The WAP-4 is a six-axle passenger locomotive built as a more powerful successor to the WAP-1. When trains had to be extended to 24 to 26 coaches, the 770 hp Alstom traction motors were not powerful anymore. The new locomotive got 840 hp Hitachi traction motors and a more powerful transformer. Due to the bigger weight of the electric equipment, the mechanical part of the locomotive was designed in lightweight construction. In contrast to the four-axle WAP-5 introduced only two years later, the WAP-4 only has DC traction motors and can not provide head-end power to passenger trains.

Between 1993 and 2015, 778 were built at Chittaranjan. Locomotives produced in later years partially got digital instruments in the cabs. It was the most numerous class of mainline electric passenger locomotives in India until the WAP-7 reached higher production numbers. While the WAP-4 mostly hauls heavy passenger trains, the WAP-5 is used for shorter, faster trains. Today, some WAP-4 are being used in multiple for fast freight trains.