The Flying Scotsman was the British steam locomotive officially recorded at 100 mph in 1934.
The locomotive was LNER No. 4472, an A3 Pacific designed by Nigel Gresley and built at Doncaster in 1923. On 30 November 1934, it hauled a light test train between London and Leeds. A dynamometer car recorded the locomotive reaching 100 mph on the return journey, making it the first steam locomotive to achieve an officially authenticated 100-mph speed.
The wording is often confused with the earlier GWR locomotive City of Truro. That engine was reported to have exceeded 100 mph in 1904, but the evidence was based on less rigorous timing and was not officially authenticated in the same way. Mallard later became the outright steam speed-record holder, reaching 126 mph in 1938, so it was faster but not first to the authenticated 100-mph milestone.
Flying Scotsman was also famous for hauling the London–Edinburgh express service of the same name. In 1928, it helped pioneer a scheduled non-stop run between King's Cross and Edinburgh, using corridor facilities and water troughs so crews and supplies could be managed without a station stop.