HMS Agincourt was a dreadnought battleship built in the United Kingdom in the early 1910s. Originally part of Brazil's role in a South American naval arms race, she holds the distinction of mounting more heavy guns (fourteen) and more turrets (seven) than any other dreadnought battleship, in keeping with the Brazilians' requirement for an especially impressive design.
Brazil ordered the ship in 1911 as Rio de Janeiro from the British company Armstrong Whitworth. However, the collapse of Brazil's rubber boom and a warming in relations with Argentina, the country's chief rival, led to the ship's sale while under construction to the Ottoman Empire. The Ottomans renamed her Sultan Osman I, after the empire's founder, and the ship was nearly complete when the First World War broke out. The British government seized her for use by the Royal Navy, together with another Ottoman dreadnought being constructed in Britain. This act caused resentment in the Ottoman Empire, as the payments for both ships were complete.
Renamed Agincourt by the Royal Navy, she joined the Grand Fleet in the North Sea. During the war, the ship spent the bulk of her time on patrols and exercises, although she did participate in the Battle of Jutland in 1916. Agincourt was put into reserve in 1919 and sold for scrap in 1922 to meet the terms of the Washington Naval Treaty.
Background
250px|left|thumb|Starboard elevation and plan view of Agincourt
thumb|left|Fantasy drawing of Sultan Osman I underway for the Ottoman Navy. The royal yacht [[:tr:MV Ertuğrul|Ertuğrul is at left, and the cruiser Hamidiye is in the background.]]
In the unstable period during and following the 1889 coup in Brazil, which deposed Emperor Dom Pedro II, and the 1893–94 navy revolt, the Brazilian Navy found itself unable to care for its own ships, let alone acquire new vessels. Meanwhile, Chile had agreed to a naval-limiting pact in 1902 with Brazil's principal rival, Argentina, as part of solving a larger boundary dispute, but they both retained the vessels built in the interim, many of which were significantly more modern and powerful than Brazil's ships. The Brazilian Navy was left behind its Argentine and Chilean counterparts in quantity as well—by the turn of the 20th century, Chile's total naval tonnage was , Argentina's , and Brazil's —even though Brazil had nearly three times the population of Argentina and almost five times that of Chile.
Rising international demand for coffee and rubber in the early 20th century brought Brazil an influx of revenue. The National Congress of Brazil inaugurated a large naval acquisition program in late 1904. They ordered three small battleships in 1906, but the launch of caused the Brazilian Navy to reconsider their purchase. In March 1907, they signed a contract for three s. Two ships would be constructed immediately by the British companies Armstrong Whitworth and Vickers, with the third to follow.
Alarmed at the Brazilian move, Argentina and Chile quickly nullified their 1902 pact and sought dreadnoughts of their own. Since Brazil's relations with Argentina were warming and the country's economic boom was losing steam, the government negotiated with Armstrong to remove the third dreadnought from the contract, but without success. They borrowed the necessary money, and Armstrong laid down Rio de Janeiros keel in March 1910.
The Brazilian Navy had divided into two distinct factions, based on the size of the main battery. The outgoing naval minister favoured an increase over the 12-inch guns mounted on board the Minas Geraes class, while his incoming counterpart, Admiral Marques Leão, favoured keeping the smaller but faster-firing gun. While the exact influences upon the Brazilian government are unclear, Leão was advocating strongly for his position in meetings with President Hermes da Fonseca. Other events probably influenced them as well, such as the November 1910 Revolt of the Lash, payments on loans taken out for the dreadnoughts, and a worsening economy that had led to high government debt compounded by budget deficits. By May 1911, Fonseca had made up his mind:
<blockquote>When I assumed office, I found that my predecessor had signed a contract for the building of the battleship Rio de Janeiro, a vessel of 32,000 tons, with an armament of 14 in. guns. Considerations of every kind pointed to the inconvenience of acquiring such a vessel and to the revision of the contract in the sense of reducing the tonnage. This was done, and we shall possess a powerful unit which will not be built on exaggerated lines such as have not as yet stood the time of experience.</blockquote>
A contract to build the ship that would become Agincourt was signed on 3 June 1911, and its keel was laid on 14 September 1911. The design called for fourteen 12-inch guns, an extreme number that historian David Topliss attributed to political necessity: the ship had to appear more powerful to the Brazilian populace than her predecessors (with twelve 12-inch guns) but, without increasing the gun size, the only option left was increasing the total number of guns.
