In the late 1950s, the Milwaukee Road's electrification was starting to slowly unravel as their electric fleet started to collapse from old age. Coincidentally, the industrial base of the northeast started to unravel in the 1950s and the PV&T found itself with too many locomotives for its operational needs. The electrification departments of the PV&T and Milwaukee Road had many contacts (being the only two mainline freight 3000VDC electrifications in North America) and an agreement was made to loan the Milwaukee Road a pair of surplus class B3s so that they could evaluate them (and give the PV&T a small revenue source instead of simply scrapping the unused engines.) The class B3's were successful in the west, and over the course of 4 years 14 other class B3s moved west to join them.
Unfortunately, the Milwaukee Road still scrapped their electrification in 1974, so the 16 B3's returned to the East Coast, along with 9 hastily purchased Little Joes, and steeplecabs E81 and E82.