The class 1076 tank locomotives were actually built for the GWR standard-gauge routes and had a double frame, i.e. they had both outside and inside frames and the wheels were between them. The first six had simple side water tanks, but all others were built with a saddle tank. In the first batch, the cab was only protected by a weather board, in the later batches there was a cab that was open at the back. Later, completely closed driver's cabs were retrofitted, since tank locomotives often ran backwards.

In 1876, ten locomotives were built for the seven feet broad gauge, with the wheels outside the outer frame. Five more followed two years later and from 1884 a total of 35 of the standard-gauge engines were rebuilt in the same way. When operations on the broad-gauge lines were discontinued, the locomotives were restored to standard gauge and thus joined the remaining 216. Most of the surviving machines were even modernized from 1911 and got Pannier water tanks. The latter got their name from the panniers carried by pack animals and were popular with the GWR. The previous saddle tanks could no longer be accommodated in the engines that had been retrofitted with a Belpaire firebox with an angular external profile.