This was done in response to the perceived threat to Britain offered by the large French ironclad building programme.

The ship was ordered to the West Coast of Canada after she was completed to represent British interests in the Eastern Pacific Ocean.

HMS Zealous was given a straight stem and a rounded stern, but her hull was otherwise unmodified from her original form; it had been found that lengthening the hull, as was done in the earlier Prince Consort class, led to longitudinal weakness.

She also carried less armour than the earlier class, and was nearly a knot slower; however, as she was built to serve in distant waters, and not expected to face opposing ships of significant force, these shortcomings were thought acceptable.

[10] 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[11] that she be cut down one deck and converted to an armoured frigate for the price of £239,258.

In January 1870 she picked up a fresh crew at Panama brought out by the two-decker HMS Revenge.

Her bottom had not been cleaned since she had left Great Britain and she could only make a maximum of 7 knots (13 km/h; 8.1 mph) under sail or steam so her return voyage took five months.

Zealous struck a rock while sailing through the English Narrows in the southwestern coast of Chile, but was only slightly damaged.