Mainline steam trains in Great Britain
The most famous steam locomotive operating on the British main line is the 1923 built "Flying Scotsman". After being taken into public ownership in 2004, following a decade long refit it returned to mainline service in 2016. The fastest steam locomotive ever built, the 1938 built "Mallard", was also certified for main line operation briefly in the 1980s.
4-8-4
The 242F class express passenger locomotives were designed by the "Red Nacional de los Ferrocarriles Españoles" (RENFE) in 1955 and were remarkably well-proportioned. Developed from a preceding Mountain type, they had improved steam passages and developed 30 to 40 per cent more power at medium cut-offs and high speed. Ten of these locomotives were built by "La Maquinista Terrestre y Maritima SA" in Barcelona to burn fuel oil. They had Witte type smoke deflectors and were fitted with a double KylChap (Kylälä-Chapelon) blast-pipe, a Worthington feedwater heater and a "Traitement Integral Armand" (TIA) water-softening device. To increase the comfort of the locomotive crew, the cabs had wooden floors mounted on springs, and the seats of the driver and fireman were also sprung, a very welcome improvement for long runs on poor tracks. These locomotives were painted in a green livery when turned out from the builder's works at Barcelona and were consequently nicknamed "Los Verdes" (The Greens). 
The 242F class was the fastest Spanish steam locomotive. When tested on the line from Barcelona to Tarragona across of practically level and straight line between Vilanova i la Geltrú and San Vincente, a speed exceeding was sustained twice, first with a train of 430 tons and then with a train of 480 tons. High-capacity tests took place between Madrid and Ávila when a train weighing 426 tons, including a dynamometer car, was hauled at sustained speeds of up a gradient of (1 in 286), up a gradient of (1 in 95) and up a gradient of (1 in 44.5). The gross horsepower figures recorded with the dynamometer car were 1790, 2350 and 2320 respectively, the calculated horsepower on the rail being 2600, 3400 and 3580. The latter output translates to about .