The Deck-Armoured Battlecruiser
Anyone could build a fast, well-armed, well-armoured ship on forty or fifty thousand tons, but to build one on 23,000 tons must surely mean that it would be a lesser vessel; a second-rate battleship, or a poorly armoured battlecruiser?
In 1924, few thought that it could be done. Even the men who did it, didn’t think that it was a certainty when they started their work. In classical terms, it wasn’t possible, but a combination of new technologies, new ideas and a willingness to accept that not everything on a ship had to be protected equally meant that it was shown to be achievable; with every accountant’s trick and sea-lawyer’s fiddle, there were literally tons to spare.
Design ‘1924-B/3’ had shown that a powerful ship could be built on 23,000 tons (particularly if the designers ‘cheated’ by planning to add up to 3,000 tons of improvements to torpedo protection and air-defence later). However, the weight of the four armoured turrets made it a marginal design.
In the New Year of 1925, two ideas came together. One was the concept of limiting the protection of a ship to a well-armoured citadel around the waterline, rather than trying to extend heavy armour far up the hull. The other was the consideration that damage to armament could be tolerated, providing such damage did not automatically result in the loss of the ship.
Both at the Battle of Stavanger and in other, smaller actions, ships had been lost due to progressive flooding, torpedo hits or (most probably) to shells penetrating and exploding inside their magazines. Providing there were adequate means to prevent fires spreading from turrets to magazines, a hit on a turret would not destroy a ship; it would merely reduce its fighting ability. If it were essential to save weight, it was therefore a legitimate design choice to reduce armour on areas other than magazines and accept the risk that turrets might be lost.
Associated with that was a new weight and labour-saving mechanism that had been proposed a few months earlier, by the armaments firm Vickers. They proposed simplifying (and lightening) the usual multi-stage system of below-deck handling rooms, shell bogies, lower hoists, turret handling rooms and upper hoists.
In their new system steps would be eliminated or combined, and more of the process would happen below the armour deck.
Deep in the ship, a series of ‘cages’ (one for each gun above) would be filled through flash-tight scuttles from the magazines, and by fixed rammers for the projectiles. The cages would be sitting on a combined hoist and turntable, which would then raise them up to the level of the armour deck while simultaneously turning them from the fore-aft loading position of the magazines until they matched the train angle of the turret above.
Unlike in traditional turrets, the heavy armour deck would extend through the barbette, and a central disk of this thick deck would turn with the turret. Once correctly orientated, the ‘cages’ would pass through holes in this deck, each of which was surrounded by a short armoured trunk . Now above the armoured citadel, the charges and shell would still be protected, as each cage would rise into a splinter-proof armoured hood which would be waiting for it. The cage would latch into the hood and the whole unit would then be lifted up, allowing flash-tight shutters to close the holes below as the hood rose out of the armoured trunk.
The cage and hood would rise all the way up to the gun by a traditional winch hoist, before shell and charge ramming took place as usual.
The amount of handling machinery was reduced, but there was no opportunity to arrange the shells and charges between upper and lower hoists. They therefore had to be inserted in the cage in the correct order, with the shell and the bottom and the charges on top. This meant the magazines would return to their pre-war position above the shellrooms.
The system eliminated the handling room below the turret and the shell bogies, saving considerable space and weight. However, it meant that all guns had to be loaded together, as the below-armour hoist and turntable would supply of all the turret’s hood/cage assemblies simultaneously.
If the magazines were safely isolated behind heavy armour, turret protection could be reduced.
However, one of the ship’s primary missions was to destroy cruisers, and it would be absurd if the main armament could be knocked out by a cruiser’s guns.
The three main turrets were therefore protected by a 7” faceplate, with 3” sides and rear, while barbettes would be 5” where exposed, reduced to 3” inside the hull. This would keep out 8” gunfire at practical battle ranges and would also be ample proof against splinters from larger shells. The only exceptions were the roofs of the turrets, which had only a ½” weatherproof plate ‘as designed’. A 5½” thick plate would later be added on top as part of permitted improvements in horizontal armour.
Away from the citadel, the ships were only ‘protected’, rather than armoured.
Above the armour deck the sides of the ship had 2” of protective plating over their 1” skin, in a similar fashion to a light cruiser. To improve resistance to flooding near the waterplane, the double hull also covered this space between the main and upper decks, and a thin layer of armour would be added to the edges of the foc'sle, justified as part of improvements to bomb protection.
Armour scheme, with and without improvements.
The ships were designed so that they would not be ‘inconvenienced’ by 8” fire, but they also had to be safe to fight battleships. The objective here was to ensure that battleships could be engaged at certain ranges, without the Captain having to concern himself over the immediate safety of his ship.
As the scouting force of a fleet, or in a pursuit action, or when trying to turn the head of an enemy line, the ships would engage enemy battleships at relatively long ranges. At these ranges, the deck presented a larger target than the shallow belt needed to protect the machinery and magazines, and was therefore of relatively high importance.
The machinery was armoured against 15” gunfire, with the 9” inclined belt capable of resisting the 1,920-lb shells at ranges above 19,000 yards, and the 3½” thick deck providing protection below 22,500 yards.
It was vital that the magazines be proofed against the heaviest gunfire, which the ships’ Chief Designer, Charles Coles, defined as the 2,340-lb shell that was fired at 2,450fps by the British 16” Mk.2 gun. Why he did not choose the higher-performance Mk.2* is something of a mystery, although there wouldn’t have been any weight to spare for any additional armour if he had.
An 11”, 20-degree inclined belt would defeat these shells above 17,500 yards, and a 4” deck would keep them out below 23,500. This heavier armour also covered the transmitting station and part of the aft engine room, partly to guard against the possibility of end-on fire reaching the magazines.
If the Captain were able to keep the ship at an angle to the enemy, those minimum ranges could be reduced, but the design objective was the ships could be ‘safely fought’ on any course at ranges around 20,000 yards.