The LSWR D15 class 4-4-0 was the last steam locomotive design by Dugald Drummond for the London and South Western Railway in 1912.

The boiler was based on that fitted to the 1905 rebuild of his first double-single, T7 class number 720 of 1897; and had a long firebox with a sloping grate.

An exhaust steam feedwater heater was provided and the boiler fed by duplex pumps located on the frames, between the coupled wheels.

Contrary to Drummond's previous 4-6-0 designs, the D15s performed exceptionally well and were put to work on trains to Bournemouth, where many drivers noted their superior operational characteristics when compared to the T14 class 4-6-0s.

These successful locomotives worked, in the main, out of Waterloo and for a period prior to electrification had a virtual monopoly of the Portsmouth expresses, until the Schools class were introduced.

When transferred to Southern Railway ownership after 1923, the locomotives carried Richard Maunsell's darker version of the LSWR livery.