In 1958 CN again ordered another 11 1000 hp switchers from MLW but by this time MLW had adopted a new car-body for its switchers without changing the 539 engine and attendant machinery inside although the fuel tanks and air reservoirs were moved to underneath the frame. This model was designated S-12. The new car-body had a higher underframe with a step usually about one quarter of the way along the walkway on each side, a front-radiator, sand filler lids on the sides, a bulge on the left side which is an access cover to the oil filter and an insulated cab. The units were numbered 8235 to 8245 and again CN is the only railroad to have purchased this model. They were delivered in the black and yellow scheme with the maple leaf monogram.
Subsequently, they were repainted into the black and red-orange livery with the CN logo. Many units were repainted with an orange cab and reflective yellow striping on the frame. All units were retired or sold between 1982 and 1985 but 8245 is preserved and is in frequent use at the Salem and Hillsborough Railroad in Albert County, NB.