"Aerolite" was built in 1869 as a replacement for an engine of the same name built by Kitson's for the Great Exhibition in 1851 and which was destroyed in a collision in 1868. The engine, like its predecessor, was used to haul the Mechanical Engineer's saloon. Originally a 2-2-2WT well tank, side tanks were added 1886, and around this time it received the number 66.