The London, Brighton and South Coast Railway E6 Class was a class of 0-6-2T side tank steam locomotive designed by Robert Billinton. They were introduced in 1904 and were a development of the E5 class with smaller driving wheels intended for heavy short and medium-distance freight trains.
The E3 class radial tanks were useful on all but the heaviest freight trains in congested the London area, which required rapid acceleration from signals in order to avoid holding up other traffic. Robert Billinton therefore produced a version of his successful E5 passenger tank class with smaller 4 ft 6 in (1.372 m) driving wheels for this purpose. Twelve locomotives were built by Brighton Works between December 1904 and December 1905. The last two locomotives were originally intended to be built as 0-8-0s for heavy shunting purposes but Billinton died in November 1904 before any were built and the order was subsequently changed by his successor D. E. Marsh.
The E6s were successful goods locomotives, but in 1911 two examples were rebuilt with the larger C3 class boiler and a C2X class smokebox and were re-classified E6X. These two locomotives proved to be very powerful, but used significantly more fuel and no more examples were rebuilt.
The London, Brighton and South Coast Railway (LB&SCR; known also as "the Brighton line", "the Brighton Railway" or the Brighton) was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey. It was bounded on its western side by the London and South Western Railway (L&SWR), which provided an alternative route to Portsmouth. On its eastern side the LB&SCR was bounded by the South Eastern Railway (SER) – later one component of the South Eastern and Chatham Railway (SE&CR) – which provided an alternative route to Bexhill, St Leonards-on-Sea, and Hastings. The LB&SCR had the most direct routes from London to the south coast seaside resorts of Brighton, Eastbourne, Worthing, Littlehampton and Bognor Regis, and to the ports of Newhaven and Shoreham-by-Sea. It served the inland towns/cities of Chichester, Horsham, East Grinstead and Lewes, and jointly served Croydon, Tunbridge Wells, Dorking and Guildford. At the London end was a complicated suburban and outer-suburban network of lines emanating from London Bridge and Victoria, and shared interests in two cross-London lines.