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.