The four members of the class were built for the North Western Railway (of British India) by Vulcan Foundry in Newton-le-Willows, Lancashire, England, in 1939, and were delivered the following year.[3] Upon the partition of India in 1947, they all went to Pakistan.
The class WL of 1939 is not to be confused with the Indian locomotive class WL of 1955, the first ten members of which were also built by Vulcan Foundry.[3] According to Vulcan Foundry's publicity material, the two classes bore no resemblance to each other.[3]
