GWR Haigh Foundry locomotives

The first 19 locomotives ordered by Isambard Kingdom Brunel for the Great Western Railway included two unusual Haigh Foundry locomotives.
"Snake" and "Viper" were built at the Haigh Foundry and delivered in September 1838. They had cylinders and the driving wheels geared 2:3 to keep the cylinder stroke speed low while allowing high track speed, in line with Brunel's specifications. The boiler had a diameter of and was long. Both locomotives became only really useful after modifications in the years 1839 till 1840 they had been rebuilt with and conventional drive. Most probably they received their driving wheels at the same time. They were later converted to 2-2-2T tank locomotives, possibly when they were sent to work the South Devon Railway in 1846, where they got the names "Exe" and "Teign". The locomotives returned 1851. "Snake" operated till November 1869, "Viper" till January 1868. The boiler of "Viper" was afterwards used as stationary boiler in Shrewsbury.