LB&SCR I5 Class

The LB&SCR I5 Class was a series of outside-cylinder 4-4-2 Atlantic side-tank locomotives designed by Douglas Earle Marsh and introduced in 1909 alongside the I4, representing a slightly different variant specification within the LBSCR's ongoing Atlantic tank programme. The I5 differed from the I4 in detail boiler or cylinder dimensions, and the two classes were built in the same year to meet the LBSCR's demand for additional high-speed tank engine capacity on the Sussex coastal and outer-suburban services.

The proliferation of I-class variants in 1909 — I4, I5, and I6 all introduced in the same year — suggests that Marsh was simultaneously building and evaluating slightly different specifications to identify the optimum Atlantic tank configuration for the LBSCR's operating conditions. This systematic variation approach was characteristic of the period before established standards in superheater and valve gear design had fully settled the question of the best specification for any given duty.

The I5s passed to the Southern Railway in 1923. None was preserved.