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AUDACIOUS central battery ironclads (4, 1870 - 1871)


Iron Duke




Yard No


Laid down




Audacious   141 Napier, Govan 26.6.1867 27.2.1869 10.9.1870 torpedo depot ship 1902
Invincible (ex-Crescent)   142 Napier, Govan 28.6.1867 29.5.1869 1.10.1870 torpedo depot ship 1901
Vanguard (ex-Centaur)   366 Laird, Birkenhead 21.10.1867 3.1.1870 28.9.1870 collision 1.9.1875
Iron Duke   174 Pembroke DYd 23.8.1868 1.3.1870 21.1.1871 coal hulk 1900

Technical data

Displacement normal, t


Displacement full, t6010
Length, m

85.3 pp

Breadth, m


Draught, m


No of shafts



Audacious, Invincible, Iron Duke: sails + 2 2-cyl HSE, return connection rod, 6 rectangular boilers

Vanguard: sails + 2 2-cyl HSE, return connection rod, 3 rectangular boilers, 3 water-tube boilers

Power, h. p.

Audacious: 4020

Invincible: 4830

Iron Duke: 4270

Vanguard: 4910

Max speed, kts

Audacious: 12.8

Invincible: 14.1

Iron Duke: 12.6

Vanguard: 14.7

Fuel, t

coal 460 - 500

Endurance, nm(kts)

1260 - 1580(10)

Armour, mm

iron; belt: 203 - 152 with 254 - 203mm wood backing, battery: 152 - 102, bulkheads: 127 - 102


10 x 1 - 229/14 MLR Mk IV, 2 x 1 - 160/16 64pdr 71cwt MLR Mk III, 6 x 1 - 100/21 20pdr 16cwt BL (saluting)




<i>Iron Duke</i>
Iron Duke
<i>Audacious </i> after modernization
Audacious after modernization

Project history

Provided under 1867 Estimates, these 2nd class ironclads were designed for service on foreign stations. Construction was based on design of Defence but with more modern layout and shallow draught. Two-storey box battery was adopted and reductions were made in hull weight to secure a lower level of stability for a steady gun platform. They were rather too successful as 350t of ballast had to be added to improve stability but they did  prove exceptionally steady ships with almost no roll. There were 6 229mm guns in the main battery firing through broadside ports and 4 229mm guns in the upper battery firing also ahead and astern through corner ports. 160mm guns were mounted at ship ends on the upper deck.

Vessels were ship-rigged on completion but were converted to barque-rig in about 1871, with a sail area of 2200m2. They were very steady and good seaboats but made no more than 10kts under sail. Vanguard was equipped with half ordinary boilers and half water tube boilers. All except Iron Duke had balanced rudders. Audacious was zinc sheathed.

Invincible and Vanguard were renamed 30.4.1867 before keel laying. Fifth ship of the class was planned, initially named as Semiramis (since 30.4.1867 Bellona), but she was cancelled in August 1867 without going out to tender.

Ship protection

Ships had a narrow 2.4m-high waterline belt 203mm amidships and 152mm at the ends. The central battery on the main deck was 18m long with 152mm sides, 127mm fwd and 102mm aft bulkheads. The upper battery on the upper deck had 152mm armoured sides and corners only.


1878, all survived: + 4 - 356 TC

early 1880s, Invincible: - 2 x 1 - 160/16; + 6 x 1 - 102/27 BL Mk II/III/IV/V/VI

early 1880s, Audacious: received a military rig, light topmasts and fighting tops were fitted on the fore and main masts; - 2 x 1 - 160/16; + 8 x 1 - 102/27 BL Mk II/III/IV/V/VI, 4 x 1 -57/40 Hotchkiss QF Mk I, 6 x 1 - 47/40 Hotchkiss QF Mk I

early 1880s, Iron Duke: was re-engined and re-boilered (3520hp, 13.6kts, 700t of coal, 3900(10)nm); - 2 x 1 - 160/16; + 4 x 1 - 127/25 BL Mk I/II/III/IV/V

Naval service

Vanguard was accidentally rammed by Iron Duke 1.9.1875 during fog in Dublin Bay. She was rammed between the boiler and engine compartments, which flooded, sinking the ship in 70min. The loss was largely attributed to the lack of wing compartments. Audacious was converted to torpedo depot ship in 1902, renamed Fisgard in April 1904, converted to training ship 1.1.1906, later in 1914 converted to repair ship and renamed Imperieuse and sold for BU 12.3.1927. Invincible was converted to torpedo depot ship in 1901, renamed Erebus as training ship in April 1904, renamed Fisgard II in January 1906 and foundered in tow off Portland 17.9.1914. Vanguard was converted to coal hulk in 1900 and sold for BU 15.5.1906.

Thanks to Wolfgang Stöhr for additional information on this page.