[1] Unlike its French and Italian contemporaries of similar size the QF 5.25-inch gun was designed as dual-purpose equipment capable of engaging both aircraft and surface targets.

Combining the secondary and heavy anti-aircraft armament allowed a significant weight savings for the King George V-class battleships, which were designed to meet the Washington Naval Treaty limit of 35,000 tons.

[8] In comparison, the French 138 mm (5.4 in) Mle 1934 guns as used on the Mogador-class destroyers had a maximum range of 21,872 yd (20,000 m) at 30 degrees with an 88 lb (40 kg) SAP shell.

[9] The Italian 135/45 mm gun as used on the Capitani Romani-class cruisers had a maximum range of 21,435 yd (19,600 m) at 45 degrees with a 72.1 lb (32.7 kg) AP shell.

[12][page needed] However HMS Spartan, a Bellona-class cruiser (Improved Dido), was sunk at anchor in 1944 by a Luftwaffe guided missile.

[13][14][15] However, these factors do not appear to have reduced Euryalus's rate of fire, over a one-minute period, which was typical for a World War II AA engagement.

[14][note 3] Nevertheless, these elevation and traverse rates were still higher than some contemporary weapons, such as the 10.5 cm SK C/33 twin mounts carried on the German battleships Bismarck and Tirpitz.

Trials and use led the army to design a single gun mounting in two marks, both with an underground engine room to provide electrical and hydraulic power for traverse, elevation, fuze setting, ramming and other tasks.