[2][page needed] Joseph Beattie was the first to establish the LSWR's policy of using smaller wheeled locomotives to handle these steep gradients.

It soon became clear that despite the merits of the T9s for fast running on the various express passenger services to the west of England, the large wheels of the class were not suited for the task in hand.

The class was to incorporate the same frames as the T9, though smaller 6 feet 1 inch (1.854 m) driving wheels were substituted, whilst they also had balanced crank axles.

[2][page needed] All locomotives were fitted with the Drummond "watercart" eight-wheel tender for longer running on the LSWR network.

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

[3][page needed] The boiler was mounted higher above the frames, which led to instability concerning the ride of the locomotives at high speeds.