In the period just before I World War the arms race of the future opponents was speeding up. British First Sea Lord, admiral John „Jackie” Fisher, was a strong supporter of a battlecruiser doctrine. It was the concept of warships with main battery guns similar to those of dreadnoughts and more powerful engines allowing them to reach higher speeds.
All that, was at the expense of armour, which was insufficient and, in the future, would be the cause of many losses. Soon, new classes of battlecruisers were created. In 1909 and 1910, two Lion class units (HMS Lion, HMS Princess Royal) were laid down. They were the first ships to be armed with 13.5-inch battery. Their design evolved into the battlecruiser HMS Queen Mary, built as the only ship of its class.
Queen Mary was similar to the Lion class battlecruisers to such an extent that they are described by many sources as sister ships. In reality she was heavier and beamier than her predecessors. She had an improved power plant and armour. The ship was laid down, as a part of the 1910-11 program, on 6 March 1911 at Palmers Shipbuilding and Iron Company in Jarrow. The construction process was fast, and she was launched on 20 March 1912. In August 1913 the ship was completed and ready for service. Queen Mary was the last British battlecruiser built before the Great War.
The main battery of Queen Mary was the same as that of the Lion class. It constituted of eight 13.5-inch BL Mk V guns. It was the latest heavy gun of the Royal Navy. Solid construction of the barrel made the gun very accurate, reliable, safe and guaranteed low rifling wear. After the first tests, it became apparent that there was a considerable safety margin. That allowed the gun to be adapted for firing a heavier projectile than originally planned. Queen Mary mounted new, heavier Mk V (H) version of the gun. The results of test firing 635 kg projectiles were very satisfactory. The 13.5-inch guns were twin-mounted in four turrets which were a larger and improved version of turrets used for 12-inch guns. The “A” and “B” turrets were installed traditionally – on the foredeck in superposition, the “Q” turret was at the midships, separating the two boiler rooms, the “X” turret was on the low stern deck. The turrets had a system allowing the guns to be loaded at every elevation angle. At first, the system was discussed as space and weight consuming but the need to re-aim the guns after each reload convinced the designers to retain it.
Initially, the fire control posts were to be placed on the stern superstructure and on the bow mast. However, the mast smoking, caused by the first funnel placed closer to the bow, on the newly built Lion, forced design modifications. Positions of the first funnel and the bow mast were switched but, due to that modification, the director could not be mounted on a high platform. Finally, two 9-foot Argo rangefinders were installed on the conning tower behind the “B” turret and on the stern fire control post. Those were well armoured areas but they were too close to the waterline to track targets effectively. Queen Mary was the first battlecruiser to receive 9-foot rangefinders for each gun turret. Therefore, if communication with the fire control was lost, they could acquire and engage targets individually. Maximum elevation angle of the guns was 20° although the rangefinders could only operate within 15° range. It was due to the assumption that all battles would be fought at short distances only slightly exceeding 10,000 meters. That drawback was fixed before the Battle of Jutland. At the same time, the structure of the foremast was altered in order to mount the main battery director.
Queen Mary had a strong secondary battery whose task was to engage small but deadly targets – torpedo boats. It consisted of sixteen 4-inch guns on single mounts. The ship’s predecessors had their deck guns vulnerable to enemy fire and weather conditions so it was decided to provide the guns with better protection. The bow battery of eight guns was mounted in casemates and armoured, the eight guns mounted on the stern superstructure were protected by thin plating on the sides and top.
As nobody predicted the plane to become a dangerous adversary, the ship’s designers did not see the need to mount anti-aircraft artillery. When Queen Mary entered service, her only small calibre artillery were four, not very effective, Hotchkiss 3-pounders used mainly as saluting guns. They were placed on the stern superstructure deck, at the mast base. In October 1914, one 3-inch and one 6-pound anti-aircraft gun was fitted and the redundant 3-pounders finally disappeared from the battlecruiser’s deck at the beginning of 1915.