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mofton

mofton's Tidbit's - British Cruisers in WWII

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Hello All,

Last year I took a look at battleship and carrier 'availability' for the Royal Navy in WWII, indicating that while size matters, frequently on-paper strength is not all that it seems. Those two articles can be found:

and

Some Historic Background

The Royal Navy is sometimes called a 'Battleship Navy' and it absolutely did consider the battleship the ultimate arbiter of force in most of the interwar era. The two major Naval Treaties, Washington in 1922 and London in 1930 were most prescriptive and restrictive on battleships, while the first one also qualitatively limited cruisers (to 10,000t standard and 8in guns - hence 'Treaty Cruiser') the second also imposed quantitative or total limits on numbers and tonnage of Heavy cruisers, and tonnage of light cruisers.

The Royal Navy, with it's far flung colonial empire, while also wanting battleships, destroyers and aircraft carriers (to find and slow the enemy battleships for ours of course) had a major interest in cruisers, and cruiser warfare. Arguably the greatest interest and requirement of any of the major nations. Even during WWI and after the German High Seas Fleet's dispersed formations were wiped out with the Battle of the Falkland Islands (December 1914) and the war generally trended to the RN locking the HSF in the southern North Sea, the British remained interested in cruiser - merchant raiding and protection over wide areas - warfare, building the Renown Class battlecruisers with this in mind, and also investing in a Trade-oriented Hawkins class which were designed in 1915, though not completed until 1919-1925.

After the Washington Naval Treaty, the RN had the fastest build up of heavy cruisers, and after the London Naval Treaty the RN built significantly greater numbers of cruisers than either Japan or the USA, and was leagues ahead of the other minor powers.

image.thumb.png.4d2ca703db028e9b313f20ce50bd2468.png
John Jordan, Warships after Washington - Comparison of Treaty Cruiser Builds
 

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John Jordan, Warships after London, Comparison of Treaty Cruiser Authorizations 1930-1936

Royal Navy planning indicated a varying cruiser requirement - but it was always a high number - with 50-60 ships usually being the bare minimum objective for world-wide ocean control. Reflecting this the RN was practically the only major power to build smaller, producing the only significantly (and intentionally) sub-10,000t post-Treaty Heavy Cruisers (York and Exeter) and accepting 6-gun Arethusa class ships and 5,000-6,000t cruisers when 8,000-10,000 was the norm.

The RN also spent accordingly, from 1930 to 1939 it was cruisers out of all ship types which received the greatest funding:

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D. K Brown, Nelson to Vanguard - Royal Navy Expenditure 1930-1939 by ship type, brackets may indicate number of ships


A total of 92 Royal Navy cruisers served, even if briefly in WWII from the old C-class of WWI (the eldest being the Caledon subclass completed in 1917) to ships coming into commission in 1945, usually after protracted war-time builds. I've repeated similar methodology from last time, though generally sub-divided the results due to sheer numbers. Again availability/not is largely based on http://www.naval-history.net/xGM-aContents.htm

 

'The Rules of the Game'
I have to make certain caveats and assumptions to produce anything usable without going into too much detail - 

  • This is broken down by month, and taken a majority view - if available for more than half the month - available, if available less than half - not
  • 'Available' includes periods after commissioning and initial workup but not necessarily fully worked up
  • Cruisers put into reserve, as dedicated training ships or other uses (often noted) are counted as simply unavailable as they were frequently partially or completely dis-armed, operated with reduced crews and were not combat capable
  • 'Unavailable' includes all periods post damage spent sailing to yards for repair with that damage, and any moves between ports while seriously damaged. This matters because some RN ships took long routes to the US for repair and refit. In this instance I've indicated combat damage in pink, and general wear-and-tear or 'upgrade' refits in white
  • Even if not in 100% operational condition I've tried to let the RN make the call
 

The theatre split is into fairly broad areas, the Mediterranean is fairly self explanatory but for instance Gibraltar, on the Western entrance is as close to the Atlantic as the Med. The grey cells for Home/Arc/Norway include ships based out of Scapa Flow and Iceland. Pink for the Atlantic includes the South and Central North Atlantic west of the UK. The Pacific/Indian ocean split is fairly self explanatory, places including out of Singapore are included in the Far East rather than Pacific. The color key code used below is here:

3RpxF62.png

The Pre-Washington Cruisers

7uhypzo.jpg
IWM Image A 10645 HMS Curacoa, one of eight anti-aircraft conversions of old C-class cruisers. You can see four twin 4in guns, and a pom-pom in B position

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-Availability 'minesweeper' - click to expand, the Forum has shrunk them
 
