The Firefly was a class of broad gauge 2-2-2 steam locomotives used for passenger services on the Great Western Railway. The class was introduced into service between March 1840 and December 1842, and withdrawn between December 1863 and July 1879. Following the success of the Star class locomotives introduced to the Great Western Railway by Daniel Gooch, Gooch set to work to develop a new class based on North Star, but with larger boilers. The result was the Fire Fly, later followed by 61 similar locomotives designated the same class. From about 1865, the Fire Fly Class locomotives became part of the Priam Class, along with the Prince Class locomotives. The original Fire Fly is said to have covered the from Twyford to London Paddington in 37 minutes, an average speed of , which was unprecedented in 1840. Locomotives A to D Acheron 1842–1866. Built by Fenton, Murray and Jackson. The name Acheron comes from a Greek river and was later carried by a Hawthorn class locomotive. Achilles 1841–1867. Built by Nasmyth, Gaskell and Company. The name is that of a Greek mythological warrior. See Achilles. Actaeon 1841–1868. Built by Nasmyth, Gaskell and Company, the name is that of a hero from Greek mythology. See Actaeon. Arab 1841–1870. Built by G and J Rennie. An Arab is a member of an ethnic group found mainly in the Middle East and Africa. Argus 1842–1873. Built by Fenton, Murray and Jackson. Argus was the builder of the Argo, a ship in Greek mythology. Arrow 1841–1864. Built by Stothert and Slaughter. An arrow is a pointed projectile weapon. Bellona 1841–1870. Built by Nasmyth, Gaskell and Company. Bellona was a Roman goddess. Castor 1841–1874. Built by Nasmyth, Gaskell and Company. Castor was the twin of Pollux in Greek mythology. Centaur 1841–1867. Built by Nasmyth, Gaskell and Company. A centaur is a Greek mythological creature, half human and half horse. Cerebus 1841–1866. Built by Fenton, Murray and Jackson. Cerebus was a character in Greek mythology and the name was later carried by a Hawthorn class locomotive. Charon 1840–1878. Built by Fenton, Murray and Jackson. In Greek mythology, Charon was the ferryman who carried the dead in his boat. Cyclops 1840–1865. Built by Fenton, Murray and Jackson. The Cyclopes were one-eyed figures in Greek mythology. Damon 1842–1870. Built by Nasmyth, Gaskell and Company. Damon was a follower of the Greek philosopher, Pythagoras. Dart 1841–1870. Built by