This was the first 0-6-0 tank design of William Dean and in its concept and dimensions may be regarded as the precursor of all the larger GWR pannier tanks of the 20th century, such as the 5700 and 9400 classes:
Wheels 4 ft 6 in (1.37 m) diameter, wheelbase 15 ft 6 in (4.72 m)
From 1894 some of the 1813s were rebuilt with saddle tanks, and in 1903-6 six were rebuilt with either short or full-length pannier tanks, resulting in a very early example of this type of engine. The rest were so converted between 1911 and 1925, as had become standard practice on the Great Western. The class also carried an unusually wide variety of different boilers.