215, 217 The two ships were virtually identical to the preceding London sub-class of the Formidables and are generally considered part of the Formidable Gibbons, p. 151 or London class, Chesneau & Kolesnik, p. 37 Parkes, p. 408 but the difference in the distribution of their 12-pounder 3 inches guns, their lower displacement, and their later construction than the Duncans lead some authors to view them as constituting a Queen class separate from the Formidable and London classes.