Mallard steam locomotive. Cutaway artwork of the Class A4 steam locomotive 4468 Mallard, the fastest steam locomotive in the world. Mallard attained the record of 125.88 miles per hour (202.58 kilometres per hour) on 3rd July 1938. Mallard was built in Doncaster, UK, in 1938 and ran on the London and North Eastern Railway. It was retired in 1936 after covering nearly 2.4 million kilometres.