One of the best O gauge locomotives is the K-Line MP15. The real MP15s were built in the 1970s, descended from the SW series of switcher. The originals were built between 1974 and 1984. Most used DC in their traction motors. A smaller, later batch used AC. They were very reliable machines and most are still in use. Not bad for equipment that is anywhere from 30 to over 40 years old.
The MP15 was one of the K-line’s first original locomotives. The first ones were made about 1987 in Chessie and Santa Fe liveries. Their previous offerings used recasts of Marx or KMT parts. It can be considered a scale model, though it is made for three-rail track. The MP15 is a good puller. It runs a bit fast for the scale-speed fans (weenies).
By the way: The Rock Island Railroad folded 14 years before the MP15 was introduced. K-Line was none too careful when it came to anachronisms. I have seen MP15s in Lackawanna and other railroad’s liveries that had folded long before the actual locomotive was manufactured.
K-Line made a train set called the "Greenport Scoot" based on a long Island railroad train. At one end was an Alco FA, and the other had an MP15. K-Line’s set had three passenger cars in between. I saw the real thing and it had more than three cars. The real train used the MP15 for motive power and as the cab in one direction. The FA cab was unpowered and used to control the train in the opposite direction. As I understand it, the MP15 / FA combo has not been used for a while.
And for those who insist on prototypical realism, a reminder that they have to do their own fact finding. They cannot rely on model train makers to get it right.
That MP15 switcher by K-line is a real gem, and it was priced just right. As I understand it, a company called RMT is planning to offer a remake of them. RMT has been able to buy items from China made with the old k-Line tooling. Will they be as good? You tell me. I have enough MP15s to keep my railroad in good order, so future purchases of the switcher from other makers are unlikely.