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From the start the KGV class was to be armed with sixteen of the new 5.25"/50 Mk I guns in twin mounts. This new weapon was intended to be the largest practical size for a hand loaded medium gun. With 80# projectiles, the work was heavy - but the biggest factor was the size of the turrets, with the large rounds, there wasn't much room. The rate of fire was about half what was hoped for, and about a third what the USN 5" guns could deliver, the rate of train and elevation on the mount was also insufficient -given the trend towards faster aircraft. The later Vanguard addressed the problem to some degree with larger and faster moving turrets, but the improvement was less than hoped for. Ballistically the gun was very good, comparing favorablely to other heavy AA guns.
Early in the Japanese attack on PoW and Repulse (Force Z) on 12/10/41 a Japanese torpedo struck the PoW where the propeller shaft enters the hull, a very lucky hit. The damage was extreme, and included loss of power to the 5.25" guns, which could not be worked for the remainder of the action, denying the new weapons the chance to demonstrate their effectiveness in the critical action. This failure of a modern battleship in action and underway was far more damaging to the reputation of the battleship than the recent destruction of unprepared fleets at anchor (at Taranto and Pearl Harbor). The battleship proponents had been claiming that it was impossible to sink a battleship that was underway and fighting back - this action destroyed that myth.
Several of these guns were subsequently deployed in large coastal defense turrets with autoloaders and exhibited outstanding performance (after the war) - but the days of the heavy AA gun had already passed and they were superceeded by missiles. Some interesting experiments were done with the rifling on these later guns, the grooves tapered down to a smooth bore near the muzzle to groom the projectile's driving band and make it more aerodynamic for better range and accuracy.
5.25”/50 QF MKI: The 5.25 was an effort to field the heaviest practical DP gun, and this weapon debuted on the King George V battleships. The separate loading ammunition with an 80# shell proved too heavy for the manual loading in the cramped turrets on these earlier ships. This was compounded by slow training and elevation and reliability issues with the mounts and the gun was generally unsuccessful on WWII ships. The gun had a MV of 2600 fps and an effective ceiling of 46.5000 ft, the KGV class and Dido class cruiser had a ROF of 7-8 rpm. The designed ROF was 12 rpm which was never achieved, the barrels lasted for about 750 rounds, and were of a conventional multi-tube construction but did not use a liner. The problems were corrected on small number of land mounted army guns, and the later HMS Vanguard had enlarged gun houses with faster elevation and training as well as an improved 9-10 rpm ROF The 5.25” twin mounts weighed about 1.5x as much as the more effective 4.5” versions, which could deliver a much greater weight of fire by virtue of their higher ROF, had the KGV used the 4.5” it could have carried 24 guns instead of the 16 she did carry. The few land based army versions had higher MV and very large turrets, these were used in coastal batteries. A proposal was made in 1944 for a fully automatic naval version with fixed ammunition, and a ROF of 70 rpm, the design was never built (HMS Vanguard would have been even more impressive had she been built with these guns).
Pictures: 1. 5.25" guns on PoW. 2. Gunhouse on KGV, 3. Deck view of 5.25" mount on Pow, 4. Howe turning at speed 1943, 5. Superstrucure detail of KGV
Note: the Pom Pom came in two versions the standard and the HV version introduced in 1938, unfortunately the HV version was not much better than the standard version. The idea of these was to put up a wall of fire, since hitting the target was not likely with this weapon. http://www.navweaps.com/Weapons/WNBR_2pounder_m8.htm
PoW and Repulse in their final action
The Quad version, mounted on the B and X turrets soon replace by octuples. Note the ammo in the feed trays, which is less than half the length of the Bofors gun ammo of the same caliber - and less than half as powerful.
King George V himself - The class was named after him at the request of King George VI
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