The pre-Washington cruisers represent all those lain down before the 1922 Treaty, and include 13 of the younger surviving C-class (28 were originally built) of which six started the war as AA conversions, as well as the surviving C, D, E (old 6in-armed) and Hawkins (7.5in, except Effingham) class ships. Of note here my general observations are:
 
  • Early and mid-war most of the non-AA conversions were operated in relatively benign conditions, secondary patrol theaters including the Indian Ocean/East Africa (orange), South/Central Atlantic (Pink) and even until the outbreak of war with Italy in June 1940, the Mediterranean
  • The AA conversions have a more varied history including lots of early work with the home and Mediterranean Fleets - where for instance three would be lost
  • By 1944-1945 these ships are getting phased out, with a big wave post D-Day in 1944, the last in service goes in March 1945 and at that point fifteen ships are not working s front-line warships up, with two more transferred to Poland
  • Combat damage overall was fairly slight with only two ships disabled for long periods (Capetown, Coventry and Delhi) I suspect that is partially because these old, small ships either tended to escape damage altogether or would be sunk outright
  • Refit times are generally short with the exception of the AA conversions of Caledon and Colombo mid-war (several other ships were finishing refits at the outbreak) suggesting a bare minimum of investment just to keep them going - Ceres in particular seems to be an example of getting pretty run into the ground, then discarded
  • These ships have a peak in availability early war, and then general attrition until heavily phased out
  • The most available single ship was the Colombo which seems to have spent a lot of time late war stooging about in the Mediterranean, at a time when it was probably a more passive theater and avoided heavy damage

The Treaty Cruisers

https://media.iwm.org.uk/ciim5/457/614/large_000000.jpg?_ga=2.141616305.2029172442.1606514341-497280767.1548123871
IWM Image A 13456 - HMS Devonshire in 1942 in the Indian Ocean

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These ships represent the core of the inter-war Trade-focused cruisers, ranging from the oldest Kent, London and Norfolk subclasses of the County Heavy cruisers (8in guns) with the smaller York and County, and then 5 British and 3 Australian Leander variants, with the Arethusa class being more Fleet (fight enemy destroyers, protect battleships) focused but lumped in. These ships range from some of the largest (8in guns, >10,000t) to the smallest post-WWI British cruisers, the 5,300t, 6x 6in Arethusa's.
 
The County Class reflect the 10,000t Treaty 'limit' swiftly becoming the standard, rather than the maximum, when you could build as many to the maximum size as you liked. With the London Treaty and on cost grounds the Leander class were an attempt to economize on smaller and hopefully cheaper 7,200t ships without 8in guns.
 
Observations:
 
  • Early war there's a wide range of work in far-flung theaters - at the outbreak in September 1939, only one ship is with the Home Fleet - Aurora, which was Flagship of Rear Admiral (Destroyers)
  • There's generally an early movement out of the Mediterranean when Italy joins the war, when there's a movement inward
  • Throughout there are always ships in the Indian Ocean, even long before Japan joins the war - an indication of all the area German commerce raiders such as Admiral Spee and Admiral Scheer could hold at risk
  • By late 1941 the Counties increasingly diverge with the RN ships focused in the Atlantic/Arctic in partcular, and the RAN ships out in the Pacific
  • These ships mostly stay in frontline service right to the finish, with some getting good length refits for Pacific service - only Kent is put into reserve
  • Combat damage was significant, in particular,
    • Exeter was badly knocked about at the River Plate and had a big combined repair/refit
    • Sussex spent nearly 2 years in repair after being bombed and capsizing in dry dock - I suspect a less valuable ship or one damaged later in the war would be written off instead
    • Leander and Hobart had very long repairs (25 and 18 months) after being struck by single heavy-weight Japanese torpedoes, Kent in contrast needed 9 months for an airborne torpedo, of which 3 were simply getting from Egypt to the UK
    • In contrast to Kent the smaller Arethusa needed 17 months of refit/repair after an airborne torpedo hit, though again 4 months was needed to get from Egypt to the East Coast of the USA
  • Refit times are variable with 4 ships getting pretty considerable refits, and landing main battery guns in several cases at one end, and Kent probably wearing out with only 5 months refit in 3 years at the other
  • These ships have a peak in availability early war, and then general attrition to a low in 1943, rebounding somewhat after that to an average of about 10 ships
  • The most available single ship was HMAS Australia - though data for the Australian ships is coarser, so there may be some missed down time. There are a number of high performers with >50 months (of 72 at war) including Berwick, Cumberland, Devonshire, Shropshire, Orion and Aurora - though only 2 of those ships would suffer major damage

The 12-Gun Light Cruisers

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IWM Image A 19154 - HMS Mauritius, one of the less famous Fiji class

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In the mid 1930's the RN responded to the challenge of the new, powerful 15-gun US Brooklyn and Japanese Mogami class light cruisers by going in that direction themselves. The triple 6in turret allowed a significant increase in firepower over the 8-gun Leander class, leading to the 12-gun, 9,100t Southampton and Gloucester classes and then the 10,550t Edinburgh classes - collectively known as the Town class. The Towns were Britain's newest, most heavily armed and best anti-aircraft equipped ships at the outbreak of war, and although designed as hybrid Trade-Fleet cruisers would see heavy action in the Atlantic, Arctic and Mediterranean.
 
