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.
Milwaukee Road class A
They hauled the fastest scheduled steam-powered trains in the world. Running at 100 mph or greater was required to keep these schedules; the class A locomotives were designed to cruise at over and be able to achieve . A run with a dynamometer car behind the locomotive was made on May 15, 1935 by locomotive No. 2 between Milwaukee and New Lisbon, Wisconsin. Over a stretch the speed of was recorded. This was the fastest authenticated speed reached by a steam locomotive at the time, making No. 2 the rail speed record holder for steam and the first steam locomotive to top . There are reports, without evidence or accurate records, that these locomotives could exceed . Such speeds would have placed the class A in contention with the LNER Class A4 and German BR 05 for the crown of fastest steam locomotive until that time, but no records have been unearthed. The successor Milwaukee Road class F7 was even more powerful, with a claimed top speed of .