As local factories were recovering from the war efforts, the Soviet government (then led by Joseph Stalin), ordered 20 of these locomotives.

At the time this was the world's strongest electric locomotive, with a power output of 4,320 kW (5,790 hp) being comparable to the Union Pacific Big Boy.

GE built 20 locomotives of this type, but the company was prohibited from delivering them as relations between the United States and Soviet Union deteriorated into what became known as the Cold War.

The locomotives were never delivered because the State Department banned sales of strategic goods to the Soviet Union whilst production was underway.

[3] The railroad designated its new locomotives as "class EF-4", denoting them as the line's fourth model of electric freight engine.

[4] The Milwaukee's operating employees referred to the EF-4/EP-4 units as Little Joseph Stalin's locomotives, which was eventually shortened to simply Little Joe.

The World War I-vintage General Electric motor-generator substations had difficulty supplying more than two EF-4s under heavy load, which meant that their true ability could not be demonstrated.

After being modified with increased weight, raising the maximum height of the pantographs and being provided with adequate power, the EF-4s were excellent performers and very reliable.

They were modified before delivery to remove driving controls and windows at one end to permit moving new, improved main circuit breakers into a cooler environment.

The loss of this cab was operationally inconsequential, as many Milwaukee electric locomotives were normally turned at the end of their runs in Avery, Deer Lodge or Harlowton, the road having preferred to maintain only one set of controls even on double-ended units.

The most important and final major modification was the provision of multiple unit controls for trailing diesel-electric locomotives.

One such, in 1966, resulted in the E78 being rebuilt (back east in the Milwaukee Shops) to a slightly different appearance from the other 11 units, due to the replacement of the original GE cabs with that of EMD “Bulldog Nose” cabs and the use of a pair of stainless steel side ventilation grilles intended for use on EMD F-units.

They were used on the railroad's electrified Rocky Mountain Division in Montana and Idaho to take the place of older GE boxcab electrics that had been operating there since the 1920s.

After the latter turned out to be ill-suited to the Rocky Mountain Division, they and the EP-4s were replaced by three-unit consists of EMD E-unit and/or FP7 diesels which hauled the Olympian Hiawatha end-to-end, unassisted, until its discontinuation in 1961.

By that time, they were the Milwaukee's only electric road locomotives, all the GE Freight Motors (except two which were used together in MU as the Harlowton switcher) having succumbed to old age.

The South Shore, while primarily a commuter railroad between Chicago, Illinois, and northwestern Indiana, used them in freight service.