The Fiji class were smaller ships, built to an intended 8,000t limit under the Second London Naval Treaty, though completing over that at 8,550t+. The Fiji's were a case of trying to do too much on too little and several were rebuilt as 9-gun ships by removing X turret, if they survived that late in the war - though several Leander and  County class ships were similarly modified. The Fiji's were lain down in 1938 and started to come into service in the second half of 1940 - the Blitz not being particularly conducive to rapid construction. Due to the rate of attrition the Fiji class ended up maintaining rather than increasing force levels for much of the war. The Swiftsure class was a development of the Fiji and had two ships make it into service just before the end of the war. 
 
6JCs1FT.png
Another way of comparing things - individual blocks per ship, per month showing the general decline (to zero in August 1944) of the Town's with the Fiji's supplementing the dwindling force
 
Observations:
 
  • Early war the Town class are concentrated in the Home Fleet (where ships working up start out) and out in the Far East on show-the-flag Japan deterrence work. Very soon after the outbreak there was a general concentration in home waters.
  • As with the older ships, once Italy joins the war there is a movement to put ships out there, though this is done in stages, and is limited by the near-immediate loss of Southampton, and damaging of Liverpool - Towns have a bad time in the Med
  • Presence in the 'distant' theaters is spotty, with a couple of ships generally in the South Atlantic and Indian Ocean/Far East
  • The Home Fleet remains a priority throughout the war, with a late move to the Pacific - after 1940 deployments to the Mediterranean are frequently on an ad hoc 'big convoy' basis - the Home Fleet acting as the main reserve for operations like Pedestal in August 1942 with two Fiji's and a Town participating and losing 1 ship sunk (Manchester) and the other two torpedoed and damaged
  • These ships mostly stay in frontline service or refit right to the finish - several end the war in refit anticipating the war against Japan lasting into 1946, though there were also manning issues in 1945
  • Combat damage was significant, in particular,
    • Belfast - the longest time spent repairing action damage and upgrading the ship - 35 months after being mined, though problems with the repair effort mean she could have returned sooner
    • Liverpool demonstrates that you don't have to be sunk to be really knocked out, available for just 19 of 72 war months, very promptly torpedoed twice on arrival to the Med - in comparison Gloucester, sunk in May 1941 was available for 20
    • Submarine-inflicted torpedo damage would dog the class, though not outright sink any ships (Edinburgh was torpedoed twice by a U-boat then again by German destroyers) with repair times ranging from 5 months (Fiji) to 13 months (Nigeria)
  • Refit times are fairly consistent - a pattern of short refits early war to add radar - often tacked on to action damage, ships making it to about 3 years old tend to get a long 6+ month 'going to the Pacific' refit
  • These ships have a peak in availability late war - losses peaked in 1941-1942, so new build offsets loss after that. The tranche of Fiji's coming in early 1943 really stabilizes numbers for a while
  • There's a small blip for D-Day but not large compared to other cruiser types
  • The most available single ship was the Sheffield, narrowly followed by the Newcastle, Glasgow, Birmingham and Fiji - though none of them manage 50 months. Sheffield was very much a lucky ship, staying in service despite strenuous service from the Arctic (Barents Sea and North Cape) to Force H (Grog, Bismarck) and a mine off Iceland
 
The Dido Class/Subclass 
jxNwTrz.jpg
IWM Image A 7525, HMS Euraylus leading HMS Galatea
 
3HM5mG3.png
 
The Dido class reflect the need for numbers and for Fleet type cruisers, they are similar in size to the small Arethusa class (5,600t) and their envisaged roles are as 'Fleet' ships in particular. They are meant to fight incoming destroyers, support friendly destroyers and provide AA cover to high value ships like aircraft carriers and battleships. As Fleet units range was less of a consideration so compared to the 10,000 nautical mile at 14kt standard of a York or Leander they could do about 6,000 nautical miles at the same speed. Built right to the edge of a hard limit on size and immediately having war advances - AA guns, radar, degaussing gear etc. added, they suffered from excessive top weight and several ships landed 'Q' mount in partial compensation.
 
