2013/02/03

Cruiser displacement development 1918-1945

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I was irritated by the recurring assertion about how cruisers of the period between the world wars supposedly grew to treaty limits (10,000 tons) and also about a less common assertion that light cruisers (CL) grew to the size of heavy cruisers (CA) during that period.

A book of mine ("Cruisers of World War Two" by M.J. Whitley) provided a handy source and I created a table file. This diagram is one outcome.

(Plotted was first ship of class only. Excluding classes with no unit completed prior to end of WW2. Excluding classes with first unit laid up prior to 1918. CL: Main gun calibre 5.5" to 6.1". CA: Main gun calibre 7.1" to 8". Dates are "laid up" dates.)

My suspicions were neither confirmed nor refuted (some did simply not build CA and CL in parallel for many years and the size of individual ship classes was often unintentional or driven by budget restrictions). 
The lower end outliers of the diagram (such as Tromp, Yubari) are rather destroyer leaders than full-blown CLs, while the two upper end CAs were two classes (Hipper, Baltimore) which stuck to the traditional CA calibre of about 8", but incorporated a fine protection against 8" unlike all other cruiser classes.

It's rather striking how heavy cruiser classes were mostly introduced during the 1925 - 1932 period and how light cruisers kept both a slightly lower displacement up to equal (almost the same hull for Brooklyn CL and Wichita CA). Mogami CLs were also meant to be up-gunned from 6" to 8", as was done after 1938.

Illustration of German CA Prinz Eugen, one of two ultimate CA classes of WW2
The size of these Inter-War Years cruisers was driven by design parameters (more than 30 kts top speed, varying degree of protection against destroyer and cruiser fire) and the need to combine at least a broadside of six shells. A smaller salvo was known to deliver not enough splashes for a good observation of the centre of impacts and thus no good centralised fire control (same story as with the 4x 12" gun pre-Dreadnoughts and the Dreadnought revolution). The very large CLs were usually armed with very many guns (12 or 15).
The five smallest CA classes had either the minimum of six guns of about 8" calibre or nine smaller 7.1" guns (Kirov class).
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The global diagram is interesting, but actual characteristics of admiralty procurement development only become visible on the national diagrams:


France built CAs at treaty limits and a couple of CLs at budget limits. They did develop super destroyers which bridged the gap to small CLs (2,610 tonne class and 2,930 tonne class), but don't appear in this diagram.  


Germany built light cruisers when they were allowed (replacements of older ships), but they were all contrary to pre-1918 shipbuilding tradition very fragile designs, looking stronger on spec sheets than they were. When allowed, they built some powerful heavy cruisers. I omitted the 11"-armed Panzerschiffe, an anomaly.


Italy built some ship classes for high top speed (fragile) and published exaggerated top speeds based on speed trials with much less than standard displacement. Only their latest cruiser classes were robust, and it shows in the CL weight gain.

Japan built a couple old-style CLs with 5.5" guns and one smallish experimental CL (Yubari). Some later ships were built under influence of treaty rules. Some ship classes suffered from a poor ability to withstand Hurricanes as discovered when their 4th fleet faced a hurricane (which rolled over a brand-new destroyer and badly mauled many other ships). I have no idea why they built a couple modestly-sized light cruisers during the 1940s.

The UK and Australia basically used the same designs and design philosophies due to the close integration of their navies. It's striking how they never built CLs and CAs in parallel.

The United States built a WWI-era CL class, then some poorly protected CA classes, and finally CLs and CAs quite in parallel. Their Treaty-era designs were remarkably close to the treaty limit of 10,000 tonnes.


The other navies built ships without treaty restrictions, but with severe budget restrictions. The smallish Dutch CLs were meant for rather short range actions in the Dutch colonies of Southeast Asia (now = Indonesia). Their Tromp class of '36 (6 x 5.9") was so small it was even officially called flotilla leaders (in Dutch, of course). The French super destroyers were very, very close to such a design (Mogador from 1934: 2,930 tons, 8x 5.47" guns and slightly better range).

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In the end, my attempt to confirm some suspicions met no decisive success, but I produced a table and stuff and thought it would be a waste to keep it to myself.


(The link won't stay active forever, as filehosters purge their servers from inactive files.)


S Ortmann

P.S.: Keep in mind some ships of up to almost 12,000 tons were actually meant to meet the 10,000 tons treaty limits. Some weight gain from drawing board to completion was unintended and sometimes some extra weight was considered to be moderate enough to be concealed from the other signatories.

P.S.2: In case you wondered why CLs kept existing at all; there's a watershed in rate of fire at about 6" calibre.
5.5" to 6.1" is the calibre area with the heaviest cartridges that allow rapid fire with manual loading. Bigger shells lead to much lower rates of fire. Example U.S.Navy: 6" L/47 guns were able to shoot 8-12 times per minute (more under fine conditions), while the U.S.Navy's contemporary 8" L/55 gun fired 3-4 rounds per minute. For comparison: Even 18" guns (Yamato) reached 1.5-2 rpm, German 15" (38 cm) guns reached slightly more than 3 rpm (one salvo every 18 seconds). Fine 5" guns reached 15-22 rpm (practical more like 12-15).
The difference in penetration capability between 6" and 8" wasn't as important given the vast quantities of poorly protected cruisers and the importance of short range night combat. In the end, a 6" armament yielded more firepower than a 8" armament with equal displacement and technology.
8" guns looked more impressive to civilians, though.
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