The New Zealand EF class locomotive (originally Class 30) is a class of electric locomotives that operate on the North Island Main Trunk (NIMT) between Palmerston North and Te Rapa in New Zealand. Built by Brush Traction in Loughborough, England between 1986 and 1988 to run on the new electrified central section of the NIMT, at , they are the most powerful locomotives to operate in New Zealand. Background The NIMT is a long rail line that links New Zealand's capital Wellington and largest city Auckland, and is one of the major backbones of the country's rail network. The line was completed in 1908 and opened the following year, and included various engineering feats on the central section between Hamilton and Palmerston North, including the Raurimu Spiral and numerous viaducts – five of which are over high. Electrification of the NIMT was first proposed as early as 1918 due to coal shortages during World War I and later was proposed in the 1950s when diesel locomotives started to replace steam. The section between Wellington and Paekakariki was electrified in 1938 at 1500 V DC to prevent steam build-up in the long Tawa tunnels under the Wellington hills and to provide banking on the steep seaside section from Paekakariki up to Pukerua Bay. This electrification has since been extended further north to Paraparaumu in 1983 and again to Waikanae in 2011. Following the oil shocks of the 1970s, the National government, led by Prime Minister Robert Muldoon, launched the "Think Big" energy development projects. One of the projects involved the electrification of the central section of the NIMT between Palmerston North and Te Rapa, approved in 1980. This section was chosen for the topography of the line between these two cities, and the advantages electric locomotives had over diesel in this area. The DX class diesel-electric locomotives, then the mainstay of the NIMT and only recently introduced themselves, could handle 720-tonne freight trains on the section, but could only average when climbing the 1 in 52 gradients of the Raurimu Spiral. A more powerful locomotive, in this case, an electric locomotive, could haul a 900-tonne freight train up the same section of track at a speed of . Electric trains also had advantages during the 1970s oil shocks as New Zealand relied on imported oil to supply its diesel locomotives. Meanwhile, New Zealand's electricity supply is mainly generated from renewable hydroelectricity