In 1902, the GWR rebuilt a 4-4-0 Atbara class locomotive with a new domeless taper boiler with Belpaire firebox. This was No. 3405 “Mauritius”, which now served as a prototype for the new City class. Ten more of this type were built in 1903 with numbers 3433 to 3442. In 1907 and 1908, nine more Atbaras were rebuilt, bringing the number of the City class to 20. Soon they were given the numbers 3700 to 3719.

No. 3440 “City of Truro”, which later became 3717 and is considered the first steam locomotive to actually reach 100 mph or 161 km/h, achieved greater fame. This happened on the ninth of May 1904 on the Wellington Bank in Somerset, which had a gradient of 1 in 90. However, due to the inaccuracies of the measurement methods at the time, it is still not entirely clear whether the speed achieved was up to 102.3 or even just 99 mph. 

Between 1910 and 1912 all members of the City class received a superheater. Further modifications carried out over the years included the boiler feed, chimney, valves, a steam reverser and a different bogie. All machines were withdrawn between October 1927 and May 1931. Due to its history, the “City of Truro” is the only one that has been preserved and is now no longer operational.