The "Diadem" class was designed to protect British merchant shipping from fast cruisers like the Russian and were smaller versions of the . The ships had a length between perpendiculars of , a beam of and a draught of . They displaced . The first batch of "Diadem"s were powered by a pair of four-cylinder triple-expansion steam engines, each driving one shaft, which were designed to produce a total of and a maximum speed of using steam provided by 30 Belleville boilers. They carried a maximum of of coal and their hulls were sheathed with copper to reduce biofouling. Their complement numbered 677 officers and ratings.