[2] The ship was first British ironclad to be completed below her designed displacement; this meant that she was top heavy and required 360 long tons (370 t) of cement ballast to raise her metacentric height.

[4] Audacious had two 2-cylinder horizontal return connecting rod steam engines made by Ravenhill, each driving a single 16-foot-2-inch (4.9 m) propeller.

The bronze four-bladed Mangin propellers were not arranged in the usual radial cross shape, but rather in two pairs, one behind the other, on an elongated boss in an attempt to reduce their drag when the ship used her sails.

The engines produced a total of 4,021 indicated horsepower (2,998 kW) during sea trials on 21 October 1870 and Audacious reached a maximum speed of 12.83 knots (23.76 km/h; 14.76 mph).

The ship carried 460 long tons (470 t) of coal,[5] enough to steam 1,260 nautical miles (2,330 km; 1,450 mi) at 10 knots (19 km/h; 12 mph).

After the loss of HMS Captain in a storm in 1870, the ships were modified with a barque rig which reduced their sail area to 23,700 square feet (2,202 m2).

[7] They were slow under sail, only 6.5 knots (12.0 km/h; 7.5 mph),[8] partly due to the drag of the twin screws, and their shallow draft and flat bottom meant that they were leewardly when close-hauled.

The winds caught the rear of the ship as she was about halfway down the slipway and twisted her enough that some plates and frames of her bottom were damaged.

[15] Upon completion she became guard ship of the First Reserve at Kingstown, Ireland (modern Dún Laoghaire), but was transferred the following year to Hull where she remained until 1874.

The ship was ordered to the Far East that year to serve as the flagship for the China Station under the flag of Vice-Admiral Sir Alfred Phillips Ryder.

[19] She transferred to Felixstowe early the following year,[20] and acted as depot ship for destroyers in the Eastern district until 1905, when she paid off; in April 1904 she had been renamed Fisgard (after the French translation of the Welsh town Fishguard).

On 13 January 1915, the auxiliary minesweeper HMS Roedean was driven onto Imperieuse in Scapa Flow off Hoy, Orkney Islands; Rodean sank due to damage she suffered in the collision.