World speed record for a steam locomotive is set in England, by the Mallard, which reaches a speed of 125.88 miles per hour (202.58 km/h).

A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material to heat water in the locomotive's boiler to the point where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels.

LNER Class A4 4468 Mallard is a 4-6-2 ("Pacific") steam locomotive built in 1938 for operation on the London and North Eastern Railway (LNER) at Doncaster Works to a design of Nigel Gresley. Its streamlined, wind tunnel tested design allowed it to haul long-distance express passenger services at high speeds. On 3 July 1938, Mallard broke the world speed record for steam locomotives at 126 mph (203 km/h), which still stands today.