstrated the strength of its structure by sustaining the crash impact of a B-25 bomber in July 1945 with only minor damage to the building. The Great Depression brought a halt to skyscraper building from 1932 until after World War II.

Concrete, and more especially reinforced concrete (that is, concrete set around a framework or mesh of steel), played an important part in the construction of the later skyscrapers, and this material also led to the introduction of more imaginative structural forms in buildings and to the development of prefabrication techniques. The use of large concrete members in bridges and other structures has been made possible by the technique of prestressing: by casting the concrete around stretched steel wires, allowing it to set, then relaxing the tension in the wires, it is possible to induce compressive stresses in the concrete that offset the tensile stresses imposed by the external loading, and in this way the members can be made stronger and lighter. The technique was particularly applicable in bridge building. The construction of large-span bridges received a setback, however, with the dramatic collapse of the Tacoma Narrows (Washington) Suspension Bridge in the United States in 1940, four months after it was completed. This led to a reassessment of wind effects on the loading of large suspension bridges and to significant improvements in subsequent designs. Use of massed concrete has produced spectacular high arch dams, in which the weight of water is transmitted in part to the abutments by the curve of the concrete wall; such dams need not depend upon the sheer bulk of impervious material as in a conventional gravity or embankment dam.

Transportation

Some of the outstanding achievements of the 20th century are provided by transportation history. In most fields there was a switch from steam power, supreme in the previous century, to internal combustion and electricity. Steam, however, retained its superiority in marine transport: the steam turbine provided power for a new generation of large ocean liners beginning with the Mauretania, developing 70,000 horsepower and a speed of 27 knots (27 nautical miles, or 50 km, per hour) in 1906 and continuing throughout the period, culminating in the Queen Elizabeth, launched in 1938 with about 200,000 horsepower and a speed of 28.5 knots. Even here, however, there was increasing competition from large diesel-powered motor vessels. Most smaller ships adopted this form of propulsion, and even the steamships accepted the convenience of oil-burning boilers in place of the cumbersome coal burners with their large bunkers.

On land, steam fought a long rearguard action, but the enormous popularity of the automobile deprived the railways of much of their passenger traffic and forced them to seek economies in conversion to diesel engines or electric traction, although these developments had not spread widely in Europe by the outbreak of World War II. Meanwhile, the automobile stimulated prodigious feats of production. Henry Ford led the way in the adoption of assembly-line mass production; his spectacularly successful Model T, the “Tin Lizzie,” was manufactured in this way first in 1913, and by 1923 production had risen to nearly two million per year. Despite this and similar successes in other countries, the first half of the 20th century was not a period of great technological innovation in the motorcar, which retained the main design features given to it in the last decade of the 19th century. For all the refinements (for example, the self-starter) and multitudinous varieties, the major fact of the automobile in this period was its quantity.

The airplane is entirely a product of the 20th century, unlike the automobile, to which its development was intimately related. This is not to say that experiments with flying machines had not taken place earlier. Throughout the 19th century, to go back no further, investigations into aerodynamic effects were carried out by inventors such as Sir George Cayley in England, leading to the successful glider flights of Otto Lilienthal and others. Several designers perceived that the internal-combustion engine promised to provide the light, compact power unit that was a prerequisite of powered flight, and on December 17, 1903, Wilbur and Orville Wright in their Flyer I at the Kill Devil Hills in North Carolina achieved sustained, controlled, powered flight, one of the great “firsts” in the history of technology. The Flyer I was a propeller-driven adaptation of the biplane gliders that the Wright brothers had built and learned to fly in the previous years. They had devised a system of control through elevator, rudder, and a wing-warping technique that served until the introduction of ailerons. Within a few years the brothers were flying with complete confidence, astonishing the European pioneers of flight when they took their airplane across the Atlantic to give demonstrations in 1908. Within a few months of this revelation, however, the European designers had assimilated the lesson and were pushing ahead the principles of aircraft construction. World War I gave a great impetus to this technological development, transforming small-scale scattered aircraft manufacture into a major industry in all the main belligerent countries, and transforming the airplane itself from a fragile construction in wood and glue into a robust machine capable of startling aerobatic feats.

The end of the war brought a setback to this new industry, but the airplane had evolved sufficiently to reveal its potential as a medium of civil transport, and during the interwar years the establishment of transcontinental air routes provided a market for large, comfortable, and safe aircraft. By the outbreak of World War II, metal-framed-and-skinned aircraft had become general, and the cantilevered monoplane structure had replaced the biplane for most purposes. War again provided a powerful stimulus to aircraft designers; engine performance was especially improved, and the gas turbine received its first practical application. Other novel features of these years included the helicopter, deriving lift from its rotating wings, or rotors, and the German V-1 flying bomb, a pilotless aircraft.

