After the Milwaukee Road had electrified 438 miles in Montana with 3,000 Volts DC, they also ordered four electric switchers from General Electric. These locomotives were built in 1916 and 1919 and were designated class ES-2. They were steeplecab locomotives with a B-B wheel arrangement and a central pantograph on the cab roof. To raise the pantograph with pressurized air when the battery was empty, an emergency trolley was provided to power the compressor.

The locomotives were only used in Montana in the Butte area, while the Milwaukee Road's other electrified section in Washington preferred steam and later diesel power for switching. With an output of 670 hp over one hour and 475 hp continuously, they later got additional weights to improve adhesion. One was scrapped in 1952 because it was surplus, but the others survived until the end of electric traction on the Milwaukee Road in 1974.