Battlecruisers – both over-gunned and under-armoured

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Matthew Wright

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I'm a New Zealand historian with a life-long interest in matters military, particularly naval engineering. My books have principally been published by Penguin Random House. I'm a Fellow of the Royal Historical Society at University College, London.
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We popularly envisage ‘battlecruisers’ as heavily armed but badly armoured – trading speed for protection. That criticism was particularly levelled at Britain’s first ships of the type, which emerged from the same Committee on Designs that produced the Dreadnought in the first months of 1905 and, in essence, created the battlecruiser as a type, although the term did not enter common use for some years. Their heyday was the First World War.

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HMS Invincible – more super-scale armoured cruiser than anything else.

But were these first examples of the type, particularly, under-armoured – or are we better to call them over armed?

The actual answer is ‘both’. This is clear from their origins. By the turn of the twentieth century, armoured cruisers had emerged as lighter-armed and armoured but faster homologues of contemporary battleship designs. And they followed the trend to up-arm heavy warships with intermediate batteries. During 1903, Admiral Sir John Fisher, as C in C of Portsmouth dockyard, worked with the yard Constructor, W. H. Gard, to draw up a variety of conceptual warships, including a better armoured cruiser, ‘Untakeable’, which they envisaged carrying four 9.2-inch and a dozen 7.5-inch guns, all at 25 knots.

The Admiralty were already moving down this path: by 1904, armoured cruisers had fewer of the qualities needed for colonial patrol duties and had instead become effectively a second-class battleship – more lightly armed and armoured, but still with good punch, and significantly faster than contemporary battleships.  They were also approaching the same size and cost. When the Committee met, Britain’s latest armoured cruiser, Sir Phillip Watts’ Minotaur, displaced 14,600 tons and carried four 9.2-inch and ten 7.5-inch guns at 23 knots with a 6-inch armoured belt. That compared to the equivalent battleship, Lord Nelson, which displaced 15,358 tons and carried four 12-inch and ten 9.2-inch at 18 knots. At the expected battle ranges of the day – 3000 to 6000 yards – the 9.2-inch was capable of penetrating most known armour, and there was talk of using the armoured cruisers in the battle line as fast units to harry the enemy van.

This is the key point – ships, both then and later, were designed to fight at specific ranges. These were later quantified as the ‘immunity zone’, within which armour was designed to be proof to specific weights of shell. Usually, for the purpose of balancing the design, the ship’s own main armament was taken as the measure. But even around the turn of the twentieth century, naval architects were aware of the issues. And at that time, the expected battle ranges produced heavy fire at fairly flat trajectories, demanding side armour, but not deck protection to the same extent.

In December 1904, less than two months after becoming First Sea Lord, Fisher formed a Committee on Designs to consider what ships the Royal Navy should build. Pressure was on to give battleships all-big gun armament, partly because of fire-control problems when dealing with shell splashes from mixed armament. Japan and the United States were already designing such battleships – so it was inevitable that the Committee’s proposed battleship, HMS Dreadnought, followed suit. This ship has been covered in an earlier article of mine.

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HMS Minotaur (1906) with her original short funnels.

The committee then turned their attentions to the armoured cruiser. Here there was potential for an all-9.2-inch armed ship; but the committee swung to 12-inch guns in part, it would seem, because the Japanese were building four large armoured cruisers mounting four 12-inch and a battery of 6-inch, the Tsukuba class. In January 1905, as Fisher’s Committee met, the last two were re-designed to carry eight 8-inch guns instead of the 6-inch.  The Committee may have been aware of it, but in any event the only reply to the Tsukuba was to match the main battery calibre. Japan was an ally; but that wasn’t the point.

The resulting ship was not based on Dreadnought; she was a 12-inch gunned , turbine-driven edition of Minotaur, sharing many of the characteristics. In particular, the Committee specified armour no heavier than that of Minotaur, which itself had reduced armour by comparison with its predecessors. This was unfortunate. The 6-inch belt may have been (just) adequate for an armoured cruiser, but it fell short against 12-inch shells. Watts, as designer of the new ships, was later criticised for under-armouring the Invincibles; but as he pointed out, he had been given that specification. Part of the reason was keeping displacement (hence cost) within bounds, and even then the design displacement at 17,300 tons was fairly comparable to Dreadnought, the first time armoured cruisers had matched battleships.

