An “oil electric” was a Diesel, but World War I was too fresh in people’s minds to use that term in 1926. This particular locomotive was built by three companies: Ingersoll Rand built the Diesel, General Electric the generator and motors, and Alco the rest of the locomotive.
These three companies built a demonstrator model in July, 1925, and the Long Island Railroad was one of the first companies to buy one in January, 1926. The brochure says that it was used by the Long Island in switching service 24 hours a day, seven days a week, from February 15 to May 2.
The brochure has an artist’s conception of a single locomotive like this one, but a bit more streamlined, pulling the full-sized heavyweight passenger train, but that was never going to happen. This locomotive had just 600 horsepower, and most railroads ended up needing at least 3,600 horsepower (two E7 locomotives) to pull either heavyweight or lightweight streamlined trains.
I copied this brochure from the Great Northern archives at the Minnesota History Center, so the image is not as sharp as I would like. Apparently, the brochure persuaded Great Northern to buy a locomotive like this one, as it took delivery of one in September, 1926.