In the mid 1980s, Northern Ireland Railways was in the process of upgrading its rolling stock. Having already purchased three new locomotives, it then proceeded to purchase replacements for its Class 70 diesel multiple units. A total of nine three car trains were constructed by British Rail Engineering Limited between 1985 and 1987 intended to supplement the existing Class 80 DMUs then in service. The trains were constructed using underframes of existing Mark 1 coaching stock, altered to and new Mark 3 bodyshells. Because of this, they bore a strong resemblance to the British Rail Class 150, British Rail Class 210, British Rail Class 317, British Rail Class 318 and British Rail Class 455, as they use Mark 3 bodyshells. These were combined with refurbished power units and traction motors from the withdrawn Class 70 units (there were only eight Class 70 units available to be salvaged, so the equipment for the ninth train came from a withdrawn Class 80 train, powercar 88 that was damaged at a collision at Hilden.)