GWR 1661 Class

The GWR 1661 Class was a series of inside-cylinder 0-6-0 saddle-tank shunting locomotives built for the Great Western Railway from 1876, forming part of the GWR's extensive fleet of small tank engines for goods yard shunting, station pilot, and light industrial duties. The saddle tank — in which the water tank was carried over the boiler in the shape of a saddle rather than in panniers on the boiler sides — was one of the GWR's earlier tank configurations, preceding the pannier tank that would become the GWR's distinctive standard from the late Victorian era onwards.

The 1661 Class was built at Swindon Works during the period of Joseph Armstrong's superintendency, continuing the policy of small standard goods shunting tanks that Armstrong had developed for the GWR's extensive yard and industrial requirements. The class was part of the gradual standardisation of GWR shunting motive power that Armstrong pursued, though the GWR's complex inheritance of absorbed companies and their varied locomotive fleets made full standardisation a long-term project rather than an immediate achievement.

The 1661 Class gave long service on GWR yard shunting duties, and many examples were progressively rebuilt with pannier tanks as the GWR standardised its small tank fleet on the pannier configuration. The original saddle-tank form was gradually eliminated through rebuilding rather than wholesale withdrawal, meaning that few locomotives remained in original 1661 Class condition for long. None was preserved in original form.