 The 421s retained the classic bulldog nose as with the other Clyde built GM and S locomotives at one end, but featured a flat-cab at the other end.In this respect, they are unique amongst bulldog nose locomotives in the world.The 421 class initially entered service on the Main South line before being transferred to Bathurst in 1970 to operate services on the Main Western line between Lithgow and Broken Hill including the new "Indian Pacific" service.