HMS "Zealous" was laid down on 26 October 1859 as a wooden two-deck, 90-gun ship of the line by Pembroke Royal Dockyard, but her construction was suspended pending experience with the conversion of her half-sisters of the "Prince Consort" class to broadside ironclads. The Admiralty ordered on 2 July 1862 that she be cut down one deck and converted to an armoured frigate for the price of £239,258. The ship was launched on 7 March 1864 and commissioned in September 1866, but was not completed until 4 October 1866.