Southern Railway (UK)

The Southern Railway was a British railway company established in 1923 as part of the Railways Act 1921 (also known as the Grouping Act). It was one of the "Big Four" railway companies created by the amalgamation of several smaller pre-existing railway companies.

The Southern Railway served primarily the south of England, including London commuter services and routes to ports on the English Channel, such as Dover and Southampton. It was particularly known for its extensive suburban electrification, notably using the 660 V DC third rail system, which allowed for intensive and frequent passenger services. This focus on electrification was a defining characteristic compared to the other "Big Four," which relied more heavily on steam traction.

Key constituent companies that were absorbed into the Southern Railway included:

• London and South Western Railway (L&SWR)
• London, Brighton and South Coast Railway (LB&SCR)
• South Eastern and Chatham Railway (SE&CR)

The Southern Railway invested heavily in modernizing its infrastructure and rolling stock. It introduced innovative electric multiple units and continued to expand its electrified network throughout the inter-war period and beyond. The company also operated a significant fleet of steam locomotives, which were gradually replaced by electric traction and later diesel locomotives after nationalisation.

The Southern Railway ceased to exist as an independent entity in 1948 when it was nationalized along with the other "Big Four" companies, becoming part of British Railways. The Southern Region of British Railways largely corresponded to the former Southern Railway territory. The legacy of the Southern Railway's electrification continues to shape railway services in the south of England today.