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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 fifth and final article highlighting the top 20 achievements. Source:

Top 20 Greatest Engineering Achievements,
Seventeen through Twenty

     Petroleum-based fuels have increased agricultural productivity, provided the means for distributing industrial and farm products, and furnished the personal mobility that defines 20th century technology. Petrochemicals also have had an enormous impact, providing everything from aspirin to zippers, including pharmaceuticals, medical devices, synthetic fabrics, fertilizers, pesticides, building materials and cosmetics.

     Until 1900, refining consisted of a fairly simple batch process whereby oil was heated until it vaporized, and the various fractions were separated by distillation. In 1913, thermal cracking was introduced. Catalytic cracking began in 1936. Cracking of petroleum yields light oils, heavier oils, and gases such as methane, ethane, ethylene, propane and propylene.

     In 1947, a process called “platforming” introduced platinum as a catalyst in the refining process. This resulted in fewer emissions, removed much of the sulfur and other contaminants, and generated significant amounts of hydrogen and other raw materials used to manufacture plastics.

     At the beginning of the century, crude oil production worldwide was nearly 150 million barrels. Half of this total was produced in Russia. Annual production surpassed 1 billion barrels in 1925 and 2 billion barrels in 1940. By the end of the 20th century, there were almost 1 million wells in more than 100 countries producing more than 20 billion barrels per year. An estimated 77 percent of the world’s total recoverable oil has already been discovered.

     The petroleum-refining industry has taken remedial action to address environmental problems. Effluent water and atmospheric emission of hydrocarbons and combustion products have been reduced. Techniques have been developed for manufacturing high-quality gasoline without using lead additives.

      Much research has examined alternatives to petroleum-based fuels. Since the crude oil shortages of the late 1960s and early 1970s, the natural gas formed alongside or near oil deposits became itself an important world energy source.

      The engineering efforts in the petroleum and gas industries continue to resolve environmental issues, dealing with shortages and spills alike. If, as anticipated with any limited resource, oil reigns as the dominant source of energy for a mere transitory period of 100 years or so, then it will have done so with enormous influence on the quality of life worldwide.

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     At the beginning of the 20th century, communications relied on mail, the telegraph and the telephone. News did not travel quickly. At the close of the century, people can’t imagine such slow, plodding ways to communicate.

     Today, tiny semiconductor lasers routinely transmit light pulses carrying billions of bits of information per second over glass fibers. This process has made worldwide connection—by phone, fax or the Internet—almost instantaneous.

     In the 1940s and early 1950s, Charles Townes and Arthur Schawlow were deeply interested in the field of microwave spectroscopy, a field that delved into the characteristics of molecules. They were eager to use microwave radiation of short wavelengths, because as the wavelengths became shorter, the interaction with molecules became stronger. In the fall of 1957 they began working out the principles of a device that could provide these shorter wavelengths. The paper they published in 1958, which laid out the principles for the laser, caused an explosion of research by engineers and scientists.

     In 1960, American physicist Theodore Maiman built the first laser to successfully produce a pulse of coherent light, using synthetic ruby as the laser medium. The first continuously operating laser was achieved a few months later. Now someone had to invent a means to channel the powerful optical waves effectively.

     Glass-clad fibers were thought to be excellent for medical imaging, but not very practical for communications over long distances. Based on the work of Charles K. Kao, an engineer at Standard Telecommunications Laboratories in the United Kingdom, laboratories around the world began studying the problem.

     In 1970, Robert Maurer demonstrated the first low-loss fiber. By 1974, John MacChesney at Bell Labs introduced an alternative synthesis process leading to low contamination and precise index of refraction profiles.

     Engineers at Laser Diode Labs developed the first commercial continuous-wave semiconductor laser operating at room temperature in 1975. This opened the door to the use of lasers to transmit optically encoded telephone conversations over fiber-optic cables. In 1987 erbium-doped fiber amplifiers were introduced, which provide multiple channels of laser light and can handle 80 million telephone calls simultaneously.

     In 1988 the first transoceanic fiber cable, TAT-8, was laid. While the first trans-Atlantic copper cable cost $1 million per circuit to install in 1956, TAT-8 cost less than $10,000 per circuit.

     Aside from providing the basis for modern communications systems, the laser is a versatile tool used in many industries. It is used in manufacturing to cut precision parts, in medical applications such as eye surgery, in satellites to transmit weather and climate information, in scanners to read bar codes at cash registers and in devices to play music on compact discs.

