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 14.75 x 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 39 in and was 9 ft long. Both locomotives only became useful after modifications in 1839 and 1840, where they were rebuilt with 13 x cylinders and a conventional drive. They likely received their 6 ft driving wheels at the same time. They were later converted to 2-2-2 tank locomotives, possibly when they were sent to work for the South Devon Railway Company in 1846, where they got the names Exe and Teign. The locomotives returned to the GWR in 1851. Viper operated until January 1868 and Snake November 1869. Viper was afterwards used as stationary boiler in Shrewsbury.

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