In the mid-1840s, the Admiralty ordered four iron-hulled, screw-driven frigates from specialist shipbuilders; however, the Admiralty then rapidly lost faith in the ability of iron hulls to stand up to combat conditions, and all four ("Greenock", "Vulcan", "Megaera" and "Simoom") were converted while under construction into troop transports, although the "Greenock" was promptly sold for commercial use.