From 1846, John Gray had twelve 2-2-2 express locomotives built for the LB&SCR, which are considered the forerunners of the Jenny Lind type. Although they had outside and inside frames, the driving axle with the six-foot wheels was only mounted on the inside frame. They already had a firebox with a round, raised ceiling, on which sat a second steam dome. They were said to be able to easily reach a speed of 40 mph with the train weights that were common at the time. Under Craven, all were rebuilt to a different wheel arrangement in order to collect experiences with the characteristics of the different types and their suitability for different tasks.
During the first rebuild in 1853, four were rebuilt into 2-4-0 freight locomotives. The diameter of the driving wheels was now four feet and nine inches. Later, three of them were rebuilt into 0-6-0T tank locomotives by exchanging the leading axle for another driving axle with the same wheel diameter.
Between 1853 and 1855, six others were rebuilt into passenger locomotives, which, like the freight locomotives, had 2-4-0 wheel arrangement. However, these had a driving wheel diameter of five and a half feet. The fact that none of these were rebuilt again and remained in use until the 1870s suggests that they were considered successful in this form.
The other two locomotives were rebuilt to the Crampton design, which was a special design with a crankshaft. At the front end, the two carrying axles sat a short distance apart in the frame and behind the firebox was the driving axle, the wheels of which were still six feet in diameter but clad in a wooden wheel disc with no visible spokes. The inside cylinders worked on a crankshaft and drove external connecting rods. Both locomotives only ran in this form for about two years and were rebuilt into 2-4-0 freight locomotives in 1855. One of these two was rebuilt into a tank locomotive with the same wheel arrangement in 1858 and remained in service until 1875.
