The Ea class were introduced in 1968 to replace the English Electric Eo class locomotives on the Otira to Arthur's Pass electrified section. They continued to haul mostly freight trains through the tunnel as passenger services were usually hauled by their own diesel locos and railcars ran under their own power. The Ea's were reclassified Eo as the "Ea" classification was used for wagons.
When heavier coal trains started to run from the West Coast to Christchurch in the 1980s the economics of upgrading the substation at Otira to allow more electric locomotives to be added to the head of each train was reviewed and trials began with specially modified diesel locomotives. For a time a number of withdrawn Dj class locos were based at Otira where they were used to load down these trial runs. Eventually in 1997 the electrification was dispensed with and a ventilation system allowed modified diesel locomotives to haul trains up the steep 1 in 33 grades of the 8 km Otira Tunnel.
After withdrawal, Eo 45 and 74 were transferred to Ferrymead for display and were operated in June 1998 Due to damage done to the other three locomotives on Tranz Rail property, they were also transferred to Ferrymead in November 1999 for storage.
