Rn vs IJN

[Shortround6]

This is all quite interesting, (sincerely) but the point of the thread was really just to compare and contrast the naval resources, fleets and fighting machines (in the air, on the water, under the water etc.) of the two nations. And I think it's already pretty clear: The IJN was superior, even if you brought most of the RN over to contend with them. Numbers are really the main advantage the British have. Radar and functional torpedoes will help, superior cryptography will help more, but not enough to overcome the clear and blatant inferiority in aircraft, and (the more arguable but I think also pretty clear) disadvantage in warships.

And the whole point of that is just to show that the Japanese were not, in fact behind technologically or militarily. In 1941 they probably had the best, (if not the largest) navy in the world. They did gradually fall behind and stumbled in some of their weapon development in 1943, but they were still quite formidable on the world stage even into 1944, probably until after the Battle of Leyte Gulf. Only the USN could stand up to them (with the help of USAAF and RAAF air assets, and RN and RAN as well). Victory over the Japanese was neither easy nor (in my opinion) a foregone conclusion. Yes they looked weak in 1945. They had lost the war by then. Most of their fighting age men, cities, and all of their major war machines had been annihilated.

They did not look so weak in 1941, 1942, or even 1943. To the contrary, they looked terrifying.

As for scenarios, it does seem like oil in Brunei and / or Dutch East Indies would be pretty tempting. I think that was the whole point behind their attempt to push into Russian Siberia prior to Kalninin Gol (oil, I mean). Rubber in Indochina looks pretty tempting too. Bauxite (aluminum ore), copper and iron etc. in Malaya as well.

well, I am just trying to set a plausible scenario. Then we can discuses plausible forces involved and discuss actual technical factors which might affect combat.
My Scenario actually gives the British more combat experiences than the Germans stay home go to the beer garden scenario

For the Navies the carriers have been done to death and yes the RN carriers are well behind in general but no, the RN is not going to go to war in Dec 1941 with Skuas and Rocs.

For battleships?
from Wiki so corrections welcome. for the Musashi.
"Musashi was commissioned at Nagasaki on 5 August 1942, and assigned to the 1st Battleship Division, together with Yamato, Nagato and Mutsu.[22] Beginning five days later, the ship conducted machinery and aircraft-handling trials near Hashirajima. Her secondary armament of twelve 127 mm guns, 12 triple 25 mm gun mounts, and four 13.2 mm (0.52 in) anti-aircraft machine guns was fitted 3–28 September 1942 at Kure, as well as a Type 21 radar. The ship was working up for the rest of the year."
So basically the Musashi is out of play for all of 1942.
the Yamato isn't commissioned until Dec 16th 1941. She is not assigned duty in the fleet in actual operations until May of 1942.

This leaves 10 BB,
The Nagatos, two ships
25kts, 8 X16in guns. 18 X 5.5in guns low angle, 8 X 5in guns AA and some light AA

The Ise class, two ships
24-25kts, 12 X14in guns. 16 X 5.5in guns low angle, 8 X 5in guns AA and some light AA

The Fuso class, two ships
24-25kts, 12 X14in guns. 14 X 5.5in guns low angle, 8 X 5in guns AA and some light AA

the Kongos 4 ships
24-25kts, 12 X14in guns. 14 X 6in guns low angle, 8 X 5in guns AA and some light AA

A few notes, the Japanese AA was not very good. The 5in was slow to train and was medium in rate of fire.
The 25mm guns sucked and the 13mm guns sucked.

for the British you have
2 Nelsons state of repair?
3 KGVs and two building
Hood sunk.
4 or 5 QE2s (Barham?)
Renown and Repulse
4 of the R's (Royal Oak sunk)

British AA is all over the place. from pretty good (Renown and QE/Valiant) OK (ships with 5.25in guns) to poor (most of the ships with 8 X 4in guns) to bad (Repulse and the Nelsons)
although the light AA wasn't as bad as the Japanese and got better.

Now how many do you need to ride herd on the two sisters and the Italians, this last can be variable depending on the state of Italy Still a combatant or sued for peace?) and the state of French Navy/Vichy.
With the Italians out of NA at the least and Algiers and Tunisia in allied hands (or at least not axis) Getting ships through the Med has different degrees of difficulty.

