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Top 20 Greatest Achievements of the 20th Century

The Greatest Engineering Achievements of the 20th Century is a collaborative project led by the National Academy of Engineering. The achievements, nominated by 29 professional engineering societies, were selected and ranked by a distinguished panel of the nation’s top engineers. This is the first of five articles highlighting the top 20 achievements.


Widespread use of electric power has been one of the greatest sources of social change in the 20th century. It changed the face of cities in terms of growth and population, helped farmers increase production through labor-saving machinery, and contributed to a more highly educated populace, liberated from the drudgery of manual chores and labor.

The average person in 1900 awoke to a hand-wound clock. In an era of kerosene lamps and lanterns, outhouses and manual water pumps, there was no radio or TV for local or world news, and preparing for the day involved getting coal or wood for the kitchen stove, using hand-tools to prepare food. Farmers had no electric motors or machinery to milk cows or process grain.

Thomas Edison’s work had led to the first commercial power plant for incandescent lighting and power in 1882. However, Edison’s system used direct current (DC), which could only be profitably distributed in a limited area around the generating station. The work of engineers such as Nikola Tesla and Charles Steinmetz led to the successful commercialization of alternating current (AC), which enabled transmission of high-voltage power over large distances.

Prime movers in power stations evolved from water wheels to dams with a variety of turbines. Each design innovation met the burgeoning needs of an increasingly industrial society.

To make electricity affordable, the Rural Electric Administration instituted innovations that included standardized designs for distribution lines, mass production and construction techniques, system protection, and wide area distributed power planning. Construction costs plummeted from $2,000 per line mile at the beginning of the project to less than $600 by 1939.

The electric power grid system continues to develop with a movement to interconnect grids into huge national or international networks. By the 1990s, the United States was linked into two giant grid systems, each serving half of the country. This allows power produced in one state to be used thousands of miles away. Indeed, transmission techniques have now come full circle, with a return to DC transmission at high voltage. Made possible with semiconductor switches, the use of long-range DC transmission is just beginning — one of many technologies that hold promise in bringing further advantages in economy and reliability.

.Water Supply & Distribution

Today, a simple turn of the tap provides clean water — a precious resource. Engineering advances in managing this resource changed life profoundly in the 20th century, virtually eliminating waterborne diseases in developed nations, and providing clean and abundant water for communities, farms and industries.

At the outset of the century, waterborne diseases like typhoid fever and cholera were scourges across America. Typhoid alone killed more than 150 per 100,000 people annually. Dysentery and diarrhea, the most common waterborne diseases, were the third largest cause of death in the nation.

In 1900, it was common practice to dispose of garbage and raw sewage by dumping it into streets, alleys and waterways. Industrial waste was dumped into the nation’s waterways. Few municipalities treated wastewater because it was widely believed that running water purified itself. Outhouses and wells were common in rural areas. In urban areas, an average tenement housed two thousand people, but not one bathtub. Most large cities built public baths.

Disinfection with chlorine was under way in 1908. By 1918, over 1000 cities treating 3 billion gallons of water a day were enjoying the increased health benefits of chlorine disinfection. As a result, the major water-borne diseases ceased to exist in the United States by World War II.

Early in the century, engineers developed techniques to treat municipal and industrial wastewater, and new ways to treat water are continually being developed. Engineers have also developed sensitive and accurate instrumentation that can analyze water for carcinogens at parts per trillion levels. As a result, the EPA has greatly lowered the levels of allowable chemicals in wastewater.

An adequate supply of water often depends on the building of dams, reservoirs, and aqueducts. Today, storage and distribution systems enable semi-arid and arid regions to store water for later use during periods of high precipitation. They have also enabled people to move from large cities to suburban communities and helped those dependent on wells.

Quantity and quality are the ongoing challenges for engineers. The World Bank estimates that currently more than a billion people — 1/6 of the world’s population — do not have access to an adequate supply of water. Another concern for the future is the increase in global desertification. The world’s dry lands already make up about 40 percent of Earth’s land surface. Expansion can lead to loss of farmlands, mass migrations, loss of economic activities, and disaster for many.

