The Prince Consort class of ironclad battleship were four Royal Navy wooden-hulled broadside ironclads: HMS Royal Oak, HMS Prince Consort, HMS Ocean, and HMS Caledonia. They were originally laid down as , but were converted to ironclads. Royal Oak was Britain's fifth ironclad battleship completed. Prince Consort, Ocean, and Caledonia were built to a common design and are today known as the Prince Consort class, though contemporaries knew them as the Caledonia class. Royal Oak was their half-sister. Genesis The of nine 91-gun two-decker steam line-of-battle ships were laid down between March 1859 and October 1860 (a further three were ordered, but never laid down, and eventually cancelled in 1863). Their dimensions were the same as (101 guns), but had a new timbering plan to suit the smaller armament. The reduction in armament was intended to improve the efficiency of the guns. Bulwark and Robust were suspended in March 1861 in an advanced state of construction and were eventually broken up in March 1873 and August 1872 respectively. The remaining seven ships of the Bulwark class were less complete state and were converted into 'ironclad frigates'. Of these Triumph (later renamed Prince Consort), Ocean, and Caledonia were converted to 'broadside ironclads' with 1,000 nhp engines. Royal Oak had a similar conversion but with the original 800 nhp engine. Royal Alfred, Zealous and Repulse were later converted into 'central battery ships'. Reasons for the conversion programme When the first British ironclads were conceived, the Surveyor (Rear Admiral Sir Baldwin Wake Walker) said, "They must be regarded as an addition to our force, as a balance to those of France, and not as calculated to supersede any existing class of ship; indeed no prudent man would, at present, consider it safe to risk up the performance of ships of this novel character, the naval Supremacy of Great Britain." For this reason, the Royal Navy continued to lay down and complete steam two-deckers and three-deckers. However, in 1861, it was clear that Britain was falling behind in ironclads laid down (see table below). The ten French ironclads laid down in 1861 were the start of the French programme of 1860, which was intended over a number of years to produce: 20 sea-going ironclads for the active fleet, 10 sea-going ironclads for the reserve fleet, and 11 floating batteries. The British response to the French programme was taken in a number of steps. On