Major customers for the S-3 included the CP, with 101; the CN, with 49; the NYC, with 43 locomotives; the B&M, with 16; and the PRR, with 13.

[1][3] ALCO and the Montreal Locomotive Works constructed approximately 300 S-3s for the North American market between 1950 and 1957.

[3] These units were essentially similar to late-built S3s, though with minor updates to the electrical gear.

In 1959, MLW built a final order of 660 horsepower switchers for the Canadian Pacific, as model S-11, numbered 6614–6623.

The internal machinery of these units was essentially the same as that of the S-10, but the car body was radically redesigned, with the radiator on the front end of the hood instead of on the sides.