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The LSWR Class T10 4-2-2-0 was a prototype express steam locomotive design by Dugald Drummond for the London and South Western Railway introduced in 1897.

Background
Number 720 was a prototype locomotive built in 1897. The layout was unusual and evidently influenced by Webb's 3-cylinder compounds introduced in 1883 on the LNWR that employed two pairs of uncoupled driving wheels; the Drummond locomotives were always known as the "double singles".

Design features
Throughout locomotive history, this type of layout with independent uncoupled trains of driving wheels mounted on a common rigid chassis has been repeatedly tried with various aims in mind (the best-known more recent example is the Duplex locomotive). In the case of Drummond,the main motive in 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 beween the frames. This limited the width of the grate whilst its length depended on the distance between the coupled axles minus the throw of eventual inside cranks; at the same time there was a reluctance to make the coupling rods too long due to concern about material resistance, for a broken coupling rod flailing away under a locomotive could wreak tremendous havoc. One way out of the impasse was to eliminate the coupling rods altogether and to have two independent pairs of driving wheels each pair driven by its own cylinders. The first engineer known to have adopted this solution was Francis Webb, followed by Alfred de Glehn in France who initially combined divided drive and independent driving axles, finally opting solely for the former whilst coupling the driving wheels. The aforementioned engineers locomotives were compounds and the layout was also was a way of separating high-pressure from low-pressure drive trains; Drummond's 720 worked with simple expansion so that the principle benefit sought would be the increased grate area. Compared with Drummond's standard boilers, barrel length was increased from 10 foot 6 inches to 12 feet.

Rebuild
In 1905, number 720 was rebuilt with a larger boiler with the diameter increased from 4 foot 5.5 inches (1.4 m) to 4 foot 10.75inches (1.5 m). Tube heating surface went up from