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.
Steam locomotive exhaust system
Andre Chapelon made a significant improvement with his Kylchap exhaust which incorporated a "Kyala spreader" (second stage nozzle) and third stage cowl between the blastpipe (first stage nozzle) and chimney. This became popular at the end of the steam era (early-mid 20th century) and was used on the Nigel Gresley's Mallard which holds the official world speed record for steam locomotives. Other contemporary designs include the Giesl, and Lemaître exhausts which achieve the same aim by different means.