The class D-8 consisted of 20 4-4-0 Camelback locomotives built in the Reading's own shops between 1898 and 1911. They were ordered after George W. Cushing had been unable to persuade the railroad that conventional narrow firebox locomotives were better than anthracite-burning Camelbacks with Wootten fireboxes. So they were built again with the same firebox as the D-5 with a grate area of 76 square feet, but a longer boiler barrel. 

The first seven D-8a were built in 1898 and had drivers of 68.5 inches and a boiler pressure of 160 psi. Five years later the Reading built three D-8b which had the same boiler, but drivers of 74 inches, a pressure of 200 psi and a cylinder diameter that had been increased by half an inch. The ten D-8c built in 1911 again had smaller drivers of 68.5 inches, a larger firebox and tubes with a greater diameter.

In 1920 and 1922, five D-8c were superheated and designated D-8sd. In the same process, their Stephenson valve gear was replaced by one of the Walschaerts type. Most non-superheated locomotives were gone by the mid-thirties. The last D-8c survived until 1940 and the D-8sd were retired some years later.