New Zealand Railways classes W^AB and W^S

In 1917, two tank locomotives were built in the Addington workshops with boilers that were originally intended for class A^B Pacifics. These now had an additional trailing axle and many common parts with the Pacific, which simplified maintenance. Two almost identical variants were built in series, which were designated as W^AB for use on main lines and as W^S for use in suburban traffic. Between 1947 and 1957, some W^AB were replaced by other locomotives, after which eleven were rebuilt into class A^B tender locomotives. In the sixties the remaining W^AB were retired.