The streamlined A4 class was designed by Sir Nigel Gresley to power high-speed trains. Its high power in combination with its aerodynamic body allowed the class to easily reach speeds of over 100 mph (160 kph) although in everyday service it rarely went that fast. No regular steam-hauled rail service in the UK reached even 90 mph let alone 100 mph. The Mallard covered almost 1.5 million miles (2.4 million km) during its working life.
It was retired in 1963 but restored to working order in the 1980s though it was not in operational use apart from hauling some specials between York & Scarborough in 1986 and a couple of runs between York and Harrogate/Leeds in 1987. The Mallard is now part of the National Collection in the Great Hall at the National Railway Museum in York. On the weekend of 5th July 2008 the Mallard was taken outside for the first time in years and displayed beside the other three A4s that are resident in the UK which re-united them for the first time since their preservation. It was hauled to Locomotion on 23rd June 2010 where it was a static exhibit until it was hauled back to York on 19th July 2011 and put back on display in its original location in the Great Hall which is well worth a visit as it contains a fascinating collection of railway legends from history-makers to record-breakers. This former engine shed is home to over 300 years of railway history including some of the biggest locomotives in the National Collection.
BBC News: Magnificent Mallard – World’s fastest steam locomotive!