The Class A4 is a class of streamlined 4-6-2 steam locomotive designed by Nigel Gresley for the LNER 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; they themselves proving to be worthy successors to the A4s.

Several A4s saw out their remaining days until 1966 in Scotland, particularly on the Aberdeen to Glasgow express trains, for which they were used to improve the timing from 3.5 to 3 hours. Six have been preserved.