The Southern Railway took a key role in expanding the 660 V DC third rail electrified network begun by the London & South Western Railway. As a result of this, and its smaller operating area, its steam locomotive stock was the smallest of the 'Big Four' companies.
For an explanation of numbering and classification, see British Rail locomotive and multiple unit numbering and classification.
British Railways completed construction of the 'West Country' and 'Merchant Navy' locomotive designs but did not build any further orders. It abandoned the 'Leader' class experiments, and Bulleid left the UK to carry forward his unusual locomotive designs in Ireland.
Withdrawal of ex-SR locomotives happened mainly towards the end of steam on the Southern Region (in 1967), the pre-Grouping designs having gone before then as electrification spread across the region.
With the heavy emphasis on electrification for the London suburban area and the Brighton mainline, there was little need for new steam locomotive designs. The main steam tasks were boat trains (Dover, Folkestone and Newhaven), West of England, Kent services and freight. When designing steam locomotives, the designers had some interesting constraints that dictated where the locomotive could be used. Due to the hangover from SE&CR days, most of the lines in Kent were of fairly light construction and would not take the weight of a modern express locomotive until well into the 1930s. Hence the extensive rebuilding (and new construction) of 4-4-0 designs at a time when other lines were busily building Pacifics or heavy 4-6-0s.
The ex-SER lines also had the problem of the narrow Mountfield and Wadhurst tunnels on the Hastings line, requiring locomotive and rolling stock rather narrower than permitted elsewhere. This problem persisted into British Railways days until eventually the tunnels were single tracked, giving clearance for normal stock.
Services for west of Southampton and Salisbury had a different set of problems as neither the Southern Railway nor its constituents installed water troughs, thus leading to large tenders with greater water capacity than those fitted to similar locomotives on other railways.
New designs were:
Maunsell also rebuilt, modified or continued the new construction of earlier classes
Bulleid was also responsible for the mechanical part of the three electric locomotives (CC1–CC3, later British Railways Class 70) built at Ashford Works in 1941 (CC1) and 1948 (CC2, CC3). The electrical part was the responsibility of the Southern Railway's Chief Electrical Engineer, Alfred Raworth. Bulleid also designed a 500 hp 0-6-0 diesel mechanical shunter powered by a Davey Paxman power unit. This was built at Ashford Works, though was not introduced until 1950, when it emerged as BR No. 11001.
No SER locomotives built – stock administered by the London and Croydon, South Eastern, and London and Brighton Joint Locomotive Committee.
Stirling, like his brother Patrick, built engines with domeless boilers. Many, however, were rebuilt with domes in later years.
Initially, LC&DR engines were given names, they only received numbers after 1874.
On the merger with the South Eastern in 1898, engine numbers were increased by 459, this being the highest number in use on that line.
Before 1899, both the South Eastern Railway and the London, Chatham and Dover Railway had some Crampton locomotives built by Robert Stephenson and Company. The SER also had some Cramptons built by Tulk and Ley.
Many of these engines were later renumbered, frequently into the "duplicate" series above 600.
Following the grouping, LB&SCR locomotive numbers were prefixed with "B", but in 1931 the prefix was removed and 2000 added to the number.