Design and description
General characteristics
Agincourt had an overall length of , a beam of , and a draught of at deep load. She displaced at load and at deep load. The ship had a metacentric height of at deep load. She had a large turning circle, but manoeuvred well despite her great length. She was considered to be a good gun platform.
When she came to serve in the Royal Navy, Agincourt was considered a particularly comfortable ship and very well-appointed internally. A knowledge of Portuguese was necessary to work many of the fittings—including those in the heads—as the original instruction plates had not all been replaced when she was taken over by the British.
The steam plant consisted of twenty-two Babcock & Wilcox water-tube boilers with an operating pressure of . Agincourt normally carried of coal, but could carry a maximum of , as well as of fuel oil to be sprayed on the coal to increase its burn rate. At full capacity, she could steam for at a speed of . Electrical power was provided by four steam-driven reciprocating electrical generators.
Armament
thumb|right|upright=1.2|Sultan Osman-ı Evvel, soon to become Agincourt, in the [[fitting-out stage of her construction]]
Agincourt mounted fourteen BL 12-inch Mk XIII 45-calibre guns in seven twin hydraulically powered turrets, unofficially named after the days of the week, starting from Sunday, forward to aft. This was the largest number of turrets and heavy guns ever mounted on a dreadnought battleship. The guns could be depressed to −3° and elevated to 13.5°. They fired projectiles at a muzzle velocity of ; at 13.5°, this provided a maximum range of just over with armour-piercing (AP) shells. During the war the turrets were modified to increase their maximum elevation to 16°, but this only extended the range to . The rate of fire of these guns was 1.5 rounds per minute. When a full broadside was fired, "the resulting sheet of flame was big enough to create the impression that a battle cruiser had blown up; it was awe inspiring." No damage was done to the ship when firing full broadsides, despite the common idea that doing so would break the ship in half, but much of the ship's tableware and glassware did shatter when Agincourt fired her first broadside.
As built, Agincourt mounted eighteen BL 6-inch Mk XIII 50-calibre guns. Fourteen were placed in armoured casemates on the upper deck and two each in the fore and aft superstructures, protected by gun shields. After the ship was seized by the British, two more were added abreast the bridge in pivot mounts, protected by gun shields. The guns could be depressed to −7° and elevated to 13°, later increased to 15°. They had a range of at 15° when firing a shell with a muzzle velocity of . Their rate of fire was about five to seven rounds per minute, but this dropped to about three rounds per minute after the ready ammunition was used up because the ammunition hoists were too slow or few to keep the guns fully supplied. About 150 rounds were carried per gun.
Close-range defence against torpedo boats was provided by ten 45-calibre quick-firing guns. These were mounted in the superstructure in pivot mounts and protected by gun shields. Agincourt also carried three British 21 inch torpedo| submerged torpedo tubes; one was on each beam and the last was in the stern. The water that entered the torpedo tubes when they were fired was discharged into the torpedo flat to facilitate reloading the tube and then pumped overboard. This meant that the torpedo crewmen would be operating in of water if rapid fire was required. Ten torpedoes were carried for them.
Fire control
Each turret was fitted with an armoured rangefinder in the turret roof. In addition, another one was mounted on top of the foretop. By the time of the Battle of Jutland in 1916, Agincourt was possibly the only dreadnought of the Grand Fleet not fitted with a Dreyer fire-control table. A fire-control director was later fitted below the foretop and one turret was modified to control the entire main armament later in the war.
The armour of the barbettes constituted a major weakness in Agincourts protection. They were 9 inches thick above the upper deck level, but decreased to 3 inches between the upper and main decks and had no armour at all below the main deck except for "Sunday" barbette (which had 3 inches), and "Thursday" and "Saturday" barbettes (which had 2 inches). The turret armour was 12 inches thick on the face, on the side and in the rear. The turret roofs were 3 inches thick at the front and 2 inches at the rear. The casemates for the secondary armament were protected by 6 inches of armour and were defended from raking fire by 6-inch-thick bulkheads.
Wartime modifications
Approximately of high-tensile steel was added to the main deck after the Battle of Jutland to protect the magazines. Two anti-aircraft guns were added to the quarterdeck in 1917–18. A rangefinder was added to the former searchlight platform on the foremast at the same time. A high-angle rangefinder was added to the spotting top in 1918.