The Minotaur class armoured frigates were essentially enlarged versions of HMS Achilles

HMS Achilles (1863)

The broadside ironclad HMS Achilles was the third member of the 1861 programme, was described as an armoured frigate, and was originally projected as a modified version of the earlier ....

 with heavier armament and armour, and more powerful engines.

The three vessels of the class - HMS Minotaur

HMS Minotaur (1863)

HMS Minotaur was the lead ship of the armoured frigates built for the Royal Navy during the 1860s. They were the longest single-screw warships ever built. Minotaur took nearly four years between her launching and commissioning because she was used for evaluations of her armament and different...

, HMS Agincourt

HMS Agincourt (1865)

HMS Agincourt was one of three Minotaur class ironclads, the sistership of HMS Minotaur and a near sister to HMS Northumberland...

 and HMS Northumberland were designed with a full-length strake of armour along the side to provide protection to all guns on the main deck. This necessitated an increase in length over HMS Achilles, and resulted in the class being the largest armoured ships ever to be propelled by a single screw.

All three ships took so long to complete after being laid down - Agincourt five years and four months, Minotaur seven years and three months, Northumberland seven years almost to the day - that by the time that they became operational their armament and armour was verging on the obsolescent, barely justifying their excessive initial cost or the resources deployed for subsequent alterations.

The ships of this class were unique among ironclad warships in possessing on completion five masts, named fore-, second-, main-, fourth- and mizzen.

They were the first British iron-hulled warships whose carrying capacity exceeded the weight of their hulls; 5,232 tons v 5,043 tons.

In the original design it had been intended to mount forty Armstrong 100-pounder breech-loader

100-pounder breech-loader

The Armstrong RBL 7 inch gun, also known as the 110-pounder, was an early attempt to use William Armstrong's new and innovative breechloading mechanism for heavy rifled guns.-Description:...

 cannon on the main deck, with ten more on pivot mountings on the upper deck. The failure of these guns in service led to a complete re-evaluation of the armament fit of these ships, with a significant concomitant delay in the arming of the whole class. The ships were initially armed with a combination of 9-inch muzzle-loading rifles

RML 9 inch 12 ton gun

The RML 9 inch guns Mark I - Mark VI were large rifled muzzle-loading guns used as primary armament on smaller British ironclad battleships and secondary armament on larger battleships, and also ashore for coast defence.-Design:...

 on metal carriages made to the design of Admiral Sir Percy Scott

Percy Scott

Admiral Sir Percy Moreton Scott, 1st Baronet GCB KCVO was a British Royal Navy officer and a pioneer in modern naval gunnery.-Early years:...

, and 7-inch muzzle-loading rifles

RML 7 inch gun

The RML 7 inch guns were various designs of medium-sized rifled muzzle-loading guns used to arm small-medium sized British warships in the late 19th century, and some were used ashore for coast defence.-Design and history:...

on rope-worked carriages. In a moderate swell these 7-inch guns were virtually unworkable, making the Minotaurs both the largest and the worst armed of the Victorian battleships.

When re-armed it was necessary, in order to accommodate the fewer but larger guns, to enlarge every alternate gun-port, including armour, iron backing and teak backing, using drills and cold chisels.

The Minotaurs were poor sailors, never exceeding a speed under sail of about 9.5 knots with all sail set and a favourable wind. They were, in spite of the number of masts they exhibited, the most sluggish of all British ironclads under sail

They were regarded as good sea-boats, and were considered to be among the steadiest ships in the battle-fleet. They were slow in manoeuvre under hand-steering, but were regarded as good after steam steering was fitted.