Gradually evolving from the masted steam frigates of the mid-19th century, the first modern cruiser is not easy to define, but the starting point for this work is the construction of the Iris and Mercury of 1875. They were the Royal Navy's first steel-built warships; were designed primarily to be steamed rather than sailed, and formed the basis of a line of succeeding cruiser classes. This history ends with the last armored cruisers, which were succeeded by the first battlecruisers (originally called armored cruisers), and with the last Third Class Cruisers (Topaze class), all conceived before 1906. The only comprehensive study of cruisers in this era, it is heavily illustrated with rare photos, and detailed ship plans by A. D. Baker II.