In the early 1980s, electrification of a 255-mile section of the North Island Main Trunk (NIMT) began to increase train weights and speeds on the topographically challenging line. So the most powerful locomotives in New Zealand were built at Brush in Great Britain. They were initially plagued by many problems with the transformers.
From 2006 they were equipped with AAR couplers to be able to pull heavier trains. The withdrawals began in 2016, but this changed relatively quickly. Now, in the interest of environmental protection, further sections of the NIMT will be electrified and twelve of the remaining EF class locomotives will be modernized. The first of these went back into service in 2022.