The armament of 5.25in guns reflected a new weapon becoming available as they were developed, one which could maim or kill destroyers in relatively few shots, firing an 80lb projectile vs. the 50lb of a 4.7in or US 5in for comparison. The dual-purpose nature of the gun with 80' elevation also meant it could be used in the anti-aircraft role, though it was less successful there thanks to general aiming shortcomings and rate of fire limitations. Shortages of key materials and bottlenecks in gun production were issues getting ships into service, though the first, Bonaventure came in mid-1940, and Naiad probably would have been sooner if not for suffering bomb damage while building.
 
  • As the Dido's commission from 1940 onwards they start life in the Home Fleet working up, before moving to the Mediterranean almost inevitably
  • Mediterranean service sees the greatest concentration, with up to 6 of 7 available ships in August 1942, and heavy involvement in some Malta convoys. Four ships fought at Operation Vigorous, three at Second Sirte and Pedestal had three as well.
  • Presence in the 'distant' theaters is generally low, the ships were ill-suited to trade protection due to size and range (though Bonaventure would engage Hipper protecting an Atlantic convoy)
  • Losses to and damage by submarines are comparatively frequent with Bonaventure and Naiad lost with fairly heavy casualties, and Argonaut and Cleopatra badly damaged by torpedoes
  • These ships mostly stay in frontline service or refit right to the finish - several end the war in refit anticipating the war against Japan lasting into 1946, though there were also manning issues in 1945
  • Combat damage was significant, in particular,
    • Dido - bombed off Crete and out for 6 months, though bomb damage was relatively rare
    • Phoebe was the sole ship of the class hit by an aerial torpedo, surviving with a 7-month repair, though it took 3 months to reach the USA
    • Argonaut (2 hits at extremities, 14 month USA refit), Phoebe (8 month) and Cleopatra (13 month) surviving torpedo damage - though this was sadly not as common as you might think, as small overloaded ships with poor margins of buoyancy and stability and an issue with longitudinal bulheads they were liable to capsize
  • The relative youth of the ships commissioning in 1940-1943, and action damage repairs during which refit additions are made mean refits are fairly infrequent in the war years, only Euryalus enjoyed one, losing 'Q' turret in the process
  • These ships have a peak in availability late war - as new ships outstrip losses, though unlike the 12-gun CL they would suffer outright losses in 1943 and 1944
  • D-Day had a 5 of 9 ship concentration in Home Waters
  • The most available single ship was the Dido herself, although joint 3rd into service she avoided the submarine torpedoes that sank her early sisters Naiad and Bonaventure, and the two instances of damage which reduced Phoebe's availability. Dido spent an impressive 2 months in refit in the last 3 years of the war, though she had other short periods in the yard periodically.

Conclusions

Dep2uFD.png
All-cruiser availability

The Royal Navy needed cruisers, and it needed numbers. World War II inflicted huge losses, both in ships outright lost and those seriously damaged. Damaged ships would frequently face being assigned a low priority, with it being better to get three lightly damaged ships back in the fight in rather than one heavily damaged cripple taking months. Damaged ships also had to compete directly for resources - steel, armor, guns and trained shipwrights, welders, riveters and electricians as newly building ships.

Overall the trend of cruiser availability is downward from 1939, though variable and starting to eke up again in 1945 after the worst fighting is over. Interestingly to me, the low point of 30 ships available in September-November 1943 doesn't coincide with a major battle or disaster - you can see a dip in mid-1941 around Crete, and another in mid-1942 with some heavy action in the Mediterranean, but generally the RN cruiser force was large enough that even losing 3-4 ships damaged in a month makes a small impression. Cumulative losses, damage and refit timing have a big impact.

It's not all grim either, as well as losses a reduction does reflect a force getting rid of a lot of relics - in 1939, 21 ships of 56 in-service cruisers had been lain down before 1920, and 41 ships were pre-1930. By June 1945 the oldest ship in service (Berwick) was lain down in 1924, and just 9 of 44 overall were pre-1930. Of those 44 ships 33 were available, a fairly impressive 75%. Of the oldest ships, 15 of the 26 C-D-E-Hawkins classes were simply in reserve, transferred or even expended as blockships.

Sources:
D. K. Brown - Nelson to Vanguard
John Jordan - Warships after Washington
John Jordan - Warships after London
Navypedia
Naval-History
IWM - Images as captioned
Edited by mofton
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Whilst I think its fair to say that the Fijis attempted too much on too little displacement (post-Treaty growth being a significant factor, such as their torpedo tubes), I think its less fair to say it of the Southamptons and Gloucesters. They suffered from what many other ships of their ilk did, which was the reduction or removal of the growth factor that ships tended to have. Indeed, if Belfast hadn't been bulged, its entirely likely that she too would've lost her X turret.    

