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.

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.

[5][6] Rising international demand for coffee and rubber in the early 20th century brought Brazil an influx of revenue.

[4] Simultaneously, the Baron of Rio Branco spearheaded a drive by prominent Brazilians to force the leading world nations to recognize Brazil as an international power.

[9] 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.

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.

[11][B] By May 1911, Fonseca had made up his mind: 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.

[18] The steam plant consisted of twenty-two Babcock & Wilcox water-tube boilers with an operating pressure of 235 psi (1,620 kPa; 17 kgf/cm2).

[17] Agincourt mounted fourteen BL 12-inch Mk XIII 45-calibre guns in seven twin hydraulically powered turrets,[19] unofficially named after the days of the week, starting from Sunday, forward to aft.

They fired 850-pound (386 kg) projectiles at a muzzle velocity of 2,725 ft/s (831 m/s); at 13.5°, this provided a maximum range of just over 20,000 yards (18,000 m) with armour-piercing (AP) shells.

[22] 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.

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.

[25] Agincourt had another weakness in that she was not subdivided to Royal Navy standards as the Brazilians preferred to eliminate all possible watertight bulkheads that might limit the size of the compartments and interfere with the crew's comfort.

[30] Approximately 70 long tons (71 t) of high-tensile steel was added to the main deck after the Battle of Jutland to protect the magazines.

[25] Rio de Janeiro, as Agincourt was named by her first owners, was laid down on 14 September 1911 by Armstrongs in Newcastle upon Tyne and launched on 22 January 1913.

[17] After the keel-laying, the Brazilian government found itself in an unenviable position: a European depression after the end of the Second Balkan War in August 1913 reduced Brazil's ability to obtain foreign loans, while at the same time Brazil's coffee and rubber exports collapsed, the latter due to the loss of the Brazilian rubber monopoly to British plantations in the Far East.

[33] Renamed Sultân Osmân-ı Evvel, she underwent trials during the July Crisis the following year and was completed in August, just as the First World War was beginning.

"[35] At the same time, the British also took over a second Ottoman battleship, a King George V class-derived vessel being built by Vickers—Reşadiye—which was renamed HMS Erin.

The seizure, and the gifts of the German battlecruiser Goeben and the cruiser Breslau to the Ottomans, influenced public opinion in the Empire to turn away from Britain, and they entered the war on the side of Germany and the Austro-Hungarian Empire against the Triple Entente of Britain, France, and Russia on 29 October, after Goeben had attacked Russian facilities in the Black Sea.

[39] Her name, "Agincourt", was a favourite of Churchill's, and had initially been allocated to a sixth vessel of the Queen Elizabeth class ordered under the 1914–15 Naval Estimates, but not yet begun at the war's outbreak.

[41] The Admiralty was unprepared to man a ship of Agincourt's size on such short notice and her crew was drawn "from the highest and lowest echelons of the service: the Royal yachts, and the detention barracks."

This was the beginning of "a year and a half of inaction, only broken by occasional North Sea 'sweeps' intended to draw the enemy from his bases.

[45] Admiral Jellicoe, commander of the Grand Fleet, kept it in cruising formation until 18:15,[D] when he ordered it to deploy from column into a single line based on the port division, each ship turning 90° in succession.

Shortly afterwards her six-inch guns followed suit as German destroyers made torpedo attacks on the British battleships to cover the turn to the south of the High Seas Fleet.

[50] In the reduced visibility the division lost sight of the Grand Fleet during the night, passing the badly damaged battlecruiser SMS Seydlitz without opening fire.

[51] Dawn found them with only the detritus from the previous day's battle in sight and the division arrived back at Scapa Flow on 2 June.

[56] The conversion was cancelled on 23 February 1922 after the Washington Naval Treaty was signed that limited the battleship tonnage allowed to the RN and she was paid off on 7 April and listed again for disposal.

The Admiralty agreed that cutting the hull in half would be acceptable and the company attempted to move the ship through the dockyard locks on the highest Spring Tide to its beaching ground to complete the demolition.

Bad weather thwarted that effort and the Admiralty agreed to allow the use of one of Rosyth's dry docks to meet the deadline.