"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 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.