Patrick Stirling believed that locomotives with large wheels would not only be suitable for higher speeds, but would also achieve better traction. So he borrowed a 2-2-2 locomotive from the Great Eastern and used it to develop a significantly larger locomotive. By adding a two-axle leading bogie, guidance at higher speeds was improved and the increased weight was better distributed.
The driving wheels were eight feet and one inch in diameter, equivalent to 2,464 mm. The cylinders were very large at 18 by 28 inches in order to still be able to convert enough steam at the lower rotational speeds of the large wheels. In order to be able to position the boiler low despite the large cylinders and also to avoid the problems with cranked axles and high forces, the cylinders were arranged on the outside. Between 1870 and 1895 a total of 53 were manufactured, which became increasingly heavier and had a higher boiler pressure.
The Singles were also used on heavier trains on the flat line between London and York with an average speed of around 50 mph or 80 km/h. Trains with ten to 16 three-axle coaches that weighed between 150 and 240 tons in total were common on lines that rarely had a gradient of more than 1 in 200 and a maximum of 1 in 95. With lighter trains, they could reach speeds of up to 85 mph or 137 km/h.
In the “Race to the North” they ran lighter trains at average speeds of more than 60 mph or 97 km/h. Even with heavier trains, there were strict instructions not to use pilot locomotives in order to showcase the performance of the Singles. After there were two derailments in 1895 and 1896 due to the high axle load on the driving axle, the weight was reduced.
At the turn of the century, the trains became too heavy for the Singles, so pilot locomotives were now used. With the introduction of Ivatt's Atlantics in 1898, the area of operation also shifted to less important trains. Nevertheless, some received a larger domed boiler by Ivatt. After the last ones were retired by 1916, only number 1 remained as the oldest Single from 1870. It ran for the last time in 1985 and is now in the National Railway Museum in York.
