The LB&SCR D1 class were powerful 0-4-2 suburban passenger tank locomotives, designed by William Stroudley of the London Brighton and South Coast Railway in 1873. They were originally known as "D-tanks" but later reclassified as class D1. Members of this very successful class survived in service until 1951. Background The D1 class were Stroudley's second tank engine class, intended for heavier tasks than could be undertaken by his A1 class "Terriers" which had been introduced in 1872. They had larger 5 ft 6 in driving wheels and a boiler pressure. Between November 1873 and March 1887, 125 locomotives of the class were built, 90 of which at Brighton railway works and the remainder by Neilson and Company After 1883, new locomotives were given boilers with pressure, and in 1892 following Stroudley's death, the boiler pressure for replacement boilers was raised to . Pre-grouping The class was the mainstay of the LB&SCR outer suburban services for twenty years, until gradually replaced by R. J. Billinton's D3 class 0-4-4 tank engines in the mid-1890s. Thereafter they were used on a variety of secondary passenger, and occasionally freight services throughout the railway. The first locomotive was withdrawn in December 1903, but many of the locomotives were still in good condition and popular with the engine crews. Douglas Earle Marsh therefore sought to rebuild six examples with a larger boiler and cylinders in 1910. In the event, only one locomotive, number 79A, was rebuilt. This locomotive was known as D1X class, but although it was more powerful than the originals, it was found to be unsteady at speed and so no further rebuilds were authorised. Of the other five new boilers, one was used to rebuild E1 class no. 89 in 1911, and the other four were put to stationary use at various places on the LBSCR system. Post-grouping There were 84 D1 and D1X locomotives surviving in December 1922 at the grouping of the railways of southern England to form the Southern Railway. The class continued to find useful work on secondary services throughout the new railway, often in preference to far newer locomotives. During the Second World War six surviving examples were loaned to the London Midland and Scottish Railway and served in the north of Scotland. Nine examples were fitted with water pumps and firefighting equipment and were stationed at the major motive power depots in London to deal with incendiary