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     The harnessing of the atom in the 1940s changed the nature of war forever, offered a new source for electrical power generation and improved medical diagnostic techniques. Nuclear technologies have stirred emotions and controversy, but the engineering achievements related to their development remain among the most important of the 20th century.

     In 1942, Enrico Fermi conducted the first controlled chain reaction, releasing energy from the atom’s nucleus. The developments that immediately followed were directed by Robert Oppenheimer, working with engineers and physicists from the Los Alamos National Laboratory in New Mexico. Their work came amid worldwide competition to be the first to have the atom bomb as a defense priority in World War II. As a destructive power the atomic bomb has been unequalled, and its potential threat alone drives peace and war initiatives worldwide.

     The first nuclear-reactor radioisotopes for civilian medical use were delivered in 1946. Both military adaptation in submarines and aircraft carriers and the use of nuclear energy for commercial power plants resulted from this work. Admiral H. G. Rickover led engineers to pioneer new materials, design reactors, establish safety and control standards and operating procedures and build and test full-scale propulsion prototypes.

     In the 1950s, nuclear development was actively pursued in Europe, resurging in the United States in the 1960s and 1970s, with Europe and the Far East having the greatest growth in activity since then. Today nuclear power is meeting the annual electrical needs of more than 1 billion people with more than 400 operating reactors worldwide. Nuclear energy accounts for about 20 percent of power production in the United States.

     Nuclear safety and efficiency have improved significantly since 1990. New generations of small, modular power plants are on the horizon. A South African utility has announced plans to market a modular gas-cooled pebble-bed reactor that does not require emergency core-cooling systems and physically cannot “melt down.” MIT and the Idaho National Engineering and Environment Lab are developing a similar design to supply high-temperature heat for industrial processes such as hydrogen generation and desalinization.

     Adoption of safe and cost-efficient nuclear energy programs, safe disposal of nuclear waste and the optimization of process design continue to require cooperative efforts among engineers on a global scale. Nuclear energy has potential as a lasting solution to energy demand, driving engineers to find solutions toward adopting nuclear and other renewable sources.

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     Much as earlier eras were characterized as the ages of stone, iron and copper, it may be that the term that best characterizes the 20th century is “the age of engineered materials.”

     But choosing just one material to define the century would be difficult. Steel for skyscrapers? Copper for electrical conduction? Silicon for chips? Plastics and polymers? Biomaterials for medical implants? In one way or another, all of these materials have been crucial to the inventions and innovations that have transformed the century.

     Adjusting carbon and other elements in steel has produced many new alloys. Adding tin to copper made bronze, ideal for gears and bearings in places where strength counts, as in industrial machinery. Additives can turn some materials into shape-shifters. For example, polyvinylchloride (PVC) used in gutters, pipes, and panels can be turned into clothing by adding plasticizers.

     More of the world’s products are made with composites that combine different types of strength or resilience. These include exotic amorphous metals and shape-memory alloys — “smart” materials that can actually respond to changes in their environment and “remember” their shape. They are being applied to many products such as stents used to keep human arteries open.

     The greatest leaps in technological innovation occurred as improved materials become available. This is especially true in the semiconductor business, where engineering silicon to make microprocessors is a delicate process. Silicon must be purified to produce crystals, and then sliced into wafer-thin chips. With recent lab-on-a-chip technologies, the ability to build and use micromachines will soon move from a curiosity to specific applications.

     At the end of World War II, the U.S. military released to the public many high-tech synthetic materials that were previously restricted or unavailable. These materials included silicones, Dacron, polyurethanes, nylon, titanium and Teflon (which was discovered purely by accident). Remarkable new biomaterials continue to be developed for use in making heart-assist devices, artificial kidneys, contact lenses, vascular grafts, shunts, sutures, prostheses and hundreds of other products.

     Fiberglass-reinforced plastics have been molded into rigid shapes to provide car bodies and hulls for small ships. Carbon fiber has demonstrated remarkable properties that make it an alternative to metals for high-temperature turbine blades. Ceramics research has produced materials resistant to high temperatures and suitable for heat shields on spacecraft. New analytical techniques, molecular and atomic imaging and quantum calculations for atomic and molecular systems are available to help optimize materials choices and manufacturing approaches.

     Materials development today is much closer to engineering science than in the past. The engineer’s ability to translate that science into applications is now approaching the level of atomic and molecular design, the frontier of the future.

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