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.
High-speed rail
In the early 1950s, the French National Railway started to receive their new powerful CC 7100 electric locomotives, and began to study and evaluate running at higher speeds. In 1954, the CC 7121 hauling a full train achieved a record during a test on standard track. The next year, two specially tuned electric locomotives, the CC 7107 and the prototype BB 9004, broke previous speed records, reaching respectively and , again on standard track. For the first time, was surpassed, allowing the idea of higher speed services to be developed and further engineering studies commenced. Especially, during the 1955 records, a dangerous hunting oscillation, the swaying of the bogies which leads to dynamic instability and potential derailment was discovered. This problem was solved by "yaw dampers" which enabled safe running at high speeds today. Research was also made about "current harnessing" at high-speed by the pantographs, that was solved 20 years later by the Zébulon TGV's prototype.