Next loco is WAM 4. It was the first locomotive completely designed and developed in India by Indians. t took the RDSO and CLW only 10 years after the first WAM1 rolled out to come out with the completely “made in India” WAM4.Though indigenous, they were ‘inspired’ by the WAM1 and WAG1 with added Silicon Diode rectifiers and rheostatic braking. However, the masterstroke was adapting those ultra-successful ALCO Trimount bogies of the WDM2 for the WAM4. With the huge success of the ALCO, IR had finally figured out that Co-Co (two bogies with three axles each, all axles powered by individual traction motors) was the most favorable wheel arrangement configuration for India as it provided more stability and pulling power for typical heavy loaded Indian trains at the cost of some speed. All these factors culminated in the WAM4s celebrated versatility, easy maintenance and ruggedness leading to the huge success of the class. Sheds and workshops across the country created their own modifications to the WAM4 resulting in a huge number of variants and subtypes. Unlike the diesels, subtype notations here do not mean power but modifications on the locomotive. This locomotive had a top speed of 120 kmph and 500 locomotives were produced in this period of 1970 to 1983.