The No. 1 engine, called Locomotion, for the Stockton & Darlington Railway
Locomotion used all the improvements that George Stephenson had pioneered in the Killingworth locomotives. It used high-pressure steam from a centre-flue boiler, with a steam-blast in the chimney, to drive two vertical cylinders, enclosed within the boiler. A pair of yokes above them transmitted the power downwards, through pairs of connecting rods. It made use of a loose eccentric valve gear, and was the first locomotive to use coupling rods to link its the driving wheels together, rather than through a chain or gears. Because of the single flu, it had a poor heating surface compared to later steam locomotives.
This locomotive is historically important as being the first to run on a public railway, rather than for the innovations in its design. It hauled the first train on the Stockton and Darlington Railway on 27 September 1825.