Cruisers in part II

 

[Shortround6]

Cruisers.
Change by going list by age by age.

Tenryu class 2 ships 1918 about 4000 tons. 33kts
four X 5.5in guns, four X 25mm guns, 2 X 13.2mm machine guns, six X 21 in tubes.

early photo, 2nd line by 1941.

Kuma class 5 ships 1918 about 5500 tons. 36kts 1919-1921.
7 X 5.5in guns, 4 X 25mm AA guns, 2 X 13.2mm machine guns, eight X 21 in tubes.

model but many photos of the ships have awnings or bad shadows. Note that the torpedoes are two pairs of twin tubes on each side.
The torpedo cruisers have been mentioned already and as the war went on catapults and even one or two main guns were sacrificed for more 25mm guns.

Nagara class 6 ships 1921-23 about 5570 tons. 36kts 1919-1921.
7 X 5.5in guns, 2 X 3in AA guns (?) 2 X 13.2mm machine guns, eight X 24 in tubes.
Visual almost identical to the Kuma class,

Sendai-class 3 ships 1924-25 about 5200 tons. 35.25kts
7 X 5.5in guns, 4 X 25mm AA guns (?) 2 X 13.2mm machine guns, eight X 24 in tubes.
Pretty much repeats of the previous two classes.

Yubari class 1 ship. 1923 about 3560tons 35kts.
6 X 5.5in guns, 1 X 3in AA gun 2 X 13.2mm machine guns (?), Six X 24 in tubes.

guns are one single gun with a twin above and X turret is a twin with a single in Y mount,
The triple tubes are center line.

The next Japanese actual light cruiser is the Agano class of Nov 1942 so I will switch to the Heavies now.
Please note that ANY reference to a Japanese light cruiser before Nov/Dec of 1942 refers to one of the 17 above cruisers.

The British had 21 pre-1921 cruisers afloat in late 1941, 3 C class and one d and one Hawkins having been sunk by that time, number damaged?

However British also had 8 Leander/Perths, 4 Arethusa, 6 Dido's for small 6 in Cruisers available (or at least floating) in late 1941.

8in gun cruisers next.

 

[Wild_Bill_Kelso]

Yubari looks pretty cool.... it's funny how some of even the CAs look pretty .... goofy. But some of them look cool.

 

[Shortround6]

Heavy Cruisers
the work horses of the Japanese fleet.

Furutaka and Aoba classes 4 ships
1926-27 about 8700-9100 tons. 33kts
6 X 8in guns, 4 X 4,7in AA, 8 X 25mm AA, 4 X 13.2mm AA, eight X 24in torpedo tubes. 1 catapult and 2 aircraft.

Another model but it has the best detail

Myōkō-class cruisers 4 ships
1928-29 about 12,280-13,000 tons. 33kts (?)
10 X 8in guns, 8 X 5in AA, 8 X 25mm AA, 4 X 13.2mm AA, sixteen X 24in torpedo tubes. 2 catapult and 3 aircraft.

Yes these were probably the most powerful heavy Cruisers in the World, actual technical achievement is more questionable
as the Japanese lied like hell about the displacement, easy to be more powerful when you make your cruisers 20-30% heavier than the other navies.

The Takao Class 4 ships
1932 about 12,600-13,400 tons. 33kts (?)
10 X 8in guns, 8 X 5in AA, 8 X 25mm AA, 4 X 13.2mm AA, sixteen X 24in torpedo tubes. 2 catapult and 3 aircraft.

Differences in superstructure and funnels but otherwise about the same.

Mogami class. 4 ships.
1935-37 about 12,400. 35kts ???
as built 15 X 6.1in guns, 8 X 5in AA guns, 2 X 2pdr, twelve X 24 in tubes 3 aircraft
when war broke out.
10 X 8in guns, 8 X 5in AA, 8 X 25mm AA, 4 X 13.2mm AA, twelve X 24in torpedo tubes. 2 catapult and 3 aircraft.

the Tone class 2 ships
1938-39 about 11,215 tons 35kts
8 X 8in guns, 8 X 5in AA, 1 X 25mm AA, 4 X, twelve X 24in torpedo tubes. 2 catapult and 6 aircraft.(?)

the famous cruiser carriers, they may not have got the full number of aircraft.
The Japanese never laid down another 8in cruiser or indeed any cruiser of over 8100 tons.

