HMS Agincourt was a battleship with a complex, albeit not particularly long, history.
The ship was ordered as the Brazilian battleship Rio de Janeiro in June 1911, with the country locked in an arms race against the other two most powerful South American neighbours, Argentina and Chile. Brazil in fact did start the arms race in 1906 with the order of two brand-new Minas Geraes class dreadnoughts, the third country to do so after Britain and the USA. The Argentinians responded by ordering two of their own, the Rivadavia class, all with 12'' (305 mm) guns, while Chile ordered in 1910 two massive superdreadnoughts with 14'' (356 mm) weapons modelled on the new Orion class.
Both Brazilian and Argentinian ships had twelve guns each, but both were forced to respond to Chile's powerful warships in terms of better ones and hull numbers. And so Brazil looked into British yards' proposals for a third dreadnought of their own, to counter this new threat. That dreadnought was eventually named Rio de Janeiro, and exhibited quite the peculiar look: seven turrets with fourteen 12'' guns dotted the silouhette of the ship, the Brazilians initially wanting to go for bigger guns, but retaining instead the now ubiquitous 12'' calibre due to budgetary constraints; the number of barrels was increased to compensate compared to their previous ships. The result was one of the most unique battleships ever built, and the one with the most number of turrets and guns.
Laid down in mid-September 1911, launched in January 1913, the ship would be put up for sale in October because a national financial crisis left no funds to pay for the ship. The Ottomans, preoccupied by the Greek Navy's interest in obtaining a dreadnought, bought the ship (now renamed Sultan Osman-i Evvel) for almost £3 million. However, a conflict that would later be dubbed 'the Great War' broke out in August 1914, during her sea trials.
Not wanting the ship to potentially be used against them, British authorities seized the battleship along with a second Ottoman vessel (Resadiye, later renamed HMS Erin), which caused considerable resentment in Turkey as these ships had been partially funded by public subscription. These actions later influenced the Ottoman Empire's involvement in World War I.
As for the ship, she was taken in Royal Navy service, renamed once again to HMS Agincourt, and crewed mainly with reservists as there were not enough crew to man all the ships available in such a short time.
Agincourt joined the 4th Battle Squadron of the Grand Fleet in September 1914 but her service career was fairly uneventful: her most notable action is the battle of Jutland, where she fired 144 main battery shells, though it is unclear whether she ever hit a target.
Present at the surrender of the High Seas Fleet in November 1918, it was quickly placed in reserve in Rosyth in March 1919. The Royal Navy decided to convert her into a mobile naval base, after unsuccessful attempts to sell her back to Brazil. However the Washington Naval Treaty prevented her retention by Britain, and so Agincourt was scrapped in 1924.