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Baldwin Loco Works official photo, Wb 297, 1898

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Operation of the Wb class.

Nine of the class of twelve Wb locomotives were initially allocated to the Wellington, Napier and New Plymouth Section of the NZR, hauling mainline trains, including the prestigious New Plymouth mail train. Two were allocated to the Westport Section, one to the Whangarei Section, where haulage of coal from inland mines to coastal ports was the predominant traffic. Allocation of Wb class locomotives was evenly split between the Westport and Whangarei sections by the First World War. More modern designs of locomotive displaced the Wb from the mainline. In addition the coal-bunker capacity had been found to be insufficient for the typical length of train-running on the steeply graded main lines. Withdrawal from service occurred during the early 1930's for all but four of the class.

The Westport Section remained isolated from the rest of the South Island network, and the six allocated Wb class had proved to be ideal for the short runs of the predominant coal traffic. A new design of boiler was fitted to four of these locomotives, extending their service life to over fifty years. A number of design modifications occurred with the fitting of new boilers, the locomotives essentially becoming an NZR locomotive on a Baldwin frame. Standard components and fittings were employed where possible, providing an opportunity for the rationalisation of spare parts.

Isolation was the key to their survival

Four Wb class survived the mass withdrawal years of the 1930's. The Westport Section was isolated from the rest of the South Island network until 1944. The only way to get replacement locomotives to and from Westport was by coastal shipping.

Isolation was not entirely removed even when connected to the rest of the network. Track and bridges were lightly built, particularly between Stillwater and Inangahua, which restricted the axleweight of locomotives able to operate through to Westport. Meantime train operation continued between the mines and the port of Westport, relatively unchanged.