GWR Sun Class

The GWR Sun Class was a series of early broad-gauge 2-2-2 express locomotives introduced in 1839 as part of Daniel Gooch's first wave of purpose-designed GWR engines, roughly contemporary with the Mercury Class and immediately preceding the definitive Firefly Class of 1840. The Sun Class formed part of the transitional group of Gooch designs that bridged the gap between the heterogeneous opening fleet (including North Star) and the standardised Firefly Class that would transform GWR express performance.

Named in the celestial tradition that Gooch applied to several of his early GWR locomotive classes, the Sun Class used the 2-2-2 single-driver broad-gauge layout with driving wheels approaching the 7 ft diameter that would be standard on the Firefly. Gooch was in this period learning the operational requirements of the GWR's main line and refining his designs accordingly; the Sun Class represents one stage in that learning process, a reasonably capable early express type that was quickly superseded by the improved Firefly design.

The Sun Class worked early GWR broad-gauge express services in 1839–40 before the Firefly's arrival and gave competent if unspectacular service. None was preserved.