Between 1859 and 1860, the LCDR board considered the need for new locomotives to operate lines then under construction.
After discussion with William Martley, the quantities needed for the two passenger types were revised to five and 24 respectively.
Tenders were sought, and these were considered in July 1860, when orders were placed with several firms for what were to become the Echo, Tiger and Acis classes.
[2] As with the Echo and Tiger classes, the locomotives were equipped with the Cudworth coal-burning firebox.
[5] In November 1875, William Kirtley (who had replaced Martley following the latter's death in 1874) allotted the class letter H.[6] The locomotives were then given the numbers 113–126.