After "The Grouping" in 1923, the N class remained on the former SECR network, which was incorporated into the Southern Railway's Eastern section. Typical services included , Ashford and freights, and Cannon Street to Dover passenger trains. In early 1924 Nos. A815 and A825 were transferred to the former LSWR mainline between Waterloo and Guildford for trials. These proved successful, and paved the way for the allocation of most of the Woolwich batch to the Southern Railway's Western section. The type regularly replaced Dugald Drummond's ageing LSWR T9 class 4-4-0s on portions of the Atlantic Coast Express over the steeply graded mainlines west of Exeter.