Inconstant was the first of an intended six fast, unarmoured, iron-hulled, frigates designed by the British Admiralty's Chief Constructor, Sir Edward Reed, in response to the fast, wooden American Wampanoag-class frigates. Only three were built, however, as the American ships proved to be flawed enough to pose no real threat and the British ships were very expensive.^[3] The ship was 337 feet 4 inches (102.8 m) long between perpendiculars, had a beam of 50 feet 3 inches (15.3 m), and a draught of 25 feet 6 inches (7.8 m). Inconstant displaced 5,780 long tons (5,870 t)^[4] and had a tonnage of 4,066 tons burthen. She carried a complement of 600 officers and ratings.^[5] To reduce biofouling, her iron hull was sheathed in two layers of oak 3 inches (76 mm) thick that was covered by a layer of copper. Inconstant was a good seaboat and a steady gun platform.^[6]

The ship had a single John Penn and Sons two-cylinder trunk steam engine that drove a 23-foot (7.0 m) propeller. The engine used steam provided by 11 boilers with a working pressure of 30 psi (207 kPa; 2 kgf/cm²).^[1] Inconstant reached a speed of 16.2 knots (30.0 km/h; 18.6 mph) from 7,360 indicated horsepower (5,490 kW) during her sea trials and was the fastest warship afloat when completed.^[4] The ship once sustained an average speed of 15.5 knots (28.7 km/h; 17.8 mph) for 24 hours.^[7] She carried a maximum of 750 long tons (760 t) of coal, enough to steam 2,780 nautical miles (5,150 km; 3,200 mi) at 10 knots (19 km/h; 12 mph).^[5]

Inconstant was ship-rigged with three masts and a sail area of 26,655 square feet (2,476 m²). She proved to be excellent under sail, reaching a maximum speed of 13.5 knots (25.0 km/h; 15.5 mph), one of only two warships ever to reach this speed under sail and 16 knots with steam.^[8] To improve her performance under sail, her propeller could be hoisted into the hull and her funnels lowered to reduce drag.^[4]

When completed the ship was more heavily armed than all but two of the twenty-four British ironclads afloat.^[1] Inconstant's main armament consisted of ten rifled muzzle-loading (RML) 9-inch (229 mm) guns on the main deck in the traditional broadside layout.^[5] The 9-inch shells weighed 254 pounds (115.2 kg) and were rated with the ability to penetrate 11.3 inches (287 mm) of wrought-iron armour.^[9] Her secondary armament of six RML 7-inch (178 mm) guns was mounted on the upper deck, with two guns positioned in the bow as chase guns.^[1] The guns fired a 112-pound (51 kg) shell that could pierce 7.7 inches (196 mm) of armour.^[4]

Inconstant, the fifth ship of her name to serve in the Royal Navy,^[10] was laid down on 27 November 1866 at Pembroke Dockyard, Wales. The ship was launched on 25 March 1872 by Lady Muriel Campbell, daughter of John Campbell, 2nd Earl Cawdor. Inconstant was transferred to Portsmouth Dockyard to finish fitting out and was commissioned on 12 August 1869 by Captain Elphinstone D'Oyly D'Auvergne Aplin for duty with the Channel Squadron.^[11] He was relieved by Captain Charles Waddilove on 13 September 1870.^[12] The following year the ship was assigned to the Detached Squadron, commanded by Rear-Admiral Frederick Seymour, which visited ports in Scandinavia after Inconstant joined them at Gibraltar, finally arriving at Spithead on 11 October 1871.^[13] The ship was paid off in 1872 and spent the next eight years in reserve.^[14]

She was recommissioned in 1880 and was commanded by Captain Lord Walter Kerr from 5 February to 11 March. During this time, Inconstant served as the flagship of Vice-Admiral Seymour of the Mediterranean Fleet^[12] as she ferried replacement crews to that fleet.^[1] From August 1880 to October 1882, Inconstant was assigned to the reconstituted Detached Squadron, this time as the flagship, first of Rear-Admiral Richard Meade, 4th Earl of Clanwilliam until he was got sick in Hong Kong,^[15] and then from 6 December 1881 to 17 October 1882 of Rear-Admiral Sir Francis Sullivan.^[16] Inconstant's captain at this time was Captain Charles Penrose-Fitzgerald. The Detached Squadron left Spithead on 17 October 1880 to circumnavigate the world and returned two years later.^[13] It is claimed that on 11 July 1881 (or 11 June 1881^[17]), Prince George of Wales (later King George V of the United Kingdom) sighted a phantom ship whilst aboard Inconstant between Melbourne and Sydney. Two other ships, Tourmaline and Cleopatra, also reported seeing the phantom ship.^[18] Just after arriving in the Falkland Islands, the squadron was ordered to Simonstown, South Africa, for possible service in the First Boer War of 1880–81, but hostilities had already ended by the time that it arrived. On the return voyage, the frigate caught fire; it was stopped by flooding all of the after compartments. Shortly afterward, the squadron was diverted to Egypt after the start of the Anglo-Egyptian War of 1882; they arrived after the Bombardment of Alexandria on 11 July and some of Inconstant's crew were landed to participate in operations ashore.^[19]

The ship was reduced to reserve again after their return on 16 October 1882. She became an accommodation ship for the overflow from the barracks at Devonport in 1897.^[2] Inconstant was taken out of service in 1904 and became a gunnery training ship in June 1906, assigned to the boy's training establishment Impregnable.^[20] She was renamed Impregnable III in 1907, then Defiance IV in January 1922 after she was transferred to the torpedo training school at Plymouth, Defiance, and then Defiance II in December 1930. The ship was sold for scrap in September 1955 and arrived at the breaker's yard in Belgium on 4 April 1956 for demolition, when she was the second-to-last Welsh-built naval vessel afloat.^[2]

• Ballard, George A.; Admiral (January 1934). "British Frigates of 1875: The Inconstant and Raleigh". Mariner's Mirror. XXII (1): 42–53.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Brown, David K. (2010). Warrior to Dreadnought: Warship Development 1860–1905. Barnsley, UK: Seaforth Publishing. ISBN 978-1-78383-019-0.
• Colby, C. B. (1959). Strangely Enough, Sydney: Oak Tree Press ISBN 0-8069-3918-4
• Chesneau, Roger & Kolesnik, Eugene M., eds. (1979). Conway's All the World's Fighting Ships 1860-1905. Greenwich, UK: Conway Maritime Press. ISBN 0-8317-0302-4.
• Colledge, J. J.; Warlow, Ben (2006) [1969]. Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8.
• Gardiner, Robert, ed. (1992). Steam, Steel and Shellfire: The Steam Warship 1815–1905. Conway's History of the Ship. London: Conway Maritime Press. ISBN 1-55750-774-0.
• Parkes, Oscar (1990). British Battleships (reprint of the 1957 ed.). Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-075-4.
• Phillips, Lawrie; Lieutenant Commander (2014). Pembroke Dockyard and the Old Navy: A Bicentennial History. Stroud, Gloucestershire, UK: The History Press. ISBN 978-0-7509-5214-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
• Winfield, R.; Lyon, D. (2004). The Sail and Steam Navy List: All the Ships of the Royal Navy 1815–1889. London: Chatham Publishing. ISBN 978-1-86176-032-6. OCLC 52620555.

• Inconstant on Battleships and Cruisers
• The Flying Squadron
• Richard Charles Francis Meade on-line biography
• Frederick Beauchamp Paget Seymour on-line biography
• Sir Francis Sullivan on-line biography