The 'A4' class of Pacific locomotives, designed by Sir Nigel Gresley for the London & North Eastern Railway in the 1930s, was arguably the most distinctive type of steam locomotive built in Britain. Their streamlined design not only reflected the art deco and modernist style of the era but was also functional, enabling them to travel efficiently at high speeds. On 3 July 1938 the most famous locomotive in the class, Mallard, broke the world speed record for a steam locomotive, travelling at 126mph. This record has never been broken. A total of 35 of these beautiful locomotives were built from 1935-38. The efficiency and speed of Gresley's design ensured they continued in top link service into the BR era, particularly London-Edinburgh but also in later years on the hilly Glasgow-Aberdeen route. In 2013, to mark the 75th anniversary of Mallard's record breaking run, all six surviving A4s were gathered together in the UK for the first time since the 1960s and fittingly Bittern set a new world speed record of 93mph for a preserved steam locomotive.This is a glorious history of the construction, design and service of the 'A4s' for over 30 years with the LNER and British Railways, and an uplifting account of the career of the six remaining A4s in preservation.