Like the Urie’s other successful 4-6-0 designs the H15 and N15 King Artur Class, for the latter see my Talking Stock #9 post here, his S15 class was built in batches both by the London and South Western Railway (LSWR) and also the Southern Railway. The first Twenty were built at Nine Elms in 1920. Their appearance is very similar the N15 class and they shared many components including the 180 lb per sq in boiler and tender designs. Being designed for heavy goods work they had 5 ft 7 in diameter drivers and cylinders of 21 in diameter.
Like the N15’s later builds under Maunsell, the newly appointed CME of the Southern Railway, also incorporated the revised front end and cab designs applied to the N15s, with the higher boiler pressure of 200 lb per sq in. Fifteen were built at Eastleigh in 1927/8 and a further ten in 1936.
The last batch were coupled to flat sided tenders, similar to the original Lord Nelson style rather than the Urie flared top style. Five of the 1927 batch, 833 to 837, were again like some N15s, fitted with six wheel tenders for use on the central section that had smaller turntables. Although primarily built for goods work they could often be seen on and keeping time on the occasional passenger turn making them versatile and as a result long lived.
I currently have a couple of S15s in my fleet that can be seen on Fisherton Sarum and these are built from DJH kits and represent the Maunsell SR built batches, one from the 1927 batch and one from the 1936 batch with the two different tenders.