16 heavy cruisers

Japanese cruisers end with the Agano class of 4 ships and the single Oyodo.

Agano class
1942-44 about 6650 tons 35kts
6 X 6 in guns, 4 X 3in AA, 6 X 25mm AA, 4 X, 4 X 13.2mm AA guns, eight X 24in torpedo tubes. 1 catapult and 2 aircraft.(?) and a few depth charges.

torpedoes are on the centerline. One paired 3in gun just forward of the funnel on each side, later in the war the amount of 25mm guns grew considerably.

Note that the British Arethusa class had two twin 4in AA on each side and quad pom-pom on each side in 1940-41 and that was not enough.

We end the Japanese cruisers with the Oyodo of 1943 the eight planned additional ships were never laid down.
8150 tons 35kts
6 X 6.1 in guns, 8 X 3.9in AA, 12 X 25mm AA, 4 X, 1 catapult and 2 aircraft.(?) or six aircraft planned?

No mention of torpedo tubes but using your scout cruiser float plane carriers for torpedo attack was probably not the best idea anyway.

The British had built 13 eight gun 8n cruisers and two 6 gun cruisers, Only York had been sunk by Dec 1941 and that was in Crete evacuation.
The British never built another 8in cruiser, They did build 10 of the 12 gun 6in cruisers of the Southampton through Edinburgh classes and had completed 5 of the 11 Fiji's by the end of 1941 (although not all in commission? )
Crete saw a number of these cruisers sunk.

It may depend on how we view the British big 6in gun cruisers, At 8,500 to 10,500 tons they have the size of some heavy cruisers.
either the British have a bit of a deficient in heavy cruisers and out number the Japanese by about 2 to 1 in light cruisers (and a Southampton vs Kumo match up is not going to go well for the Japanese if they don't get a torpedo hit) or the British do have a numerical advantage in large cruisers even if not 8in ones.

 

[WARSPITER]

The Kongo class were actually Battlecruisers which shows with the lower armour.
The 14" guns used by the IJN were not the more modern type of the KGV class
leaving them outgunned in that respect.

 

[EwenS]

The British had 21 pre-1921 cruisers afloat in late 1941, 3 C class and one d and one Hawkins having been sunk by that time, number damaged?

However British also had 8 Leander/Perths, 4 Arethusa, 6 Dido's for small 6 in Cruisers available (or at least floating) in late 1941.

But of those 21 old cruisers 4 were AA cruisers armed only with 4" guns and lighter AA (Coventry, Curacao, Carlisle & Cairo) while Cardiff had been a Gunnery Training Ship since being withdrawn from the front line in Oct 1940.

And Delhi was being converted to an AA cruiser in the USA with a main armament of 5x5"/38. She didn't return to service until May 1942 after further work in Britain plus trials etc.

Frobisher didn't rejoin the fleet until Jan 1942, having been rearming since the outbreak of WW2. She had a low priority so the work took a long time.

Nov/Dec 1941 was costly for the RN/RAN historically. Ark Royal, Barham, Sydney, Neptune & Galatea all sunk. QE & Valiant put out of action at Alexandria.

And of the 6x5.25" armed Didos, Cleopatra only completed in Dec 1941 (as did the 4.5" armed Charybdis) but Phoebe was in the USA undergoing major repairs for torpedo damage suffered in Aug and didn't return to the fleet until July 1942.

Edit - and don't forget the old HMAS Adelaide.

 

[EwenS]

The British had built 13 eight gun 8n cruisers and two 6 gun cruisers, Only York had been sunk by Dec 1941 and that was in Crete evacuation.
The British never built another 8in cruiser, They did build 10 of the 12 gun 6in cruisers of the Southampton through Edinburgh classes and had completed 5 of the 11 Fiji's by the end of 1941 (although not all in commission? )
Crete saw a number of these cruisers sunk.

