New Zealand DX Class Locomotive - Introduction

Introduction

The DX class was introduced in response to a requirement for a more powerful locomotive to handle traffic on the North Island Main Trunk (NIMT). Before their introduction the heaviest freight and passenger trains on the line required two members of the 1,060-kilowatt (1,420 hp) DA class to haul them. The DX class could haul heavier and faster trains than two DA's, even though they produced 70 kilowatts less than the combined DA's, as the single DX weighed 97.5 tonnes compared to the two DA's combined weight of 162 tonnes.

The first 15 members of the class (DX 2600 - DX 2614) were introduced in 1972. Initially, they were confined to the NIMT as their 16.25-tonne axle load was too heavy for many of the bridges on the other lines. As it was several bridges and viaducts on the NIMT had to be strengthened to take the weight of the locomotives.

There is no clear reason why the class was named the DX class. Diesel mainline locomotive classes begin with "D", followed by another letter - the mystery was why "X". Up to the DX class introduction, all classes had used letters A to J, and shunting locomotives used S. One possible explanation for the X was a reference to the 4-8-2 NZR X class steam locomotives, which ran on the central section of the NIMT between 1909 and 1957, and at the time of their introduction were the most powerful steam locomotives on NZR.

With bridges progressively strengthened throughout the North Island, and to further increase capacity on the NIMT in particular, 34 more members of the class were introduced in 1975 and 1976.