The note correcting the quick crossword clue about the world record speed for a steam locomotive (Corrections and clarifications, 5 September) raises an interesting point. According to an article by David Andrews in the August 2018 edition of the authoritative railway magazine Back Track, Mallard touched 126 mph for just one second, and therefore the substantive speed is actually 125 mph, as the LNER originally claimed. It was only much later that the momentary 126 mph was taken as the record. It is interesting to add that speeds at or in excess of 125 mph have almost certainly been achieved in the US and in Germany, but are not accepted as records because the circumstances of the performance cannot be authenticated.

Les Summers

(Railway author and contributor to Back Track), Kidlington, Oxford

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