Looking like something out of Thomas the Tank Engine, the 600 horsepower EMD SW-1 had the longest production run of any EMD model. EMD produced this switcher from 1939 through 1953. The SW-1 was one of the original models offered by EMD, and one of the first to use the 567 diesel engine.
Conrail inherited its fleet of 145 SW-1's from the Penn Central (136, NYC 76, PRR 60), Jersey Central (4), Reading (3), and Lehigh Valley (2). These units could be found doing what industrial switching was left, or m.u.-ed in pairs or triplets doing yard work. Due to their age and low horsepower, these units were retired by 1981.