It may depend on how we view the British big 6in gun cruisers, At 8,500 to 10,500 tons they have the size of some heavy cruisers.
either the British have a bit of a deficient in heavy cruisers and out number the Japanese by about 2 to 1 in light cruisers (and a Southampton vs Kumo match up is not going to go well for the Japanese if they don't get a torpedo hit) or the British do have a numerical advantage in large cruisers even if not 8in ones.

Of the 13 County class, Sussex was under long term repair from Sept 1940 to Aug 1942 having been bombed during the blitz on Glasgow.

While Britain never built another 8" cruiser after completing the Exeter in 1931, they did not give up on the idea. There were plans for a new "Admiral" class with 9x8" (3x3) from about 1938/39 to Oct 1942, but WW2 meant the resources could not be spared to build them. Courtesy of Churchill, in 1939/40 there was even a short lived suggestion (I wouldn't even call it a serious proposal, let alone a plan, because it was shot down so quickly by the Admirals!) for a 9.2" armed cruiser.

Of the 10 Towns (Southampton - Edinburgh classes), 2 had been sunk by late 1941 and Belfast was under long term repair between Nov 1939 and Oct 1942 having been mined. Manchester was under repair July 1941 to May 1942 first in the USA then Britain, with torpedo damage.

Fiji class 5 completed by end of 1941 with 1 lost.

Then there were routine refits and lesser repairs for weather and / or action damage to figure into the numbers equation. Mauritius (Fiji class) for example was in refit at Singapore from Nov 1941 but on outbreak of war with Japan was immediately undocked and sent home only to complete the refit in April 1942.

 

[mack8]

Just to add a few things, re the scenario for IJN vs RN, mine is for UK and France NOT to declare war in Sept 1939, and then Hitler attacks USSR in 1940 (and gets bogged down there as OTL). France and UK then warily watch from the sidelines (and presumably send aid to USSR), while continuing their rearmament programs. So imo this is as close to a one on one IJN v RN fight you can get, France's Navy is intact but presumably they will mostly keep an eye on the germans and italians, together with a portion of RN (as detailed in one of EwenS's previous posts). France might send a token force in the Pacific, some cruisers, DDs, subs etc, and some troops and planes in their colonies, but it will probably have a limited effect on our IJN vs RN match.

Re IJN cruisers, the japanese actually had laid down 2 Ibuki class cruisers (but 1, No.301 Kurama was immediately stopped and dismantled after Midway, the other, Ibuki was converted to CVL, but unfinished as work stopped in 1945).

Also there was the Niyodo, sistership to Oyodo, but this was cancelled as well before being laid down. (not quite sure if to make room for the Ibukis or due to Midway)

Wild Bill Kelso, re the Komandorski battle note that it was the IJN who had 2 CA and 2 CL, the USN had only 1 of each.

Anyway, nice to see all these ship details in one place. Are you guys going to do british cruisers and destroyers too?

 

[Geoffrey Sinclair]

IJN end November 1941, nominal strength
10 battleships, 6 Fleet, 3 light fleet, 1 escort carrier, 18 heavy, 22 light (including training types) cruisers, 68 modern and 55 older destroyers, 4 escorts, 64 submarines.

RN end November 1941, nominal strength (ignores "free" ships from other navies fighting Germany and Italy)
15 battleships, 6 Fleet, 2 light fleet, 2 escort carrier, 16 heavy, 48 light (including AA types) cruisers, 86 modern and 69 older destroyers (plus 48 ex USN destroyers), 41 destroyer escorts, 218 escorts (including 10 ex US), 59 submarines.

RN losses September 1939 to November 1941 inclusive,
3 battleships, 3 Fleet carrier, 1 heavy, 10 light (including AA types) cruisers, 47 modern and 10 older destroyers (plus 2 ex USN destroyers), 1 destroyer escort, 13 escorts, 35 submarines.

 

[Shortround6]

I would like to thank EwinS, Mack8 and Geoffrey Sinclair for their contributions and corrections to the British and IJN orders of battle. Just trying to figure out the status of the Japanese ships (latest modifications until Dec 1941) was a bit of work. Somebody may have a bit different information. That is fine.

Trying to sort out the Japanese destroyers and while the modern ones look easy (at first glance) the older ones get a bit tricky, there are a number that go back to 1916-17 and were a nominal 850 tons standard and much like the British Admiralty S class (and the old Skate which was an R) were often used for other things and would up as patrol boats or tenders.
Some were 1345-1400 tons.

