Diesel Locomotives

Few advancements in American railroading have been as groundbreaking as the introduction of the diesel-electric locomotive. In just a few short years after World War II, diesel locomotion was seen on almost every railroad in the United States. The use of the diesel engine in World War II, showed the advancement of the diesel engine, as diesel engine were used in many maritime vessels, and proved to be reliable and easy to maintain. Diesel locomotive technology took much trial and error, as advancements had to be make in both diesel technology and electric technology.

Bob Wilcox

American railroads were quick to adopt the diesel locomotive because of their operational similiarities. Electric locomotives were introduced on American railroads in the early 1900s, and were efficient as cost effective as they only required a two person crew, and were easier to maintain. Railroads also took advantage of the capability to control more than one locomotive, with a single throttle. This technology called multiple unit(MU) technology increased railroads effeiciency, and saved on labor costs. However, the cost of electric wires were too great to justify these locomotives replacing steam. Various improvements to the internal combustion systems and the introduction of fuel injection improved the design of the units, and proved to be reliable.

Although diesel locomotives were not universally accepted as feasible until after the war, decades prior there were a few example of the type built. These locomotives were usually switchers, and were used for light yard duty. Road diesels have been briefly tested by Electro Motors Corporation (EMC), a division of General Motors in the 1920s, but did not come to fruition until decades later. The first two decades of the 20th century also saw the introduction of the gasoline powered railcar, the “Doodlebug”. These railcars were frequently used on branch lines, and succeeded because of the efficiency of the gas-electric design, where the gas motor would power the traction motors, and the traction motors would turn the wheels.

Lawrence and Dave Barera

Electro Motive Corporation produced the first mass produced diesels in the mid 1930s, with the production of stream liners, which consisted of power cars and were capable of traveling at high speeds. These streamlined train sets were built by both Pullman and the Budd Company, and used the powertrain from EMC. An example of this is the Burlington Route “Zephyr” which consisted of three power cars each rated at 600 horsepower.

The popularity of these streamlined self propelled rail cars prompted EMC to enter the market producing their own locomotives. In 1937, EMC began mass production of the E series of locomotives designed for passenger service, that used the new EMD 567 prime mover, as the 567 was reliable and easy to maintain.

With EMD, the newcomer to the locomotive market, having widespread success, industry staples ALCO(American Locomotive Company) and Baldwin joined and began introducing diesel-electric locomotives into the market. ALCO and Baldwin diesel locomotives lacked the efficiency and reliability of EMD’s locomotives, and were constantly playing a game of catch up.

Even with these breakthroughs in diesel-electric technology, many railroads were not convinced and instead stuck with steam until the new diesels could prove themselves. World War II heightened this effort as the new diesels were put to the ultimate test among the dense wartime traffic, and proved to be efficient and reliable even when pushed to their limits. Afterwards, many railroads adopted diesels into their fleet, and the period of dieselization began. After the war, few steam locomotives were seen on American rails, replaced by the new diesel technology. Purchasing diesel locomotives was not as wallet-friendly as purchasing steam, however, the investment was worth utilizing less labor costs and easier and less expensive maintenance.

In the diesel market, electro motive became the frontrunner. Realizing the potential of the locomotive GE and ALCO teamed up for a shore while to go into direct competition with EMD. Fairbanks Morse also entered the diesel market, as they manufactured large opposed-piston engines that were deemed reliable and easy to maintain.

Until the mid 1950s, every railroad was replacing steam which led to many diesels being sold. However, diesel sales started to slow which led to the demise of Baldwin and Fairbanks Morse, leaving only EMD and ALCO as the premier locomotive manufacturers.

By 1960, diesels were the commonality on the rails and railroads were looking to replace older World War II era diesels with newer higher horsepower locomotives. These newer diesels produced over 3,000 horsepower, which doubled the power previously offered.

The diesel-electric locomotive became popular because it had all the functionality of electric locomotives, but without the need for costly electric wires.

The diesel locomotive has similar functionality of an electric locomotive, as it can operate using the same amount of crew members. The difference between diesel and electric locomotives is that the diesel engine carries its own power plant, which is the diesel prime mover, instead of being connected from the overhead wires.

Diesel-electric locomotives usually have two different types of electric current, AC and DC. AC current provides improved traction over DC locomotives. Two AC locomotives have the same pulling power as three DC locomotives.

Functionality of AC Current

AC current locomotives function by turning the energy from the traction alternator to DC, and then reconverting it to AC traction that is able to power the traction motors. AC motors are designed to operate close to the frequency of the current, in order to achieve this the drives have to modify the frequency in order for the speed of the motors to operate from zero to the maximum revolutions per minute(RPM)

AC TRACTION MOTOR. AC Locomotives with AC Drive. Schematic of Single Phase AC Supply Powering 3-Phase AC Motors.

Functionality of DC Current

In DC current locomotives, the prime mover creates AC current which is turned into DC current by diodes that provide power to the DC traction motors.

Many railroads were hesitant to adopt the new type of power, as many clung to their DC locomotives, as the AC variants were more expensive. However, in the recent years the prices on AC locomotives have decreased and become more affordable, with many railroads buying them by the hundreds. These types of locomotives became so popular that many roads began to convert their DC power to AC through rebuild programs.


Diesel Locomotives:





EMD GP40 Series

EMD SD70 Series

General Electric (GE)



GE C40-8/C40-8W Series

GE B40-8/B40-8W/B32-8WH

GE Dash 9 Series


Charger SC-44/SCB-40