The origins of this class date back to the 27xx class of 1901. The GWR invested heavily in six-wheeled shunting engines. These were originally fitted with saddle tanks. Then because saddle tanks would not fit easily over the boilers coming into use at the turn of the century, they were fitted with pannier tanks attached to the sides of the boiler. In 1929, after a break of 24 years, pannier tank engine production resumed with the 57xx class. 863 were built. 3650 was one of these; it incorporated an improved cab design introduced in 1933. Withdrawal from service, as diesel shunters were introduced, began in 1956.
3650 was built at Swindon in December 1939. Several pannier tank locomotives were not broken up, but were sold to outside concerns such as London Transport. In 1963, 3650 was disposed of to Stephenson Clarke Ltd, a private colliery operator at Gwaun-cae-Gurwen in South Wales, where it was painted blue with red lettering along the tanks. It was subsequently purchased by a GWS member in 1969 and moved to Hereford, where some restoration was done. However, heavy repairs were required, and in 1969 ownership was transferred to one of the Didcot volunteers, who brought it to Didcot.
3650 is now part owned by the inimitable Brian Thompson, who has gathered around him a dedicated bunch of workers that are collectively known as the "Black Cupboard Gang". Somehow they appear to have gathered more cupboards than the rest of the society owns altogether!
After some 20 years of restoration effort the boiler inspection was satisfactorily completed on 23 July 2008 and the locomotive was available for traffic. Initially the locomotive was turned out in ‘industrial’ Stephenson Clarke blue livery, but once run-in it it was painted into its original Great Western 'shirt button' livery. It became available for traffic in its new livery in April 2009.
The loco was a regular performer until late 2016 and is now undergoing overhaul. The team overhauling 3650 have compiled a photographic history of the locomotive, with an emphasis on her time at Didcot. Download 3650 Then & Now (1.6 MB .pdf file).