As built.
Again, thank you gentlemen.

 

[Clayton Magnet]

Am I mistaken in believing that the RN went to war as the only signatory that took the Washington Naval Treaty seriously (sort of)? And the resultant fleet available in 1939-41 reflected as such?

 

[WARSPITER]

The treaty ended in 1936. Up till then it had been adhered to by Japan, Britain, and the USA.

By the end of 1936 Japan wanted parity with the other navies as they were limited to 9 capital
ships whereas the other two navies were allowed 15 each. Japan opted out of attending another conference
and away everybody went again.

 

[EwenS]

Am I mistaken in believing that the RN went to war as the only signatory that took the Washington Naval Treaty seriously (sort of)? And the resultant fleet available in 1939-41 reflected as such?

The 1922 Washington Treaty and the 1930 London Treaty expired on 31 Dec 1936. So there was a flurry of activity in 1935/36 to design ships to use up available tonnages before its expiry. So ships like the carrier USS Wasp and the 2 British Edinburgh class cruisers come to mind.

The Japanese, in compliance with the 1922 Treaty, gave notice in Dec 1934 that they would be withdrawing from the 1922 Treaty. It was however hoped that they might be persuaded to rejoin, or at least not build ships hugely different from the limits set out in the 1936 London Treaty. Nowhere is that clearer than in Article IV(2) of the 1936 Treaty:-

"No capital ship shall carry a gun with a calibre exceeding 14 in. (356 mm.); provided however that if any of the Parties to the Treaty for the Limitation of Naval Armament signed at Washington on 6 February 1922, should fail to enter into an agreement to conform to this provision prior to the date of the coming into force of the present Treaty, but in any case not later than 1 April 1937, the maximum calibre of gun carried by capital ships shall be 16 in. (406 mm.)."

Japan didn't sign up so the gun limit reverted to 16" on 1 April 1937.

The problem for Britain was that it needed to start its capital ship building programme as soon as possible after 31 Dec 1936 and couldn't afford to wait for a Japanese decision in the first 3 months 1937 to design a new capital ship. KGV and POW were laid down on 1 Jan 1937 after a lengthy design period. At one point in late 1935, for the space of only a few weeks, the Admiralty's choice was a battleship armed with 9x15" (3x3). Then came the 1936 Treaty.

The US on the other hand felt it could wait a bit longer, allowing the North Carolina design to be changed to incorporate the 16" gun in time to have the ship laid down in Oct 1937.

I think most signatory nations tried to comply with the 1922 Treaty, or at least no one set out to disregard them completely. One of the problems was that ship design was not an exact science. Until Washington, no one had tried to build a ship to a theoretical figure of "standard displacement" tonnage before. Everyone, including Britain, played the "game" to a greater or lesser extent (e.g. including a load of ammo in magazines capable of holding more in the event of war).

So you get the problems of the 10,000 ton Treaty cruisers. The Japanese tried to squeeze a quart into a pint pot, and found their ships had stability problems leading to weight increases to fix them. So the Myokos came out about 11,000 tons. On the other hand, despite starting later and being able to see what other nations had achieved, the US Pensacolas came out significantly underweight.

Germany of course was not a signatory to the Washington Treaty. What it could or could not do was governed by the Versailles Treaty of 1919. Hence it was able to build the Deutschlands as replacements for its old Battleships that needed replaced. Germany's next constraint was the Anglo German Naval Agreement of 1935 that allowed it to build up to approx 35% of the RN tonnage.

 

[Clayton Magnet]

The 1922 Washington Treaty and the 1930 London Treaty expired on 31 Dec 1936. So there was a flurry of activity in 1935/36 to design ships to use up available tonnages before its expiry. So ships like the carrier USS Wasp and the 2 British Edinburgh class cruisers come to mind.

