Probably the most iconic Pacific Express design of locomotive in Great Britain, the LNER Gresley A4, with its streamlined casing, was a classic symbol of the attitude towards speed and design in the 1930s.
The 1930s saw increased competition to the railways from road and air travel and the LNER Board knew that they had to make travel between the major cities faster, more comfortable and more reliable. High speed diesel services were starting to make an impact abroad, in May 1933, the German State Railways diesel-electric Fliegende Hamburger entered service, running for extended periods at 85mph and by 1934, in the USA, Burlington Zephyr had reached I I 2.5mph during a longer 1,015 mile journey. Nigel Gresley, the LNER's Chief Mechanical Officer, travelled on the Fliegende Hamburger and was impressed by its streamlining, although he realised it was only efficient at high speeds.
Gresley was certain that a modified A3 Pacific, with streamlining, could haul greater loads than the German or US locomotives, at the same speed or faster and a series of trials were conducted to confirm the Al's suitability. With the trials successfully completed, the LNER Board gave Gresley the go-ahead to create the "Silver Jubilee" streamlined trains, the first of the new streamlined A4s.