The s were an enlargement of the earlier Algerine-class gunboats of 1856. The British Admiralty ordered the first pair of the class as "new style steam schooners" on 1 April 1857; a further order for three took place on 27 March 1858. A sixth was ordered on 8 April 1859. The naval dockyards constructed all six; all were re-classified as second-class gunvessels on 8 June 1859.
The Admiralty ordered a further twelve of the class on 14 June 1859 with this new classification, including the Mullett, and they received their names on 24 September. They were constructed of wood in contract yards and then fitted out at naval dockyards. A final eight were later ordered from the naval dockyards, although six of these were subsequently cancelled.[1]
Mullett was laid down at the Rotherhithe yard of Charles Lungley on 29 June 1859 and launched on 3 February 1860. She was fitted with a Robert Napier & Sons two-cylinder horizontal single-expansion steam engine driving a single screw and developing 355ihp.[1]
She was fitted out at Deptford Dockyard, and this would have included her armament of a 68-pounder 95 cwt muzzle-loading smooth-bore gun, two 24-pounder howitzers and two 20-pounder breech-loading guns. All ships of the class later had the 68-pounder replaced by a 7-inch/110-pounder breech-loading gun. The class were fitted with a barque-rigged sail plan.[1]
After commissioning at Sheerness on 30 April 1862, she sailed for the West Africa Squadron under the command of Commander Cortland Herbert Simpson. She stayed there for a number of years and participated in at least one punitive expedition.
On an evening in October 1862, open mutiny broke out in the Gold Coast Artillery Corps at Cape Coast. The authorities dispatched Mullett to Accra to forestall a similar outbreak. There was no loss of life. Although 80 mutineers were court martialled and two were sentenced to death, their sentences were commuted.[2]
On 28 June 1866, Mullett, under Captain Robinson, and in company with the small colonial steamer Dover, landed a force of about 400 British troops under Colonel D'Arcy, primarily from the West India Regiment, at Bathurst in the Gambia. The force, joined by local allies, stormed a Marabout stronghold after Mullett had ineffectively shelled the stockade with her 68-pounder for four hours. The British suffered several dead in their attack.[3]
From 7 November 1867 Commander Edward Kelly commanded Mullett on the North America and West Indies Station. In 1869, while the ship was in Jamaica, Able Seaman William Wardell won a Royal Humane Society Bronze Medal for saving the life on 10 June of Robert Cleal, an armourer of . Cleal had fallen overboard and Wardell jumped in, holding Cleal above water until a lifebuoy was thrown to him. Cleal was unconscious when brought aboard Mullett but was revived.[4] Mullett paid off at Sheerness on 19 July 1870.[5]
The Admiralty sold her in Hong Kong on 25 April 1872 for mercantile use. She had her engines removed by W Walker & Co of London, converting her to a barque-rigged sailing vessel. Under the name Formosa she made several voyages to the Antipodes.
Ultimately she was purchased at Melbourne. Then during the Russian war scare in the late 1880s, the government of Victoria bought several old vessels, including Formosa as blockships for the south and west channels. The scare passed and in 1890 the government converted Formosa to a magazine.[6]