The war also stimulated the use of gliders for the transport of troops, the use of parachutes for escape from aircraft and for attack by paratroops, and the use of gas-filled balloons for antiaircraft barrages. The balloon had been used for pioneer aeronautical experiments in the 19th century, but its practical uses had been hampered by the lack of control over its movements. The application of the internal-combustion engine to a rigid-frame balloon airship by Ferdinand von Zeppelin had temporarily made a weapon of war in 1915, although experience soon proved that it could not survive in competition with the airplane. The apparently promising prospects of the dirigible (that is, maneuverable) airship in civil transport between the wars were ended by a series of disasters, the worst of which was the destruction of the Hindenburg in New Jersey in 1937. Since then the airplane has been unchallenged in the field of air transport.

Communications

The spectacular transport revolution of the 20th century was accompanied by a communications revolution quite as dramatic, although technologically springing from different roots. In part, well-established media of communication like printing participated in this revolution, although most of the significant changes—such as the typewriter, the Linotype, and the high-speed power-driven rotary press—were achievements of the 19th century. Photography was also a proved and familiar technique by the end of the 19th century, but cinematography was new and did not become generally available until after World War I, when it became enormously popular.

The real novelties in communications in the 20th century came in electronics. The scientific examination of the relationship between light waves and electromagnetic waves had already revealed the possibility of transmitting electromagnetic signals between widely separated points, and on December 12, 1901, Guglielmo Marconi succeeded in transmitting the first wireless message across the Atlantic. Early equipment was crude, but within a few years striking progress was made in improving the means of transmitting and receiving coded messages. Particularly important was the development of the thermionic valve, a device for rectifying (that is, converting a high-frequency oscillating signal into a unidirectional current capable of registering as a sound) an electromagnetic wave. This was essentially a development from the carbon-filament electric lightbulb. In 1883 Edison had found that in these lamps a current flowed between the filament and a nearby test electrode, called the plate, if the electric potential of the plate was positive with respect to the filament. This current, called the Edison effect, was later identified as a stream of electrons radiated by the hot filament. In 1904 Sir John Ambrose Fleming of Britain discovered that by placing a metal cylinder around the filament in the bulb and by connecting the cylinder (the plate) to a third terminal, a current could be rectified so that it could be detected by a telephone receiver. Fleming’s device was known as the diode, and two years later, in 1906, Lee De Forest of the United States made the significant improvement that became known as the triode by introducing a third electrode (the grid) between the filament and the plate. The outstanding feature of this refinement was its ability to amplify a signal. Its application made possible by the 1920s the widespread introduction of live-voice broadcasting in Europe and America, with a consequent boom in the production of radio receivers and other equipment.

This, however, was only one of the results derived from the application of the thermionic valve. The idea of harnessing the flow of electrons was applied in the electron microscope, radar (a detection device depending on the capacity of some radio waves to be reflected by solid objects), the electronic computer, and in the cathode-ray tube of the television set. The first experiments in the transmission of pictures had been greeted with ridicule. Working on his own in Britain, John Logie Baird in the 1920s demonstrated a mechanical scanner able to convert an image into a series of electronic impulses that could then be reassembled on a viewing screen as a pattern of light and shade. Baird’s system, however, was rejected in favour of electronic scanning, developed in the United States by Philo Farnsworth and Vladimir Zworykin with the powerful backing of the Radio Corporation of America. Their equipment operated much more rapidly and gave a more satisfactory image. By the outbreak of World War II, television services were being introduced in several countries, although the war suspended their extension for a decade. The emergence of television as a universal medium of mass communication is therefore a phenomenon of the postwar years. But already by 1945 the cinema and the radio had demonstrated their power in communicating news, propaganda, commercial advertisements, and entertainment.

Military technology

It has been necessary to refer repeatedly to the effects of the two World Wars in promoting all kinds of innovation. It should be observed also that technological innovations transformed the character of war itself. One weapon developed during World War II deserves a special mention. The principle of rocket propulsion was well known earlier, and its possibilities as a means of achieving speeds sufficient to escape from Earth’s gravitational pull had been pointed out by such pioneers as the Russian Konstantin Tsiolkovsky and the American Robert H. Goddard. The latter built experimental liquid-fueled rockets in 1926. Simultaneously, a group of German and Romanian pioneers was working along the same lines, and it was this team that was taken over by the German war effort in the 1930s and given the resources to develop a rocket capable of delivering a warhead hundreds of miles away. At the Peenemünde base on the island of Usedom in the Baltic, Wernher von Braun and his team created the V-2. Fully fueled, it weighed 14 tons; it was 40 feet (12 metres) long and was propelled by burning a mixture of alcohol and liquid oxygen. Reaching a height of more than 100 miles (160 km), the V-2 marked the beginning of the space age, and members of its design team were instrumental in both the Soviet and U.S. space programs after the war.

Technology had a tremendous social impact in the period 1900–45. The automobile and electric power, for instance, radically changed both the scale and the quality of 20th-century life, promoting a process of rapid urbanization and a virtual revolution in living through mass production of household goods and appliances. The rapid development of the airplane, the cinema, and radio made the world seem suddenly smaller and more accessible. In the years following 1945 the constructive and creative opportunities of modern technology could be exploited, although the process has not been without its problems.