In 1954 American Locomotive Company unveiled a new line of diesel switching locomotives to replace the S-3 and S-4 locomotives previously offered. This new locomotive, the S-5, bore a striking resemblance to the earlier offerings with one major difference. Under the hood sat a brand new prime mover, the 251A engine. The 251 engine having just recently been developed as a replacement for the beleaguered 244 engine was first offered up in a production locomotive in the S-5.

Alco built one demonstrator, followed by an order of six locomotives for the Boston & Maine. The S-5s produced 800 horsepower, however shortly after these seven locomotives were built Alco engineers improved on the engine design. The new 251B engine now made 900 horsepower and this upgrade resulted in a new locomotive model, the S-6. Alco would go on to build 126 of these locomotives.

The S-5 and S-6 locomotives from the exterior were practically identical. These two models were improvements on the earlier S-1 through S-4 models and not total redesigns. The underframe and cab was identical to the S-4. The arrangement of machinery under the hood however was much different. The 251 engine was still arranged with the main generator closest to the cab, however the turbocharger was placed at the opposite end resulting in a much more forward located stack. The air compressor, which previously had been placed between the main generator and electrical cabinet now sat in front of the prime mover. The most obvious change was the elimination of the vertically mounted side radiators in favor of a horizontally mounted radiator with a front facing fan and louvers. There were other incremental design changes as a result of improved construction techniques. Most prominent among them was the usage of welding to replace riveting on the entire locomotive. However not all of the improvements were as well received. The new models had much more steeply inclined corner steps which made getting on and off the locomotive a little more difficult.

The original S-5 demonstrator was sold to the Island Creek Fuel & Transportation Co. as their 102. In 1972 it would be sold to Jeffboat and worked there until being scrapped on site. The six that went to the Boston & Maine were numbered 860-865. Two years after delivery their original 251A engines would be swapped out for the improved 251B engines. Later still the B&M rebuilt the 860, 861, 862 and 865 into “S-5u”s (obviously a B&M created designation) and renumbered them 1280-1283. Contemporary reports state that the horsepower of the S5us were increased to 1000 HP however that has not been verified as accurate. The 863 and 864 lived out their lives on the B&M as unmodified S-5s, save for the 251A to 251B engine swaps.

The 863 and 1281 were sold to National Iron & Metal for scrap in November, 1973. In July, 1976 the 864 was sold to George Silcott, a locomotive broker. Finally, the 1280, 1282 and 1283 went to NI&M in 1984. Silcott resold the 864 to the North Star Steel Co. mini mill in Monroe, Michigan in late 1979.

The 864 worked at North Star Steel for several years until the connecting rod bearing failed on the No.1 cylinder, which permanently took it out of service. The 864 was then acquired by the Mad River & NKP Railroad Museum and moved to Bellevue, OH, taking up residency in the museum’s coach yard. The 864 was not considered a part of the museum’s collection since it had no significance to the museum’s mission. It was acquired merely to save a rare locomotive from scrap.

In September, 2016 the Youngstown Steel Heritage Foundation approached the Mad River & NKP Railroad Museum with a proposal to acquire and preserve the 864. YSH’s mission mainly involves preserving steel industry equipment and technology primarily focusing on the Youngstown, OH area, however also owns a pair of Alco S-2s formerly used at the US Steel Ohio Works. 864, having worked as a steel mill switcher fits into YSH’s collection focus, and North Star Steel Co. did have a plant in Youngstown.

On October, 3, 2016 the donation agreement was signed by representatives of Mad River & NKP and Youngstown Steel Heritage. The agreement provides for continued storage of the 864 in Bellevue where YSH will endeavor to return the locomotive to operation. To pay homage to the fact that the locomotive is the only surviving S-5 as well as the oldest Alco product built with a 251 engine, the 864 will be painted in the dark green and yellow demonstrator scheme. The 864 is a survivor from the early days of the development of the 251 engine, an extremely successful design that has continued to be built in various forms up to the present day for a variety of uses.

We would like to see it return to New England someday.