Mallard

Mallard is the holder of the world speed record for steam locomotives at 126 mph (203 km/h). The record was achieved on 3 July 1938 on the slight downward grade of Stoke Bank south of Grantham on the East Coast Main Line, and the highest speed was recorded at milepost 90¼, between Little Bytham and Essendine. It broke the 1936 German (DRG Class 05) 002’s record of 124.5 mph (200.4 km/h). The record attempt was carried out during the trials of a new quick-acting brake (the Westinghouse “QSA” brake).

Mallard was a very good vehicle for such an endeavour. The A4 class was designed for sustained 100+ mph (160+ km/h) running, and Mallard was one of a few of the class that were built with a double chimney and double Kylchap blastpipe, which made for improved draughting and better exhaust flow at speed. (The remainder of the class were retro-fitted in the late 1950s.) The A4’s three-cylinder design made for stability at speed, and the large 6 ft 8 in (2.03 m) driving wheels meant that the maximum revolutions per minute (529.4/min at 126 mph) was within the capabilities of the technology of the day. Mallard was just four months old, meaning that it was sufficiently broken-in to run freely, but not overly worn. Selected to crew the locomotive on its record-breaking attempt were driver Joseph Duddington (a man renowned within the LNER for taking calculated risks) and fireman Thomas Bray.

Further information at Wikipedia