In 1942, the East Indian Railway initially had four tank locomotives with a 2-6-2T wheel arrangement built for suburban services in Calcutta. These were supplied by the Vulcan Foundry in England and designated Class WV. A good compromise between speed and traction was found with a driving wheel diameter of 67 inches. They had a Belpaire firebox and compensating levers on the three coupled axles. However, it quickly turned out that the water and coal reserves were too small.

As a result, ten more locomotives were built in 1942, which had a bogie instead of the trailing axle, which meant that significantly larger supplies could be accommodated. With that, the WM class was born and the four WVs were also rebuilt into the WM. Only after the restructuring of the Indian Railways, each 30 more locomotives from Vulcan and Robert Stephenson and Hawthorns were built.