The LSWR Class T7 4-2-2-0 was a prototype express steam locomotive design by Dugald Drummond for the London and South Western Railway introduced in 1897.

The layout was unusual and influenced by Francis Webb's 3-cylinder compound locomotives introduced in 1883 on the London and North Western Railway (LNWR) that employed two pairs of uncoupled driving wheels; the Drummond locomotives were always known as the "double singles".

In the case of Drummond, the main motive appears to have been to obtain maximum grate area in a period where low-pitched boilers were the norm and the firebox had to be set low between the frames.

The aforementioned engineers' locomotives were compounds, and the layout was also a way of separating high-pressure from low-pressure drive trains.

Drummond's T7 and E10 worked with simple expansion so that the principal benefit sought would be the increased grate area.