The other part of the calculation is that lack of armour did not initially seem an issue. They were reasonably protected against armoured cruiser fire and Fisher thought speed was protection against anything heavier: at 25 knots. He also convinced the Admiralty to build more. Although just one Dreadnought was laid down in wake of the Committee’s recommendations, the Admiralty also committed to three Invincibles. Their build-times were not accelerated, unlike Dreadnought; but the fact that three of them were laid down speaks volumes.

So – under-armoured or over-gunned? Opinion of the day and later was under-armoured; but if we look at general large-ship trends of the day, the Invincibles were within bounds in terms of speed, displacement and armour – all of which had been rising in armoured cruisers. Watts basically produced a next-generation Minotaur, with the same armour and higher speed, indicating an evolutionary process. The stand-out was their armament. Although the echelon arrangement for the midships turrets meant only six of their eight twelve-inch guns could usefully fire on any broadside, these weapons – the largest available at the time – were disproportionately heavy by armoured cruiser standards. The ships were, in short, over-gunned. And that made their armour inadequate against the usual measure, their own main armament. That said, given the Japanese trend, it is difficult to see Fisher’s Committee accepting a 9.2-inch gunned vessel; and the other option – upping the displacement – was politically unacceptable.

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Profile of the Invincible, from Brassey’s Naval Annual 1923. Public domain, via Wikipedia.

The fact that a 12-inch armament was discontinuous with armoured cruiser trend is underscored by the fact that although the three Invincibles were not publicised, it was impossible to hide the fact that they were being built. In order to obscure their true fire-power, the Admiralty put about  misinformation that they were armed with 9.2-inch guns. This was credible – an armoured cruiser homologue of Dreadnought, logically, would be so armed. So the Germans ‘replied’ with an armoured cruiser carrying a dozen 8.2-inch, the Blucher.

But even when the true details of the Invincible became known, the German response was not a direct imitation. Their first true battlecruiser, Von der Tann of 1908, was slower than the British vessels, less heavily armed – but had a 9.8-inch belt and better armour protection, on displacement of 19,064 tons. The real problem of the Invincibles – and their successors, the Indefatigables, a mildly modified version of the same design –  was that they were too small for the characteristics being packed into them. The issue was political: Britain’s Liberal government was trying to get naval budgets down – and even on constrained displacement, each Invincible still cost nearly half as much again as a Minotaur.

The problem in service was that 12-inch guns gave them the status of a battleship, a point picked up by the public and reflected in changing nomenclature. Invincible and her two sister ships were initially known as armoured cruisers. However, by the time the Lion came along in 1909 the type was being referred to as a ‘battleship cruiser’, or sometimes a ‘dreadnought cruiser’. By 1912 that had become ‘battle cruiser’, and finally ‘battlecruiser’. Both these and battleships were then given the blanket term ‘capital ships’, disguising the fact that battlecruisers had never been intended to sit in the battle line.

Superficially the results were disastrous. Even the 9-inch armour given to later British battlecruisers was vulnerable to heavier German shells. Three British battlecruisers along with the Minotaur-class cruiser Defence blew up at Jutland when they came under fire. The Hood, the last British battlecruiser completed, blew up in 1941 after engaging Bismarck in the Denmark Strait. Popularly, these losses were put down to lack of armour. That played a part, but – and as always with complex machinery – the specifics were not simple. Other battlecruisers, notably Lion and Tiger, took a pounding without sinking – a dozen or more heavy hits that left them battered and burning, but without serious loss of buoyancy, speed or fire-power. Recent water-tank tests with a buoyancy-correct model of HMS Queen Mary, flooded to the same extent as Seydlitz after Jutland, showed that Queen Mary – too – could have survived the same loss of reserve buoyancy that was suffered by the German battlecruiser, which returned to Wilhelmshaven after Jutland with over 5000 tons of water aboard and her bows level with the water.

In fact Queen Mary blew up and sank in a minute. Was inadequate armour a problem? Or was the situation more complex? I‘ve covered that story in my book Dreadnoughts Unleashed – which has the tale of the Jutland losses and much more. So if you enjoyed this article and want to read more on this, and on general naval engineering and history, don’t forget to check it out on Kindle.

Copyright © Matthew Wright 2017

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