page_title: Formidable-class battleship
section_title: Armament and armour
hierarchical_section_title: Formidable-class battleship / Design / Armament and armour
caption_attribution_description: Right elevation diagram of 12-inch Mk IX gun turret of British Formidable class battleship. Guns are loaded at elevation of 4½°. A chain rammer is used.
context_page_description: The Formidable class of battleships were a three-ship class of pre-dreadnoughts designed by Sir William White and built for the Royal Navy in the late 1890s. The class comprised Formidable, Irresistible, and Implacable. They were armed with a battery of four 12-inch guns, they had top speed of 18 knots, and they marked the adoption of Krupp armour in British battleship designs. The class formed the basis for the nearly identical London class of five ships, and those ships are sometimes included in the Formidable class. Formidable, Irresistible, and Implacable were built between 1898 and 1901 at the Portsmouth, Chatham, and Devonport Dockyards, respectively.
  All three ships served in the Mediterranean Fleet early in their careers, before returning to British waters in the late 1900s for duty in the Home Fleet, Channel Fleet, and the Atlantic Fleet. By 1912, all three ships had been assigned to the 5th Battle Squadron, Home Fleet, where they remained until the outbreak of the First World War in August 1914.
context_section_description: Formidable and her sisters had four 12-inch (305 mm) 40-calibre Mk IX guns mounted in twin-gun turrets fore and aft; these guns were mounted in circular barbettes that allowed all-around loading or elevation. Shell allowance was 80 rounds per gun. The Formidable class were the first to carry these guns, which featured several improvements over the earlier Mk VIII guns used in older battleships, including a stronger barrel design and higher muzzle velocity. Formidable and Implacable had BVI type mountings for their guns, while Irresistible received newer BVII mounts, the primary difference between the two types being the arrangement of the shell hoists and other equipment. Both types of mountings had a range of elevation from -5 degrees to of 13.5 degrees. The BVI mounts required the guns to return to 4.5 degrees to be loaded, while the BVII mounts allowed for loading at any angle. The guns had a muzzle velocity of 2,562 to 2,573 feet per second (781 to 784 m/s), and they were capable of penetrating 12 inches of Krupp armour at a range of 4,800 yards (4,400 m). At their maximum elevation, the guns had a range of 15,300 yards (14,000 m). The guns had a rate of fire of one shot every eighty seconds.
  The ships also mounted a secondary battery of twelve 6-inch (152 mm) 45-calibre guns mounted in casemates, which were supplied with 200 rounds per gun. The guns had a muzzle velocity of 2,536 ft/s (773 m/s). These guns could penetrate 6 inches of Krupp armour at 2,500 yards (2,300 m). Maximum elevation was 14 degrees, which allowed the guns to engage targets out to 12,000 yards (11,000 m). For close-range defence against torpedo boats, they carried ten 12-pounder guns with 300 rounds per gun and six 3-pounder guns with 500 shells per gun. As was customary for battleships of the period, they were also equipped with four 18-inch (460 mm) torpedo tubes submerged in the hull.
  The Formidable-class ships made more extensive use of Krupp steel than the preceding Canopus class, with most of their side armour consisting of the stronger steel. They had an armoured belt that was 9 inches (229 mm) thick and extended from the forward main battery barbette to the aft barbette; the transverse bulkheads on either end of the belt were 9 in thick forward and 9 to 10 in (229 to 254 mm) thick aft. The belt extended from main deck level (9 ft 6 in (3 m) above the waterline) to 5 ft 6 in (2 m) below the waterline. The ships' side plating forward of the belt was 3 in (76 mm) thick, while it was only 1.5 in (38 mm) aft of the belt. The ships were fitted with two armoured decks; the first was a flat deck that was 1 in (25 mm) thick, above the main deck, which was 2 in on the flat portion and increased slightly to 3 in on the sloped sides, where it connected to the belt armour.
  The ships' main battery turrets sides and faces were 8 in (203 mm) thick—reduced slightly compared to earlier ships to account for the heavier belt armour—with 10 in (254 mm) thick rears. The turret roofs were 3 in thick. The turrets sat atop 12 in thick barbettes, though Irresistible's barbette armour was reduced in thickness to 10 in behind the belt. Above the main belt was a strake of armour that protected the casemate guns, which was 6 inches thick; behind the casemates, an interior bulkhead that was 2 in (51 mm) thick protected the interior of the ship. Their forward conning tower had 10 to 14 in (254 to 356 mm) thick sides, with a communication tube below the tower that had armour protection that was 8 in (203 mm) thick. The aft conning tower had 3 in thick sides with a 3 in tube below.
caption: Right elevation of 12 inch gun turret & ammunition hoists
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