Otherwise, fabulous post. 

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The history of the Dido class is somewhat tragic in that the ships really didn't work out all that well.  As cruisers in surface actions their gun power was simply too light, an issue shared by the US Atlanta class.  The Atlanta's had the saving grace of the USN having enough 6" and 8" cruisers for surface actions and they could be relegated to AA fire support.

To make matters worse, many of the Dido class were hastily completed with less than the planned armament.  Several had just 4 5.25" turrets installed on commissioning due to a shortage of these in production.  Two, Scylla and Charybdis, got 4 4.5" turrets instead making them exceptionally weak as gun cruisers.  This in turn caused a problem with fire control as no suitable system for both high angle and low angle fire existed for this gun.  Two different sets of directors were fitted to these ships to allow for both.

They also proved very vulnerable to torpedoing.  To maintain the desired 34 knot top speed, watertight subdivision was sacrificed to allow larger machinery spaces to fit the necessary plant.  This made the class, along with their relatively small size, prone to rapid flooding followed by a loss of power, again due to conscious decisions about machinery and emergency systems.

The 5.25" compromise on this class proved exactly that in combat actions.  The gun was less effective for AA fire and was less effective in surface actions too.  It was a compromise that compromised the role of the ship.

Three of the class were sunk by torpedoes (Naiad, Bonaventure, Hermione), from by submarines, and one by torpedo boat (Charybdis), each by a single torpedo hit.  A fifth was sunk off Anzio by bombing (Spartan).  In this case, a single hit by an Hs 293 guided missile / bomb.

The postwar Minotaur class was designed with an eye to fixing all the major issues that plagued the Dido's during the war.

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6 hours ago, mr3awsome said:

Whilst I think its fair to say that the Fijis attempted too much on too little displacement (post-Treaty growth being a significant factor, such as their torpedo tubes), I think its less fair to say it of the Southamptons and Gloucesters. They suffered from what many other ships of their ilk did, which was the reduction or removal of the growth factor that ships tended to have. Indeed, if Belfast hadn't been bulged, its entirely likely that she too would've lost her X turret.    

Otherwise, fabulous post. 

Maybe I'm misreading the Fiji's and 9,100t Southampton/Gloucester class. I'm not sure on Belfast keeping or losing X without the bulging, she could have lost a pair of 4in's as she did anyway.

I guess part of my thinking was that the roughly equivalent Cleveland's kept (unless missile converted) all their guns, but were 11,000t ships with lots of bells and whistles like the 6x2 5in. The surviving Brooklyn's started at 10,000-10,600 and got bulged which is probably more than compensation for the 5th triple turret - none of them landed one.

Maybe given the landing X was a feature not just of the Fiji's and smaller-Town's but also of the Leander's and some of the County Class - which were not over-gunned for their size - it's not a fair statement. I'll update that section.

 

2 hours ago, Murotsu said:

To make matters worse, many of the Dido class were hastily completed with less than the planned armament.  Several had just 4 5.25" turrets installed on commissioning due to a shortage of these in production.  Two, Scylla and Charybdis, got 4 4.5" turrets instead making them exceptionally weak as gun cruisers.  This in turn caused a problem with fire control as no suitable system for both high angle and low angle fire existed for this gun.  Two different sets of directors were fitted to these ships to allow for both. 

It's not so much haste as bottlenecks, Dido for instance was about 3 years from keel to completion - that's about the same or even a bit slower than pre-war 6in cruisers which were usually about 2.5-3 years. The problem was the relatively slow and difficult to construct 5.25in guns, which like the 4.7in/50 seem to have needed a lot of laborious work, while the more basic 6in/50 seem to have had a well established production regime with fewer hangups for the Town's and Fiji's.

It's definitely a detriment to need separate fire control systems, and a further one that HACS Mk. IV* simply isn't as good as the US's superlative Mk. 37 system. 

