The first numerically larger class of diesel locomotives in New Zealand to replace significant numbers of steam locomotives was the D^A class. It was based on the EMD G12 in the version with four driven axles. The loading gauge had been adjusted for the cape gauge routes in New Zealand. The class was initially named D^A, later the spelling was changed to DA. General Motors Diesel in Canada was awarded the contract after first delivery was promised within five months.

Production of the first 30 examples was split between GMD's plant in London, Ontario and EMD's plant in La Grange, Illinois. Together with the ten engines built by Clyde Engineering in Australia in 1957 these were referred to as Phase I. In 1961, a further twelve were delivered by GMD, forming Phase II. The largest number of units was phase III, of which 40 examples were built between 1962 and 1964 and 54 examples in 1966 and 1967.

Despite the modified loading gauge, the locomotives could not be used on many routes in the early days because they were still too big or too heavy. Only over time the cross-section of tunnels was enlarged and bridges strengthened. Another limitation were the welded bogies on Phase I locos, which did not perform well in curves and prevented the use on passenger trains. Only the locomotives from phase II onwards had new bogies with a cast frame and revised suspension, which could also be used for passenger and express trains.

DC No. 4939 and 4916 in February 2015 in Helensville

GPS 56 / https://www.flickr.com/people/91807507@N03

In 1970, six engines were equipped with slow-speed control for shunting, creating the D^AA class. From 1972 the D^A class locomotives were increasingly replaced by the new D^X class locomotives. Between 1978 and 1981, 85 Phase II and III examples were converted by Clyde Engineering to the new Class DC, bringing them to the EMD G22AR specifications. In addition to a 645 series prime mover, they received new cabs which, thanks to the dynamic brake ventilation grilles being moved to the rear, now had a low short hood for better visibility.

The unconverted locomotives were retired by 1989. Number 512 was sold to Tasmania and converted to the DAR class with a new Caterpillar D343T engine. The converted locomotives only came to the South Island after the deregulation of freight traffic. After the turn of the millennium there were problems with corrosion on the cab, leading to the possibility of the cab detaching from the frame in case of an accident, endangering the life of the driver. This meant that the locomotives could only be used behind another locomotive.

Some engines later made their way to Tasmania and Queensland and two were sold to Namibia in 2021. In July 2021, 67 of the 85 class DA vehicles had already disappeared from the roster. The last ones will probably not have a long life either, since they will be replaced by the DL class locos built by CRRC in China.