During this period, she was damaged in a pair of accidents, the first a collision with HMS Albion in late 1905 and the second when she ran aground off Lundy Island the following year.

After the outbreak of the First World War in August 1914, Duncan was being refitted; once she returned to service in September, she joined her sister ships on the Northern Patrol.

To achieve the higher speed while keeping displacement from growing, White was forced to reduce the ships' armour protection significantly, effectively making the ships enlarged and improved versions of the Canopus-class battleships of 1896, rather than derivatives of the more powerful Majestic, Formidable, and London series of first-class battleships.

The Duncans proved to be disappointments in service, owing to their reduced defensive characteristics, though they were still markedly superior to the Peresvets they had been built to counter.

The Duncan-class ships were powered by a pair of 4-cylinder triple-expansion engines that drove two screws, with steam provided by twenty-four Belleville boilers.

[3] Duncan had a main battery of four 12-inch (305 mm) 40-calibre guns mounted in twin-gun turrets fore and aft.

[2] HMS Duncan was laid down by Thames Ironworks and Shipbuilding Company, Leamouth, on 10 July 1899, and launched on 21 March 1901.

She suffered another mishap on 23 July 1906, when she grounded off Lundy Island during unsuccessful operations to salvage the battleship HMS Montagu.

[6] In July, Duncan visited Canada during the Quebec Tercentenary, in company with her sister ships Albemarle, Exmouth, and Russell.

On 27 May 1913, Duncan recommissioned at Chatham with a nucleus crew and was assigned to the 6th Battle Squadron in the Second Fleet at Portsmouth, where she served as a gunnery training ship in the commissioned reserve.

[6] Plans originally called for Duncan and battleships Agamemnon, Albemarle, Cornwallis, Exmouth, Russell, and Vengeance to form the 6th Battle Squadron in wartime and serve in the Channel Fleet, where the squadron was to patrol the English Channel and cover the movement of the British Expeditionary Force to France.

However, due a lack of antisubmarine defenses at Dover, particularly after the harbour's anti-submarine boom was swept away in a gale, the squadron returned to Portland on 19 November 1914.

Instead, Revel decided to implement a blockade at the relatively safer southern end of the Adriatic with the main fleet, while smaller vessels, such as the MAS boats, conducted raids on Austro-Hungarian ships and installations.

In February, Duncan returned to the United Kingdom and paid off at Sheerness to provide crews for antisubmarine vessels.

Duncan was placed on the disposal list in March 1919, and was sold for scrapping to Stanlee Shipbreaking Company Limited, in Dover, on 18 February 1920.