Overall, I think the potential weaknesses as gun cruisers for surface actions weren't much borne out. In short:

  • Mostly they just didn't fight gun actions with other ships due to the nature of the war and how they were employed - which is not dissimilar from the Atlanta's
  • The only surface action the 4.5in armed ships got into was with German Type 39 torpedo boats, for which a 55lb 4.5in round was more than sufficient - had the tactical picture not been a disaster
  • There is a direct comparison between 3 Dido's and a British 6in gun cruiser at 2nd Sirte, in the bad conditions the 6in gun cruiser (Penelope) achieved no more hits than the 5.25in (i.e. zero), and given they were shooting at a battleship the damage is unlikely to be dissimilar even if they did hit - at the same time the Italian 6in cruisers achieved almost nothing (1 hit), and the 8in a handful of straddles, it's hard to say the 5.25in was doing worse than equivalent 6in's.
  • When employed anti-destroyer or smaller as intended the 5.25in seems to have done fine, especially at night and at close range with Force K (3rd) against the Italians

The gun definitely underperformed overall, but the sustained 8 RPM is a decent advance on 6in cruisers doing typically about 5-6 RPM. The burst capacity against short lived air attacks was probably reasonable, and the comparison should be to most British cruisers which would at best get 2x2 4in guns onto an incoming air attack, and then not have as good arcs as the Dido's.

Completing with 4 instead of 5 turrets was ironically probably sensible given older ships often lost a turret during refits, and the entire larger and later Bellona subclass had only 4 as designed and completed.

1 hour ago, Murotsu said:

They also proved very vulnerable to torpedoing.  To maintain the desired 34 knot top speed, watertight subdivision was sacrificed to allow larger machinery spaces to fit the necessary plant.  This made the class, along with their relatively small size, prone to rapid flooding followed by a loss of power, again due to conscious decisions about machinery and emergency systems.

 

2 hours ago, Murotsu said:

Three of the class were sunk by torpedoes (Naiad, Bonaventure, Hermione), from by submarines, and one by torpedo boat (Charybdis), each by a single torpedo hit.  A fifth was sunk off Anzio by bombing (Spartan).  In this case, a single hit by an Hs 293 guided missile / bomb. 

I definitely agree that the small size and lack of diesel generators were a problem and shortcoming, sadly not limited to the Dido's - but emblematic of the RN having an aversion to diesel emergency generators overall, much to its discomfort.

The other key issue I've seen per D. K. Brown and other sources were the longitudinal bulkheads of the 'wing spaces' abreast the after boiler room. Flooding one of them would be limited to the outer part of the ship, imparting a much stronger lever arm, which in combination with other flooding could be extremely dangerous.

I've not seen anything about a desired 34kt top speed, the end design was based on Preliminary 'P' which was only 30.75kt, then scaled up in size and speed to a pretty typical British 32.2kt on 62,000 SHP,  pretty much the same as the 32.3kt of the 64,000 SHP Arethusa's of a similar, though slightly smaller size. The British did spend length to at least give a 'unit' layout to the machinery, and I don't think the sizes were any smaller than normal as a proportion of the length. If you have a source on a 34kt speed objective I'd be interested to know more there. The problem from everything I've read is simply that the class are small, with small machinery spaces, a low margin of stability, flooding vulnerability and torpedoes would damage:

A typical Second World War torpedo would make a hole some 35ft long and 15ft high, rendering bulkheads non-watertight over twice that length. A torpedo would flood at least two compartments and probably three along the length.

Brown, David K.. Nelson to Vanguard: Warship Design and Development, 1923–1945 (Chatham's Distinguished Design) (p. 408). Pen & Sword Books. Kindle Edition.

 

IDGjxYM.jpgInfor1Gbd8jh.jpg
Information/images from D. K. Brown's Nelson to Vanguard
 
Of the four cases of Dido losses to torpedo damage it would seem that at least two of them, Charybdis and Bonaventure were struck approximately amidships, in the most vulnerable areas by two torpedoes. Two separated torpedoes into the machinery spaces is arguably not survivable for many cruisers, especially a small <6,000t standard one. The Hermione might have been two torpedoes landing in the same rough area, and only Naiad seems to be a definite single torpedo, probably in about the worst possible place, definitely and immediately flooding the forward two spaces and then subsequent flooding and the flooding through bulkhead collapse of the aft engine room, with 3 of 4 of the main machinery spaces flooding she was going to be in dire straits.
 
I can't think of any small cruisers that took two torpedoes roughly amidships and kept floating.

Here's some more information on each sinking, the images are from 'HM Ships Damaged or Sunk by Enemy Action' an official British Admiralty document circa 1952. It definitely supports issues with the compartment access, lack of diesel generation and rapid list after damage near the wing spaces (20' on Charybdis after the first hit flooded the dynamo wing space and a boiler room).

