After the Coast Division was electrified via the Cascades, the Milwaukee Road procured very large passenger locomotives for the increasingly heavy trains. Due to the allocation of orders between manufacturers made by the US Railroad Administration, a further ten EP-3 from Baldwin-Westinghouse were built in parallel to the five EP-2 from General Electric. Although the EP-3 was heavier, it appeared more graceful in general.

The locomotive body was not split here, which made greater demands on the layout of the chassis. In principle, the locomotives each consisted of two chassis groups, each of which resembled a Pacific steam locomotive and were coupled to one another. Each axle was driven by a double motor, which was mounted in the frame and was therefore not part of the unsprung mass. Power was transmitted via a quill drive, which gave the locomotives the nickname “Quills”. Above the coupling between the chassis parts was the oil-fired oven for the train heating,

Due to the relatively rigid overall design and the lack of flexibility of the axles, the great wear and tear on the wheel flanges soon became apparent during operation, and there were also derailments. In retrospect, the weight-saving design of the locomotives did not prove to be advantageous either, so that the frames broke. Splitting the locomotive body of one of the locomotives into two parts did not help and even several modifications to the chassis and other parts of the locomotives could not eliminate all problems.

After the Second World War, the EP-4 „Little Joe” took over the duties of the EP-3. While other electric locomotives, badly worn out during the war, had been rebuilt, this was not considered useful for the EP-3. Thus, the seven remaining vehicles were all scrapped between 1952 and 1957.