On 9 November 1918, just two days before the end of the war, she was torpedoed by a German submarine off Cape Trafalgar and sank with the loss of 50 men.

The new ships, though based on the general Majestic type that had formed the basis of the preceding four battleship designs, marked the first significant change in the series.

The King Edward VII-class ships were powered by a pair of 4-cylinder triple-expansion engines that drove two screws, with steam provided by sixteen water-tube boilers.

The King Edward VII-class ships had a top speed of 18.5 knots (34.3 km/h; 21.3 mph) from 18,000 indicated horsepower (13,000 kW).

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

[3][4] As was customary for battleships of the period, she was also equipped with five 18-inch (457 mm) torpedo tubes submerged in the hull; two were on each broadside, with the fifth in the stern.

[8] Upon the outbreak of the First World War in August 1914, the 3rd Battle Squadron, at the time under the command of Vice-Admiral Edward Bradford, was assigned to the Grand Fleet and based at Rosyth, where it was reinforced with the five Duncan-class battleships,[9][10] It was used to supplement the Grand Fleet's cruisers on the Northern Patrol.

[11] On 6 August, the day after Britain declared war on Germany, elements of the Grand Fleet sortied to inspect the coast of Norway in search of a German naval base violating Norwegian neutrality.

Four hours later, they met the 1st and 4th Battle Squadrons, en route from Scapa Flow, though they failed to reach the German High Seas Fleet before the latter withdrew.

The Grand Fleet remained at sea until late on 17 December, at which point the 3rd Battle Squadron was ordered back to Rosyth.

[17] On 23 January, the 1st and 2nd Battlecruiser Squadrons sortied to ambush the German I Scouting Group in what resulted in the Battle of Dogger Bank the following day.

The 3rd Battle Squadron patrolled the area with the rest of the Grand Fleet over the night before being detached at 08:00 on 25 January to steam to Rosyth.

She was stranded for 36 hours but was refloated; having suffered extensive damage, the ship required lengthy repairs at the Devonport Dockyard.

[6][19] On 29 April 1916, the 3rd Battle Squadron was rebased at Sheerness, and on 3 May it was separated from the Grand Fleet, being transferred to the Nore Command.

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.

[21] She underwent a refit at Gibraltar in February–March 1917, and on its completion was attached to the 9th Cruiser Squadron to serve on the Atlantic Patrol and on convoy escort duty, based mainly at Sierra Leone.

[8][22] On the morning of 9 November 1918, under the command of Captain Francis Wade Caulfeild,[23] Britannia was on a voyage in the western entrance to the Strait of Gibraltar when she was torpedoed off Cape Trafalgar by the German submarine UB-50.