 

Loss of HMS Naiad

At 2005 torpedoes were seen passing ahead and astern of Naiad but a third struck amidships at Frame 99, the bulkhead separating the Forward Engine Room and ‘B’ Boiler Room aft. An immediate list of ten degrees to starboard increased to twenty degrees as both compartments flooded. Orders were passed to seal off all internal doors and the flooding was temporarily contained while efforts were made to extricate those inside. Here the design faults of the Dido class began to tell, for though men were saved through manholes illegally cut into the top of these and other compartments by the Senior Engineer, Lt (E) Louis Le Bailly, it had not been possible to make similar provision for other machinery spaces. This meant that trapped men either drowned or were forced to open doors onto adjoining passages, thereby compromising the watertight integrity of the entire ship. Cdr Roy Dowling RAN was later to testify that all accessible watertight doors were closed as a matter of course, but subsequent orders to seal internal doors were not thought to have reached both ends of the ship and at least one was unclipped to permit escape. A further design omission was the lack of an emergency diesel generator. With the four dynamos either destroyed or lacking steam power, efforts at damage control were therefore hampered by a complete failure of electrical power together with a breakdown in Naiad’s telephone system as she continued her list to starboard. Naiad’s fate was sealed by the flooding of one or both of the wing spaces abreast ‘B’ Boiler Room, water spreading along the ship via the cable passage. Together with the inrush of water from the speed of the ship, this caused the collapse of the bulkhead separating that space and the After Engine Room, an event that brought Naiad onto her beam ends at around 2030, twenty-five minutes after the attack.

Daniel Morgan, Bruce Taylor. U-Boat Attack Logs (Kindle Locations 13314-13328). Seaforth Publishing.

Naiad was lost with 77 dead, 592 survivors. I think a decent survival rate. I think the triple-whammy of flooding and general failure of watertight integrity are an issue here.

 

Loss of HMS Hermione

Both the After Engine Room and ‘B’ Boiler Room flooded immediately, the stern settled rapidly and the quarterdeck was soon awash. The blast wrecked an armoured bulkhead door and both passage doors on the lower deck allowing water to flow along the starboard side as far as the stokers’ mess deck, assisted by the flooding of ventilation trunking as the ship capsized.

Admiral Harwood was quick to point out the similarities between the loss of Hermione and her sister Naiad (54) ‘consequent upon the effects of one, repeat one torpedo explosion in the machinery spaces, and it is felt that certain features in the design of this class need re-consideration’. Various measures including the strengthening of bulkheads, the reduction in the number of doors in transverse bulkheads, and the introduction of additional bulkheads between the lower and upper decks were proposed. Though expert opinion was and remains unanimous that the Dido-class cruisers were much too easily sunk, with hindsight it is by no means certain that Hermione was the victim of only one torpedo. While Reschke’s implication of three hits may be taking things too far, Dido herself observed two distinct flashes from Hermione at 0127. Certainly, the damage sustained by Hermione and the speed of her sinking would be consistent with a second hit in the same vicinity as the first.

Daniel Morgan, Bruce Taylor. U-Boat Attack Logs (Kindle Locations 15435-15438). Seaforth Publishing.

Hermione went down with 88 of her crew, and probably about 500 survivors. Pretty similar to Naiad and reflecting at least some time to escape, with a lot of casualties in the immediately flooded sections. Reschke is the U-boat commander responsible.

 

Loss of Charybdis

The first torpedo had hit her port side, flooding No.2 dynamo room and "B" boiler room and putting the after unit out of action. The Executive Officer, Commander Oddie, who was on the bridge at the time, went aft to take charge; by the time he reached the upper deck, the ship was listing about 20°. As he proceeded aft, the second torpedo struck the ship at about 135 station, and caused very heavy damage, displacing the after director and flooding the after engine room; all electric light failed and in about five minutes the list had increased to some 50°. Communication with the bridge had failed and Commander Oddie, seeing there was no hope of saving the ship, ordered the Carley rafts to be manned. Shortly afterwards, while climbing along the starboard side, in an endeavour to reach the bridge, he fell into the sea, and in a few minutes saw the ship suddenly take an angle by the stern till she was nearly vertical. She remained in this position for about half an hour with one third of her length out of water, and then sank." This was at approximately 0230. https://www.naval-history.net/WW2Ships-CharybdisAsr.htm

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538 killed and 150 survivors. This is pretty clearly a two hit scenario, with the first probably survivable (one big and a wing) and then the second compromising possibly another two. I can't imagine the horror of those trapped inside a near-vertical ship for 30 minutes, struggling to escape.

