LB&SCR I1 Class

The LB&SCR I1 Class was a series of outside-cylinder 4-4-2 Atlantic side-tank express locomotives designed by Douglas Earle Marsh and built at Brighton Works from 1907, applying the Atlantic wheel arrangement to a tank engine configuration for the LBSCR's outer-suburban express and semi-fast services between London and the Sussex coastal towns. The 4-4-2T Atlantic tank — with four leading wheels, four coupled driving wheels, and a trailing bogie supporting the rear tanks — gave the I1 the high-speed capability of an Atlantic tender locomotive in a more compact form suited to the turn-round times of semi-fast suburban working.

Marsh designed the I1 as a high-speed tank engine for the LBSCR's outer-suburban and coastal express services: the London Bridge and Victoria to Eastbourne, Hastings, and Worthing semi-fasts that required locomotive performance beyond what the D-class 0-4-4Ts could provide, but which didn't need the full range capability of a tender locomotive. The 4-4-2T was a compact, capable solution for this traffic niche.

The I1s gave good service on LBSCR express suburban and coastal duties. They passed to the Southern Railway in 1923, where they continued on secondary express and semi-fast working. None was preserved.