N°515 had the distinction of twice being converted to oil firing, once in 1921 and once in 1926. On both occasions, though, she was restired to coal firing.

Like their contemporaries the N15s further batches were built by the Southern Railway under the auspices of Richard Maunsell, and these builds 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 first Eastleigh batch included engines for use on the Eastern and Central sections and some were fitted with six wheeled tenders for use where there were small turntables. Like the N15s over time tenders were swapped around not only within the class but also with N15s, the Schools class (which received their six wheeled tenders) and with the Lord Nelson class. Smoke deflectors were fitted to all of the class during the mid 1930s.

During 1942 four engines (496-9) were on loan to the GWR and whilst on that railway had a GWR shed code stencilled on the angle iron.

The modified design provided an excellent goods engine and they were best known for working heavy night express goods trains between Exeter and Nine Elms and Southampton and Nine Elms. They were also adaptable and were capable of putting up a creditable performance when pressed into passenger service during peak holiday periods. They outlived the King Arthur class, first withdrawals were in 1962 and the final members of the class were still in regular service in 1965. The last withdrawal, 30837, was in 1966. This had officially been withdrawn in 1965 but was retained to work an enthusiasts' special. Two Urie and five Maunsell S15s have survived into preservation.