LNER Class A4
The Class A4 is a class of streamlined 4-6-2 steam locomotive designed by Nigel Gresley for the London and North Eastern Railway in 1935. Their streamlined design gave them high-speed capability as well as making them instantly recognisable, and one of the class, 4468 "Mallard", holds the world record as the fastest steam locomotive. Thirty-five of the class were built to haul express passenger trains on the East Coast Main Line route from London Kings Cross via York to Newcastle, and later via Newcastle to Edinburgh, Scotland. They remained in service on the East Coast Main Line until the early 1960s when they were replaced by Deltic diesel locomotives. Several A4s saw out their remaining days until 1966 in Scotland, particularly on the Aberdeen - Glasgow express trains, for which they were used to improve the timing from 3.5 to 3 hours.
Race to the North
On the East Coast route, GNR locomotives ran on what was undoubtedly the fastest line in the world but the ""Flying Scotsman"" service was not their fastest train – compared with, say, on routes with more competition. A wide variety of locomotives was in use – the Patrick Stirling 4-2-2 "8-foot" singles, complemented with his 2-2-2 "7-foot 6" singles, were outstanding for speed and reliability, being capable of on flat terrain. The latest express NER engines were Tennant 2-4-0s and the T.W. Worsdell–von Borries compound Worsdell 'F' 4-4-0s which were powerful, although not so fast.
Having compound engines required the development of sufficiently strong steel connecting rods for fast running and the 4-4-0s developed from 2-4-0s when it was found that a front bogie gave greater high speed stability. The East Coast route had no severe gradients and was slightly shorter than the west.