 The two classes were similar but the class F was superheated.In February 1898, the Scottish locomotive builder Neilson, Reid and Company had completed an order for twelve 4-4-0 locomotives for the Great North of Scotland Railway (GNSR); these comprised GNSR class T. In October that year, William Pickersgill, the GNSR Locomotive Superintendent, requested authority to purchase a further twelve.Neilsons offered to build between ten and twenty further locomotives of the class T design.