The class is an A1A-A1A version of the Electro-Motive Diesel (EMD) G12 model, with the design altered slightly to run on New Zealand's 3 ft 6 in (1,067 mm) rail system, and fit the small loading gauge.

Like most nations, New Zealand's dominant form of railway traction was steam, with electrification being used in Wellington, the Christchurch - Lyttleton Line and through the Otira Tunnel.

The General Manager of the New Zealand Railways (NZR), Frank Aickin, was an advocate for electrifying the entire North Island Main Trunk (NIMT) to alleviate the shortage of coal and the cost of importing diesel fuel; though he also recognised that steam or diesel traction would be required on other lines.

The order was approved by Cabinet on 26 June 1956 on Clyde Engineering for ten DA class locomotives, to cost £NZ674,560.

This followed a visit to Clyde in Sydney on 13 June 1956 by the Minister of Railways John McAlpine and the NZR General Manager Alan Gandell.

To facilitate their fast delivery a greater loading gauge was accepted meaning that initially they could only operate on the NIMT from Auckland to Paekakariki, and the Rotorua, Kinleith and Tokoroa branches.

[18] The first (1955) locomotives had fabricated bogies welded from steel pressings and because of the roll on curves were restricted to goods service.

Later batches (from DA 1440) had Dofasco cast steel bogies with an improved spring layout and were suitable for express working.

The operational practice remained the same as it had in the steam age, with an exchange with ED and EW class electric locomotives taking place at Paekakariki.

The success of the DA class in its reliability and performance meant that it was the major factor allowing the withdrawal of North Island steam locomotives by 1967.

The prestigious Silver Star overnight sleeper train was initially hauled by a pair of DA class locomotives when it was introduced in 1971.

While a single DX produced 70 kW less than a pair of DA class locomotives, it weighed 97.5 tonnes compared to the combined weight of two DA class at 162 tonnes, which combined with more powered axles gave better traction and higher power to weight ratio.

[14] The combination of the deregulation of land transport and the decline in rail freight volumes, reduced inter-regional passenger numbers, and the electrification of the NIMT saw them become surplus to requirements.

In 1979 the computerised Traffic Monitoring System (TMS) was introduced, with the remaining members of the class renumbered in sequence and the classification capitalised.

In 1970, locomotives DA 1400-04 and 1406 were withdrawn from mainline duties and reassigned as heavy shunters to work in the new Te Rapa hump yard.

[24] These locomotives were identifiable by their yellow hood stripes, which were treated to denote them as being used in special service apart from the DA class.

In 1988, the locomotive was purchased by enthusiast Tony Bachelor, who moved it around various homes in the Auckland area as part of his Pacific Rail Trust.

Two locomotives - DAs 1533 and 1470 were both rebuilt from heavily damaged conditions sustained in accidents running light engine.

DA 1470 derailed on the steep Pukerua Bay section in 1978, returning to Wellington due to speeding on a curve, and nearly ended up on State Highway 1 below the line; both of the crew were killed.

After a long period of inactivity, the locomotive, which had been partway through a rebuild to make it more suitable for Tasmanian conditions, was sold for scrap by TasRail in mid-2011.

This locomotive had been rebuilt in the late 1970s with a new Caterpillar D343T diesel engine and torque converter to make it more effective as a heavy shunter, but due to increases in traffic, was no longer able to keep up.

[nb 3] At the same time, NZR was withdrawing the last DA class locomotives, and the decision was made to offer DA512 as a new heavy shunter.

DA512 was sold to Tranz Rail Limited who immediately moved it to Hutt Workshops for further alterations to make it more suitable as a heavy shunting locomotive.

Renumbered as DAR 517, the locomotive was released from Hutt in 1999 and allocated to the Kiwi Dairies milk factory at Whareroa, near Hāwera.

It was repainted in the Toll Rail "Corn Cob" colours in 2005, but was withdrawn from service in September 2008 for an overhaul and was placed in storage at Hutt Workshops.