Diesel locomotives, technically known as diesel-electrics, came into widespread use here in the United States with the development of the Electro-Motive Corporation’s (EMC, later to become the General Motors' Electro-Motive Division, or EMD) EA/EB design, first tested on the Baltimore & Ohio Railroad (B&O) in the late 1930s. The diesel-electric locomotive would also become a major milestone in technological development for North American railroads as it symbolized the end of the only motive power type (aside from electrics) to be used in the industry up until that time, the steam locomotive.
The mechanics of diesel locomotives are rather straightforward, although it is commonly mistaken that the diesel engine itself propels the locomotive, which is not the case. While the diesel engine is the prime mover the energy it creates drives an electrical generator, which in turn drives the traction motors found within the locomotive’s trucks that actually turns the wheels (or the mounts which sit over the axles) and propels unit forward. The diesel engine itself has no connection to the actual motion of the wheels and in essence the locomotive is an electric locomotive which carries its own power source on board.
Diesel-electric locomotives have been around in one shape or form since 1918 when the American Locomotive Company (Alco) joined with General Electric and Ingersoll-Rand to produce a motor car design for the Jay Street Connecting Railroad, #4. Designated as model GM-50 it was essentially a diesel powered motor car, somewhat similar to an interurban car, and built in conjunction with Alco and Ingersoll-Rand. Later, in 1924 the three companies built a 300 hp, 60-ton boxcab design that would be purchased by the Central Railroad of New Jersey, followed by the Baltimore & Ohio Railroad.
The B&O also has the distinction of being the first railroad in the country to purchase a diesel-electric passenger locomotive in 1935 from EMC (B&O #50). While these early designs were somewhat successful and new diesel switch engines were becoming quite popular from makers such as Alco, it would not be until the development of EMD’s legendary E and F models (which followed the EA/EB design they were nicknamed "covered-wagons") to pull heavy passenger and freight consists did the diesel-electric locomotive really come of age and overtake the steam locomotive as the dominant means of moving freight across America’s rails.
It would take the diesel-electric locomotive nearly fifty years to equal the horsepower output of the steam locomotive during its technological height. However, diesels offered an advantage that far surpassed steamers and it was the deciding factor in them becoming the prime choice of motive power, efficiency. Diesels required far less maintenance in terms of overhauls (scheduled time in the shops for routine maintenance) and refueling (no longer were there frequent stops requiring water and coal/oil), which allowed them to be spending much more time moving freight and paying the bills.
Below you can find each manufacturer and a number of their most popular first and second-generation diesel locomotive models. Simply click on their link to learn more about them.
American Locomotive Company (Alco)
Baldwin-Lima Locomotive Works (BLW)
General Electric (GE)
General Motors’ Electro-Motive Division (EMD)/Electro-Motive Diesel
Notable Prime Movers
Diesel locomotives have come a long way from the early designs by EMC and Alco-GE-IR, with comfort cabs and electronic equipment the norm on new units now being built by Electro-Motive Diesel (now an independent company having been spun-off by EMD in 2005) and GE. However, when the diesel was first coming of age there were still several builders, many of whom were legendary steam locomotive manufacturers (such as Baldwin, Lima, and Alco) that began switching to diesel-electric development when the writing on the wall became apparent that steam's days were numbered. Finally, if you are interested in full fallen flag diesel locomotive rosters I have moved this to each individual railroad's page. You may find them here.
While a few of the steam locomotive manufacturers were marginally successful, most notably Alco, all of these once mighty companies would be gone before 1970 (mostly the result of management never able to truly see that steam was in its twilight and diesels were the future). While many of these companies no longer manufacture locomotives, their legacies will forever live on and many of both their steam and diesel locomotive models still survive, some even continuing to haul freight. Also, while diesel locomotives may have replaced the mighty steam locomotives, nothing can quite compare to seeing steam power at work!