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.

Type and origin
Power typeSteam
DesignerSir Nigel Gresley
BuilderLNER Doncaster Works
Serial number1870
Build date3 March 1938
 • Whyte4-6-2
 • UIC2’C1’h3
Gauge4 ft 8 12 in (1,435 mm) standard gauge
Leading Wheel dia.3 ft 2 in (0.965 m)
Driving Wheel dia.6 ft 8 in (2.032 m)
Trailing Wheel dia.3 ft 8 in (1.118 m)
Length70 ft (21.34 m)
Loco weight102.95 long tons (104.6 t; 115.3 short tons)
Total weight165 long tons (167.6 t; 184.8 short tons)
Boiler pressure250 psi (1.72 MPa)
Cylinder size18.5 in × 26 in (470 mm × 660 mm)
Loco brakeSteam
Train brakesVacuum
Performance figures
Tractive effort35,455 lbf (157.7 kN)

Further information at Wikipedia