The transfer of engineering knowledge to ensure safe water supplies through the collection, treatment and distribution of surface, ground and wastewater is imperative for the continued economic growth and development of nations in the 21st century.


The automobile may be the ultimate symbol of personal freedom. In 1900 the average American traveled about 1200 miles in a lifetime, mostly on foot, and mostly within his or her own village or town. By the end of the century, the typical American adult would travel some 12,000 miles by automobile alone, in just one year.

In 1900 a typical automobile was shaped like a box, much like a horseless carriage, with little protection from rain, dust or other hazards. It was started by a hand-crank. Engines were mounted haphazardly under the body, and steering was often by tiller. All of the parts were exposed to the elements. The arrival of pneumatic tires made the ride more comfortable, but punctures every 10 or 20 miles were the norm. Kerosene side lamps and smelly acetylene head lamps lit the traveler’s way. People who drove autos in the early days were seen as heroic adventurers.

By 1900 there were 50 automobile-manufacturing companies and some 8,000 cars registered in the United States. Each car was hand-made and cost about $1,550. With an average wage of $12.74 per week, only the wealthy could afford cars.

Engineering milestones included the electric starter in 1911; the synchronized transmission for easier gear shifting; improved carburetors; heaters; mechanically operated windshield wipers; and interchangeable parts.

The 1930s saw more reliable braking, higher-compression engines and the world’s first diesel engine by Mercedes. Automobile engines were becoming larger, and many had 12 and 16 cylinders. Independent front suspension was added to make larger cars more comfortable.

Large-scale production began in the early 1950s. New automotive features included air conditioning, electrically operated car windows, seat adjusters, and a change from a 6-volt to a 12-volt ignition system to improve engine performance. Cars increased in size and weight, but power steering and brakes made them easier to handle.

In 1900 a car might have a total of 100 parts, while today it has some 14,000. Design innovations incorporate breakthroughs in computerization, high-strength plastics, and alloys of steel and nonferrous metals.

As for changing social patterns, a historian has said that Henry Ford freed common people from the limitations of geography, creating social mobility on a scale previously unknown


It wasn’t until 1908, when Orville Wright successfully flew for an hour, that the world began to take flight seriously.
Patent conflicts between the Wright brothers and Glenn Curtiss limited the development of aviation technology in the United States until World War I. Numerous innovations in materials and design were needed quickly. Flammable plywood and fabric were soon replaced with metals like iron and welded steel tubing, and wings were streamlined. Anthony Fokker refined the design of maneuverable triplanes and developed the interrupter gear that synchronized machine gun fire with the spinning propeller, thus giving Germans air superiority in 1916.

The Allies countered with more powerful engines and shifted manufacturing techniques in other industries to the production of aircraft. During this period, thousands of aircraft were produced by both sides. Many were untested planes, quickly and prematurely pressed into service, which often broke apart in the air. Given the short history of aviation, most pilots were grossly inexperienced. Both factors left a legacy of fatal mishaps and a resolve to explore more sophisticated aviation techniques.

The war proved that airplanes could be easily adapted for civilian uses, transporting mail, passengers, and cargo. The DC-3 made its first appearance in 1935 and represented a major leap forward in airplane development, proving airline travel economically practical. It incorporated the technical advances of the day, including metal skin; an internally instead of externally braced design; an almost completely enclosed engine that reduced drag; the addition of wing flaps, and variable-pitch propellers.

Working independently, Sir Frank Whittle in England and Hans von Ohain in Germany developed the gas turbine in 1939. This signaled the beginning of jet transport.

After World War II, a return to building passenger and cargo planes continued on a worldwide scale. “Bigger, better, faster” was the slogan that drove production.

Today, aviation accounts for some 600,000 pilots in the United States. Airports, once grassy fields with wooden shacks for terminals, are now major architectural statements. Aviation activities and related services account for more than 6 percent of the nation’s gross domestic product.

As we contemplate what the next century of flight will bring, Orville Wright’s early prediction seems appropriate. He said, “I cannot answer except to assure you it will be spectacular.”