In the 1970s, a heavy shunting locomotive was needed to assemble heavy passenger trains, since the existing WDS-4 were no longer up to the job. The new locomotive was given the designation WDS-6, which stood for “Wide Gauge, Diesel, Shunting, 6th Generation”. It had the same powerpack as the meter-gauge YDM-4, i.e. the six-cylinder ALCO 251-D with an output of 1,400 hp. Production started in 1975 at the Banaras Locomotive Works in Varanasi. Later, also in Parel, locomotives were assembled from components that had been manufactured in the BLW. Of the 411 WDS-6s built, many were later sold to industry or public sector undertakings. 