The sixth HMS Monmouth of the British Royal Navy was the lead ship of a class of armoured cruisers of 9,800 tons displacement. She was sunk at the Battle of Coronel in 1914.
Built in 1901, with her heaviest guns being fourteen 6 inch quick-firers, she had a weak armament for an armoured cruiser. In addition, most of the casemate 6 inch guns were situated so close to the waterline that they were unusable in all but the calmest weather. Her armour was also much too thin for an armoured cruiser and could be easily penetrated by artillery shells. These problems would prove disastrous for her thirteen years later at Coronel. She served on the China Station between 1906 and 1913, before being put in the Reserve Fleet in January 1914.
On the outbreak of the First World War she was reactivated and sent to the 4th Cruiser Squadron (the West Indies Squadron) of Admiral Sir Christopher Cradock. She participated in the Battle of Coronel off the coast of Chile on 1 November 1914. Outmatched and with an inexperienced crew, she was quickly overwhelmed, being unable to use many of her guns due to the stormy weather. Early in the battle, a 21 cm (8.2 inch) shell from SMS Gneisenau penetrated the armour of the forward 6 inch gun turret, destroying it and causing a massive fire on the forecastle. More serious hits followed, and she soon could no longer hold her place in the line of battle. When it was clear that Monmouth was out of action, Gneisenau shifted fire to HMS Good Hope. A short while later, drifting and on fire, Monmouth was attacked by the newly arrived light cruiser SMS Nürnberg under the command of Kapitän zur See Karl von Schönberg, which fired seventy-five 10.5 cm (4.1 inch) shells at close range. Monmouth and Good Hope both sank with a combined loss of 1,570 lives. There was no survivor from either ship.