 

Loss of Bonaventure

At 2:37 on March 31, 1941, she sighted a large escorted ship moving at an estimated speed of 10 knots. At 2:44 she launched three torpedoes at the target and remained on the surface to observe the results. Two torpedoes hit the ship in the middle, and Arillo, in the dark, assumed he had torpedoed a large tanker. The ship hit was actually British light cruiser HMS Bonaventure escorting convoy GA8 from Greece to Alexandria along with destroyers HMAS Stuart, HMS Griffin and HMS Hereward. Hit in both of her engine rooms Bonaventure quickly sank within five or six minutes in the position 33°20′N 26°35′E with 139 casualties and 310 survivors. (Wikipedia)

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139 killed, unknown survivors (310 is cited but seems unlikely given nominal complement of about 500). Not the best description. A hit to the after end of the forward engine room would certainly flood that and a wing/turbine compartment, then one into the after engine room might take that and further aft compartments out. None of the other ships hit by a single torpedo capsized in as little as 5-6 minutes even if 30 is far sooner than you'd hope for.

Loss of Spartan

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65 killed, 523 survivors. This seems like a combination of initial flooding and secondary explosions and fires. Two compartments including the wing flooding and a rapid list causing secondary flooding fairly high in the ship (presumably through splinter damage). Major secondary fires were a huge issue, then even more loss of buoyancy thanks to flooding magazines as a preventative, electrical power an issue due to switchboard damage is a common theme, even with steam for the dynamos.

The HS 293 only had a moderate sized warhead at 600lb, but probably had quite a lot of attached mass all things considered. There are some odd veiled mentions of strange things happening, but I think sometimes even with the best will in the world initial and secondary damage gets away, and the rapid initial list which is unusual for most bomb damage likely didn't help.

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17 hours ago, mofton said:

Maybe I'm misreading the Fiji's and 9,100t Southampton/Gloucester class. I'm not sure on Belfast keeping or losing X without the bulging, she could have lost a pair of 4in's as she did anyway.

I guess part of my thinking was that the roughly equivalent Cleveland's kept (unless missile converted) all their guns, but were 11,000t ships with lots of bells and whistles like the 6x2 5in. The surviving Brooklyn's started at 10,000-10,600 and got bulged which is probably more than compensation for the 5th triple turret - none of them landed one.

Maybe given the landing X was a feature not just of the Fiji's and smaller-Town's but also of the Leander's and some of the County Class - which were not over-gunned for their size - it's not a fair statement. I'll update that section.

Or she would've lost the 4" twins as well.    

The Clevelands did lose some things, but it was mainly limited to things like boats and one of the catapults. Part of that is probably thanks to being larger in all three dimensions, but there was, I seem to recall, a willingness to accept less strenuous values than what the Admiralty wanted. 

Indeed, concerns with stability were what led to more drastic changes in the Fargos. 

 

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With Spartan the hit would have been similar to a modern anti-ship missile.  The Hs 293 travelled at about 500 mph and that would have been the speed of impact.  The bomb had delayed fuzing normally so it would have detonated deep in the ship.  Any remaining rocket motor fuel the missile had would have caused additional fires around the point of impact.  High Test Peroxide (HTP) will spontaneously combust with any oil or grease it comes in contact with.  Once such a fire is started it will feed on any remaining oil or grease present as a normal oil fire would.

On the whole, an Hs 293 hit would be very much akin to one by an Exocet (364 lbs. warhead) or Harpoon (488 lbs.).

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ufKpIQb.jpg
So as a bit of a glutton for punishment I thought I'd look at the Mediterranean - one of the most costly theaters for British cruisers - from June 1940 to September 1943, the war with Italy.
 
Total numbers fluctuated wildly, the highest numbers corresponding with the Invasion of North Africa (Operation Torch) in November 1942. The low of 3 ships in September 1942 shows the aftermath of the heavy losses of Operation Pedestal (a Malta convoy) which had Kenya damaged as well as the Cairo and Manchester.
 
The British Home Fleet acted as a 'strategic reserve' of ships hence you see blips of Fiji and Town class cruisers entering the Med around key periods, in particular convoys.
 
Some thoughts -
  • The heavy cruisers barely see any action in the theater, largely avoiding it to better exploit their range (and mitigate some AA weakness) in other areas
  • The Town class are more active early war, but then generally decline in relevance excepting reinforcement 'blips' most operate from Alexandria, but Sheffield operates with Force H out of Gibraltar until mid-1941
  • The modern twin-turret 6in gun cruisers (Leander, Amphion and Arethusa) classes go through 1940 and 1941 strong, but are hit hard with losses in late 1941, leaving just Penelope until she is put out of action by bombing in Malta. From Spring 1942 the central Mediterranean is an Axis lake.
  • Dido's really come to dominate the vestigal force, mostly based out of Alexandria in 1942, some ships do come in as temporary reinforcements from Gibraltar/the UK for surge periods
  • Cool 1

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