The Japanese, in compliance with the 1922 Treaty, gave notice in Dec 1934 that they would be withdrawing from the 1922 Treaty. It was however hoped that they might be persuaded to rejoin, or at least not build ships hugely different from the limits set out in the 1936 London Treaty. Nowhere is that clearer than in Article IV(2) of the 1936 Treaty:-

"No capital ship shall carry a gun with a calibre exceeding 14 in. (356 mm.); provided however that if any of the Parties to the Treaty for the Limitation of Naval Armament signed at Washington on 6 February 1922, should fail to enter into an agreement to conform to this provision prior to the date of the coming into force of the present Treaty, but in any case not later than 1 April 1937, the maximum calibre of gun carried by capital ships shall be 16 in. (406 mm.)."

Japan didn't sign up so the gun limit reverted to 16" on 1 April 1937.

The problem for Britain was that it needed to start its capital ship building programme as soon as possible after 31 Dec 1936 and couldn't afford to wait for a Japanese decision in the first 3 months 1937 to design a new capital ship. KGV and POW were laid down on 1 Jan 1937 after a lengthy design period. At one point in late 1935, for the space of only a few weeks, the Admiralty's choice was a battleship armed with 9x15" (3x3). Then came the 1936 Treaty.

The US on the other hand felt it could wait a bit longer, allowing the North Carolina design to be changed to incorporate the 16" gun in time to have the ship laid down in Oct 1937.

I think most signatory nations tried to comply with the 1922 Treaty, or at least no one set out to disregard them completely. One of the problems was that ship design was not an exact science. Until Washington, no one had tried to build a ship to a theoretical figure of "standard displacement" tonnage before. Everyone, including Britain, played the "game" to a greater or lesser extent (e.g. including a load of ammo in magazines capable of holding more in the event of war).

So you get the problems of the 10,000 ton Treaty cruisers. The Japanese tried to squeeze a quart into a pint pot, and found their ships had stability problems leading to weight increases to fix them. So the Myokos came out about 11,000 tons. On the other hand, despite starting later and being able to see what other nations had achieved, the US Pensacolas came out significantly underweight.

Germany of course was not a signatory to the Washington Treaty. What it could or could not do was governed by the Versailles Treaty of 1919. Hence it was able to build the Deutschlands as replacements for its old Battleships that needed replaced. Germany's next constraint was the Anglo German Naval Agreement of 1935 that allowed it to build up to approx 35% of the RN tonnage.

Interesting, thank you.
I was under the impression that while the Admiralty were not specifically bound to the constraints of the treaty after a certain point, they continued to order ships within the parameters, in a hope that other nations may still as well, as an attempt to keep costs down. Britain still obviously reeling from the financial affects of WWI

 

[Wild_Bill_Kelso]

Did the RN have any cruisers with substantial air assets, like the Tone with it's five E13s? The E13 had a substantial range of ~1,200 miles / 14 hours endurance, which made it quite effective in the recon and probably also in the ASW role. It could also carry a 250kg bomb or a depth charge. I know the British had the Walrus but it suffers quite a bit by comparison. The US OS2U was kind of in between.

Some Japanese warships (not sure if just battleships or also cruisers) also carried the Mitsubishi F1M, which was a biplane with a relatively short range, but apparently quite maneuverable and equipped with forward firing guns, it proved capable of shooting down enemy scouts like those OS2Us etc. , and sometimes sinking PT boats and so on.


If SR6 continues this, I'm interested to see how the IJN vs. RN submarines match up. The IJN had planes on some of their submarines too.

 

[RCAFson]

But of those 21 old cruisers 4 were AA cruisers armed only with 4" guns and lighter AA (Coventry, Curacao, Carlisle & Cairo) while Cardiff had been a Gunnery Training Ship since being withdrawn from the front line in Oct 1940.

And Delhi was being converted to an AA cruiser in the USA with a main armament of 5x5"/38. She didn't return to service until May 1942 after further work in Britain plus trials etc.

Frobisher didn't rejoin the fleet until Jan 1942, having been rearming since the outbreak of WW2. She had a low priority so the work took a long time.

Nov/Dec 1941 was costly for the RN/RAN historically. Ark Royal, Barham, Sydney, Neptune & Galatea all sunk. QE & Valiant put out of action at Alexandria.

And of the 6x5.25" armed Didos, Cleopatra only completed in Dec 1941 (as did the 4.5" armed Charybdis) but Phoebe was in the USA undergoing major repairs for torpedo damage suffered in Aug and didn't return to the fleet until July 1942.

Edit - and don't forget the old HMAS Adelaide.

