For express trains on more hilly main routes, such as Devon and Cornwall, William Dean envisaged 4-4-0 locomotives with a coupled wheel diameter of five feet and eight inches. Based on his Duke class, he built No. 3312 “Bulldog” in 1898 with a larger boiler. Like the Duke, it had an outer frame that had recesses in the area of the cranks of the coupling rods. The boiler also had a steam dome, but the new boiler caught the eye with a raised Belpaire firebox. 

No. 3707 “Francis Mildmay”, later No. 3417 “Lord Mildmay of Flete”

The boiler was designed by George Jackson Churchward, who was still Dean's assistant at the time. The boiler was to become the GWR's standard boiler No. 2 and initially had a consistent diameter from back to front. In October 1899, No. 3352 “Camel” was completed, which is considered the first production example of the Bulldog class. With it, the boiler no longer had a steam dome and tapered from the back to the front.

No. 3733 “Chaffinch” from the Bird class

Locomotive Magazine, June 1909

In the following years several series were created, which showed some differences among themselves. Some continued to have a parallel boiler and others had a tapered boiler of varying design. Soon, the tapered boiler prevailed, as well as straight outer frames. Although the locomotives were initially referred to as the Camel class due to the first production engine, the prototype's name "Bulldog" soon caught on.

By 1909, 141 Bulldog-class examples had been built, 20 of which had been converted from existing Duke-class locomotives. In 1909 and 1910, another 15 examples of a slightly modified design, known as the Bird class, were built. It differed from the Bulldog class mainly in higher outer frames, a new bogie and a longer smoke box.

All locomotives of the two classes were retrofitted with a superheater between 1910 and 1914. Since the 4-4-0 locomotives of the GWR were initially provided with different number ranges across the classes, they were renumbered in 1912. The locomotives of the Bulldog and Bird classes received the number range between 3300 and 3455 without gaps. In August 1929, the first machine of the Bulldog class was decommissioned, but the decommissioning did not take place in larger numbers until 1934 and the last example survived until 1951. From of the Bird class, the first example only disappeared in 1948, but the last one also in 1951.