LB&SCR J1 Class

The LB&SCR J1 Class was a series of outside-cylinder 4-6-2 Baltic side-tank express locomotives designed by Douglas Earle Marsh and introduced at Brighton Works in 1910, representing the largest and most powerful tank locomotives the London, Brighton and South Coast Railway ever built. The J1 was Marsh's response to the growing weight and speed demands of the London Victoria–Brighton express service, where the heaviest trains were exceeding what the 4-4-2T Atlantic tanks could reliably handle on schedule, and the six coupled driving wheels of the 4-6-2T arrangement provided the additional adhesion needed to start and accelerate the heavier express formations.

The 4-6-2T Baltic tank was an unusual choice for British practice: the wheel arrangement had been used in mainland European practice but was rare in Britain, and Marsh's decision to adopt it for the LBSCR's premier express tank locomotive reflected his willingness to look beyond established British convention — a quality also evident in his adoption of the GNR Ivatt Atlantic design for the H1 tender locomotive. The J1's large rear tanks and leading bogie gave the locomotive the water capacity for the sixty-mile Victoria–Brighton run and the stability for the moderate express speeds involved.

In service the J1s proved capable but not dramatically superior to the best of the I-class Atlantic tanks on the Brighton express, and they were used on a variety of LBSCR express and semi-fast duties. All passed to the Southern Railway in 1923. None was preserved.