They were ordered by Evans, Walker and Gooch who were contracted to operate the locomotives for both the railways.
Daniel Gooch designed them as a development of his earlier Comet class.
They had slightly smaller wheels but larger tanks containing 1,100 gallons, a 37.5% increase.
The locomotives were bought by the SDR on 1 July 1866 after which they were operated as a combined fleet over both the SDR and CR, but they continued to be accounted to their original owner.
On 1 February 1876 the South Devon Railway was amalgamated with the Great Western Railway, the locomotives were given numbers by their new owners but continued to carry their names too.