The sole member of her class, Queen Mary shared many features with the Lion-class battlecruisers, including her eight 13.5-inch (343 mm) guns.

As part of the 1st Battlecruiser Squadron, Queen Mary attempted to intercept a German force that bombarded the North Sea coast of England in December 1914, but was unsuccessful.

She was hit twice by the German battlecruiser Derfflinger during the early part of the battle and her magazines exploded shortly afterwards, sinking her with the loss of more than 98 percent of the ship’s complement.

She differed from her predecessors of the Lion class in the distribution of her secondary armament and armour and in the location of the officers' quarters.

On sea trials in May and June 1913, Queen Mary achieved more than 83,000 shp (62,000 kW), although she barely exceeded her designed speed of 28 knots (52 km/h; 32 mph).

[11] Queen Mary mounted eight BL 13.5-inch Mk V guns in four twin hydraulically powered turrets, designated 'A', 'B', 'Q' and 'X' from bow to stern.

[12][13] They fired 1,400-pound (635 kg) projectiles at a muzzle velocity of 2,490 ft/s (760 m/s); at 20° elevation, this provided a maximum range of 23,740 yd (21,708 m) with armour-piercing (AP) shells.

[15] Her secondary armament consisted of sixteen BL 4-inch Mk VII guns, most of which were mounted in casemates on the forecastle deck, unlike the arrangement in the Lion class.

They fired 31-pound (14 kg) projectiles at a muzzle velocity of 2,821 ft/s (860 m/s) at a maximum range of 11,400 yd (10,400 m);[16] the ship carried 150 rounds per gun.

[17] The three-inch gun fired a 12.5-pound (5.7 kg) shell at a muzzle velocity of 2,604 ft/s (794 m/s) with a maximum effective ceiling of 23,000 ft (7,010 m).

One set was mounted in Queen Mary and consisted of a 9-foot (2.7 m) Argo rangefinder located on top of the conning tower that fed range data into an Argo Clock Mk IV (a mechanical fire-control computer)[20] located in the transmitting station below the conning tower.

Her aft torpedo director tower was protected by six-inch walls and a three-inch cast steel roof.

High-tensile steel torpedo bulkheads 2.5 inches (64 mm) thick were fitted abreast the magazines and shell rooms.

[28] Queen Mary's first action was as part of the battlecruiser force under the command of Beatty during the Battle of Heligoland Bight on 28 August 1914.

They turned south at full speed at 11:35[Note 2] when the British light forces failed to disengage on schedule, and the rising tide meant that German capital ships would be able to clear the bar at the mouth of the Jade Estuary.

Beatty, however, was distracted from the task of finishing her off by the sudden appearance of the elderly light cruiser SMS Ariadne directly ahead of him.

Beatty's main body encountered the crippled Cöln shortly after turning north, and she was sunk by two salvos from Lion.

An earlier Raid on Yarmouth on 3 November had been partially successful, but a larger-scale operation was devised by Admiral Franz von Hipper afterward.

The fast battlecruisers were to conduct the bombardment, while the entire High Seas Fleet was to station itself east of Dogger Bank to provide cover for their return and to destroy any elements of the Royal Navy that responded to the raid.

Together with the six dreadnoughts of the 2nd Battle Squadron, Beatty's 1st BCS – now reduced to four ships, including Lion – was detached from the Grand Fleet in an attempt to intercept the Germans near Dogger Bank.

[Note 3] This confusion allowed the German light cruisers to escape, and alerted Hipper to the location of the British battlecruisers.

[32] Queen Mary was refitting in January and February 1915 and did not participate in the Battle of Dogger Bank;[27] she received her main battery director in December 1915.

Two minutes later, he ordered a course change to east south-east to position himself astride the German's line of retreat and called his ships' crews to action stations.

Hipper ordered his ships to turn to starboard, away from the British, almost 180 degrees, to assume a south-easterly course, and reduced speed to 18 knots (33 km/h; 21 mph) to allow three light cruisers of the 2nd Scouting Group to catch up.

[33] This began what was to be called the "Run to the South" as Beatty changed course to steer east-southeast at 15:45, paralleling Hipper's course, now that the range closed to under 18,000 yards (16,000 m).

[35] During this period, Queen Mary made two hits on Seydlitz, at 15:55 and 15:57, one of which caused a propellant fire that burnt out her aft superfiring turret.

Cordite in the working chamber caught fire and produced poisonous fumes that asphyxiated some of the turret's crew.

[39] A further explosion, possibly from shells breaking loose, shook the aft end of the ship as it began to roll over and sink.