Alco RSD-15 "Alligator"

The Alco RSD15, affectionately known as "Alligators" for their long, low short hood was the final six-axle RS model Alco's plant in Schenectady, New York would catalog. It was one of the most powerful models in the Road Switcher (RS) line although sales were very modest and did not top 100 units (however, it did outsell the RSD12). While the American Locomotive Company (Alco) would offer the RSD15 in either low or high short hoods most were built with the former setup, thus giving them their now classic name. For the lines which purchased Alligators most employed them where they were intended, heavy freight service.  Among the RSD models, which are not regarded as a success, the RSD15 is the most well known.  

This is surprising given the model was not Alco's top seller in the series (RSD5).  Perhaps it thanks to train enthusiasts who gave the locomotive its affectionate nickname due to its long, short hood. Because the Santa Fe ordered such a large batch several examples of this unique locomotive remain preserved today.  A few, all of AT&SF heritage, are even still operational.

Bessemer & Lake Erie RSD-15 #886 (built as Duluth, Missabe & Iron Range #55 in 1959) is seen here in Albion, Pennsylvania in August, 1971. Richard Wallin photo.

Alco actually began production on the RSD15 while its RSD12 line was also still being manufactured. The model entered the company's catalog in 1955 and remained there until 1960. It was one of just a few Road Switcher models to receive the upgraded and far more reliable 251B prime mover, which had replaced the troublesome 244 model.  The six-axle RSD15 came equipped with some serious pulling capacity at 2,400 horsepower, which was a 25% increase over the RSD12.   Additionally, thanks to its C-C truck setup (six powered axles) it offered quite impressive tractive effort with a continuous rating of 79,500 pounds. Unfortunately, since the company had experienced so many issues with the 244 engine many railroads were now leery of its products and the Alligator found few buyers. 

Those that did purchase examples included the Santa Fe, Pennsylvania, Cotton Belt, Southern Pacific, and Duluth Missabe & Iron Range. The Santa Fe's RSD15s are of particular note. The AT&SF was not necessarily a loyal Alco customer. However, the company did regularly purchase from the builder trying out most models that Alco produced. Interestingly, despite all of the manufacturer's reliability issues by the time the RSD15 entered the assembly line in 1955 Santa Fe was quite impressed with the design.   Aside from the earlier RSD7 and Fairbanks Morse's H24-66 "Train Master," the RSD15 offered the higest horsepower rating available on the market at that time. 

A trio of Lake Superior & Ishpeming RSD15s including #2404, #2401 and #2402 muscle a load of taconite ore near Marquette, Michigan on September 26, 1987. All of these "Alligators" were ex-Santa Fe units. Doug Kroll photo.

This was something the Santa Fe was after as it looked to supply ample horsepower on heavy freights crossing stiff main line grades located in western California, New Mexico, and Arizona.  As a result the railroad wound up purchasing a sizable fleet of RSD15s, 50 in all, which constituted nearly 58% of the total produced. They became famous on the AT&SF system seen throughout all three states in a range of liveries from black and silver to the "Blue Warbonnet" paint scheme. The Santa Fe was apparently pleased with their Alligators as the units remained in regular service well through the 1970s.  After their time on the AT&SF some found their way to Michigan, working heavy mineral trains on ore-hauler, Lake Superior & Ishpeming.  For more information about Alco's RSD15 model please click here.  

Production Roster Of Alco RSD15s

Owner Road Number(s) Quantity Date Built
Duluth, Missabe & Iron Range50-5561959
Pennsylvania8611-861661955
Santa Fe800-849501959-1960
Southern Pacific4816-481831959
St. Louis Southwestern (Cotton Belt)850-859101960


Taken from the head-end of another train, Santa Fe RSD-15 #9820, and what appears to be three other "Alligators," are at Ash Hill, California in March, 1972. Roger Puta photo.

As had been the case with all of Alco's RS models the RSD15 employed General Electric's model 752 traction motors and model GT586 main generator (air components, again, came from Westinghouse).  At 66 feet, 7 inches in length the RSD15 was the longest domestic model in the series. The low nose of the Alligators gave them an appearance that would actually become quite common for road switchers (although they were not the first Alco model to receive such a setup). Once again, however, Alco's designs could be easily distinguished, externally, by the notched corners on the carbody.   To read more about other Alco Road-Switcher (RS) models please visit the Diesel Locomotives section of the site, which can be reached from the top of this page.




  1. Home
  2.  ›
  3. Diesel Locomotives
  4.  ›
  5. RSD-15 "Alligators"

Header Photo: Drew Jacksich




Researching Rights-Of-Way

A popular pastime for many is studying and/or exploring abandoned rights-of-way.  Today, there are tens of thousands of miles scattered throughout the country.  Many were pulled up in the 1970's and 1980's although others were removed long before that.  If you are researching active or abandoned corridors you might want to check out the United States Geological Survey's (USGS) Historical Topographic Map Explorer.  It is an excellent resource with thousands of historic maps on file throughout the country.  Just type in a town or city and click on the timeline of maps at the bottom of the page!



Studying Diesels

You will be hard pressed at finding a better online resource regarding diesel locomotives than Craig Rutherford's TheDieselShop.us.  The website contains everything from historic (fallen flags) to contemporary (Class I's, regionals, short lines, and even some museums/tourist lines) rosters, locomotive production information, technical data, all notable models cataloged by the five major builders (American Locomotive, Electro-Motive, General Electric, Fairbanks-Morse, and Baldwin), and much more.  A highly recommended database!



Electro-Motive Database

In 1998 a gentleman by the name of Andre Kristopans put together a web page highlighting virtually every unit every out-shopped by General Motors' Electro-Motive Division.  Alas, in 2013 the site closed by thankfully Don Strack rescued the data and transferred it over to his UtahRails.net site (another fine resource).  If you are researching anything EMD related please visit this page first.  The information includes original numbers, serials, and order numbers.