The trans-Atlantic concept was changed to a coastal defence ship, so a very low freeboard of 4 feet 6 inches (1.37 metres) was specified.

The loss of HMS Captain in September 1871 led to concerns about the stability of turret ships, and a special committee was set up to determine their seaworthiness.

[5] Another change was to extend the armoured breastwork with un-armoured structure to the sides of the ship and carried aft to improve the stability at large angles of heel.

This greatly improved the crew comfort by adding extra accommodation and especially latrines, but since it was not armoured it would have been riddled in a battle, reducing the stability of the vessel.

Other tests involved taking it to sea to look for rough weather, in one trial waves of 20 to 26 feet (6 to 8 m) were encountered which gave the ship a 14-degree roll either way.

The ships were equipped with eight rectangular boilers powering two 2-cylinder trunk direct acting steam engines turning two shafts producing 6,650 indicated horsepower (IHP) under a natural draught (ND) for a designed speed of 13.75 knots.

[7] The ships carried 1,800 tons of coal giving a cruising range of 5,980 nautical miles at a nominal speed of 10 knots.

[4] The ships could remain at sea for approximately 12 days with fuel available to steam at full speed for a short duration.

The armour plating only applied to the breastwork portion of the ship, and the bow and stern sections were basically unprotected.

The ships had their boilers replaced with eight cylindrical locomotive type boilers powering two Maudslay 3-cylinder vertical triple expansion (VTE) steam engines turning 2 shafts producing 7,000 IHP under a forced draught (FD) for an increase in speed to 14 knots.

[4] The 35 and 38 ton MLRs were replaced with four 10-inch 32 calibre (25.4 cm) breech-loading (BL) naval guns mounted in twin Mark II turrets.

The concept of the ships was openly assailed by the British press and cost Sir Edward Reed his position as Chief Constructor.

[7] Both were modernized in 1891 and spent the next ten years as guard ships or in reserve being activated only for the annual summer manoeuvres.