The Rimutaka Incline over the Rimutaka Ranges posed a severe time delay to any service operating between Wellington and the Wairarapa region. At one end of the Incline, a train had to have its engine replaced by multiple members of the H class, as the H class locomotives were specially designed to work the steep and difficult Incline. Once they hauled the train the length of the Incline, they were then replaced by a single ordinary engine. The procedure to attach and remove the H class locomotives, as well as the actual trip along the Incline, was very slow.