They were ordered by the South Devon Railway which was contracted to operate the locomotives for both the railways. They were designed by Daniel Gooch a development of his earlier Comet class, and built by the Avonside Engine Company.
The locomotives of the three railways were operated as a combined fleet by the South Devon Railway but each was accounted to the railway that ordered it. 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.
On a foggy Christmas Day in 1883, Gorgon was put on the front of a train at Newton Abbot railway station to assist it over the heavy gradients to the west. After leaving the station the driver realised that he did not have the train behind him. The driver slowed down, only for the remainder of the train to emerge from the fog and collide with his locomotive. Gorgon was named after a Greek mythological monster, the Gorgon.
Sedley (1866 – 1885) GWR no. 2124
Sedley was the first broad gauge locomotive to take a passenger train through to Penzance when the West Cornwall Railway was converted to mixed gauge. The derivation of this name is uncertain.
Pluto is believed to have been one of the two locomotives on the last passenger train from Penzance on 20 May 1892 before the broad gauge was abandoned. Named after a Roman mythological character, Pluto.
Waters, Laurence (1999). The Great Western Broad Gauge. Hersham: Ian Allan. ISBN0-7110-2634-3.
Beck, Keith; Copsey, John (1990). The Great Western in South Devon. Didcot: Wild Swan Publications. ISBN0-906867-90-8.
Reed, P.J.T. (February 1953). White, D.E., ed. The Locomotives of the Great Western Railway, Part 2: Broad Gauge. Kenilworth: The Railway Correspondence and Travel Society. ISBN0-901115-32-0. OCLC650490992.
Gregory, R H (1982). The South Devon Railway. Salisbury: The Oakwood Press. ISBN0-85361-286-2.