BR Southern Region

'BR Southern Region' is used in this encyclopedia for traction and rolling stock projects led by the British Railways Southern Region engineering organisation, which after 1948 inherited one of the most distinctive railway engineering cultures in Britain — the Southern Railway's third-rail DC electrification tradition and the Bulleid steam legacy that together gave the SR its unique character among British railways.

The Southern Region's engineering identity was defined above all by its extensive commitment to third-rail 750 V DC electric traction, a system the SR had inherited from the LSWR and developed aggressively through the 1930s and 1940s until it covered the majority of the SR's passenger routes. After nationalisation the Southern Region continued extending this electrification, reaching Kent via the Kent Coast scheme in 1959 and completing the Bournemouth electrification in 1967, progressively eliminating steam from the SR's main-line services decades before other BR regions.

In locomotive terms the Southern Region's most notable post-war contributions were the Class 71 Bo-Bo DC electric locomotive for heavy express and freight workings on the electrified network, and the Class 73 electro-diesel — an ingenious design capable of drawing power from the third rail or operating on its own diesel engine, giving SR locomotives the ability to work over both electrified and non-electrified routes without locomotive changes. The Region's engineering traditions continued until the SR was absorbed into the Network SouthEast sector in 1986 as part of BR's sectorisation.