Immediately after the end of the First World War Lawson Billinton embarked on building more locomotives at Brighton, five of which were further Class L 4-6-4 tanks (the first two, N°327 Charles C Macrae and N°328 having been built in 1914). The first of the new batch, 329-331, appeared in 1921 with 332 and 333 following in 1922. Changes on these engines, when compared with the first two Brighton Baltics, were well tanks between the frames and very shallow side tanks of 15 ins height to overcome the initial problems of water surge experienced with the first two locomotives when their side tanks were half empty. The tanks on the new engines were, however, hidden behind tall side sheets so as to maintain a uniform appearance across the class. The leading and trailing coupled axles were fitted with large underslung laminated springs. These arrangements led to very steady locomotives which were a great improvement on the earlier ones. Initially entering traffic in grey and with just "LBSC" on the sides, a name was soon applied to the first, N°329, which was painted in umber and named Stephenson, at the request of the Stephenson Locomotive Society, in November 1921. Then N°333 entered traffic in 1922 named Remembrance as the Brighton Company's War Memorial engine, carrying a plaque inscribed "In grateful remembrance of the 532 men of the L.B.& S.C.Rly. who gave their lives for their country, 1914-1919" and painted in grey with black bands and white lining with white lettering and numbers, blocked in black, and remaining in this livery until painted green by the Southern Railway.

Then, in 1934, Maunsell commenced re-building the engines as Class N15x (an appropriate Brighton-style suffix) 4-6-0s, fitted with standard Urie LSWR tenders, starting with N°329. The fitting of smoke deflectors gave them very much a "Southern" look, quite dissimilar from the original locomotives although he used the same boiler, smokebox, firebox and etc. On being rebuilt N°327 was renamed and the locos that hadn't been named by the LBSCR were given names, 327 Charles C Macrae, becoming 2327 Trevithick, 328 becoming 2328 Hackworth, 330 becoming 2330 Cudworth (after JI Cudworth of the SECR), 331 becoming 2331 Beattie (after Joseph Beattie of the LSWR) and 332 becoming 2332 Stroudley.

The rebuilt locos weren't popular with the crews and spent their time on lesser LSWR metals, all being withdrawn by 1957, the sole survivor into that year being 32331 Beattie.