With no war in the ETO/MTO the plan was to convert two D-class cruisers to AA cruisers, each with 8 - 4.5in guns.

The need to concentrate on escort production delayed the completion of many larger ships.

 

[Shortround6]

Interesting, thank you.
I was under the impression that while the Admiralty were not specifically bound to the constraints of the treaty after a certain point, they continued to order ships within the parameters, in a hope that other nations may still as well, as an attempt to keep costs down. Britain still obviously reeling from the financial affects of WWI

That is part of it. EwenS has the general consensus down pretty good. In the 1920s everybody was pretty much trying to follow the treat guidelines. But the only real limits were on Battleships, carriers and heavy cruisers. And the limits on carriers were pretty much to stop flagrant cheating. "No, that 25,000 ton ship with 6 14in guns and 6 planes on the back is NOT a carrier". Other limits include the age of the ships, you could not get rid of new ship ship that was only 5 years old and replace it with an even newer ship. There was a lot of language about was allowed and not allowed for refits/improvements.
Now because of the treaty limits the 8in gun cruisers became defacto 2nd class battleships or modern Armored cruisers like the pre-dreadnought armored cruisers. Nobody had much for new armored cruisers, anybody that could afford armored cruisers could afford battlecruisers. So everybody's had old armored cruisers from before about 1910 that needed replacing anyway.
10 years later and having seen the great Cruiser Race the British were in no mood or financial position to engage in Cruiser Race II and the British needed a crap load of smaller cruisers to stop merchant raiders and not small, short range, battle fleet 3.
The British were trying to get both the size of cruisers down so they could build larger numbers and they needed to replace the old battleships, in part due to age. The British had put more miles on their early WW I battleships and they needed more overhauls/rebuilding just to say in service.

The cheating thing picks up in the late 20s and into the early 30s and by the end of the 30s the more flagrant people were outright lying and everybody knew it.
1927-28 cruisers.
Northhampton.................9006 tons.............32.5 kts..............................107,000hp
Norfork................................9995 tons............32.3 kts.................................80,000hp
Suffren.................................9938 tons.............31 kts....................................90,000hp
Zara...................................11,680 tons............32 kts....................................95,000hp
Takao. Advertised............9850 tons..............35.5 kts..............................130,000hp
Takao, actual..................11,350 tons..............35.5 kts..............................130,000hp
Takao as rebuilt.............13,400 tons.............35.5 kts..............................130,000hp

Some were some faster cruisers built before and after these ships from all 5 navies. But the scope for cheating was huge. Not all navies built machinery to the same standards of efficiency or reliability. Not all navies ran their trials under the same conditions (some Italian cruisers ran speed trials without the turrets fitted) Trying to figure out if the armor was really as thin as the country claimed (lighter in weight) or covered as much area needed careful internal inspection which foreign countries were not going to get.

Some of the battleship rebuilds were classes in creative accounting and story telling. All of the older BB were allowed 3,000 tons of "improvements" which was supposed to be used for heavier deck armor and better torpedo protection. The 3,000 tons was regardless of the original size of the ship and not based on a percentage. The real loophole was that the 3,000 tons was supposed to be the total weight change after everything was done. Italians took their old 13 gun ships, cut them down the machinery level, pulled out the turbines and boilers and replaced them with higher powered machinery that weighed 1400 tons (?) less, removed Q turret (a triple) and associated armor/magazine, added to the bow, added a crap load of armor, replaced the entire secondary battery, installed an AA battery and managed to keep the total increase in weight to somewhat plausible 3000 tons as agreed to.
Italy had money to burn, well they didn't but Benito had ambition to burn and this was a way to get around the treaty. France was pouring money into the Maginot line and rebuilding the old WW I Dreadnoughts was a waste of money. The Bretagne class was laid down between the Iron Dukes and the QEs and completed between the QEs and the R Class so they were dated in several areas.

In countries like the US and Britain things were a bit harder to hide. The British tried to keep cost down because with size of the empire they need numbers of ships, not expensive rarities. If the British tried to build up the treaty limits in capability they would have faced a building war which they could not afford. The British were hoping to modify the treaties to allow greater numbers of cheaper ships.

 

[EwenS]

With no war in the ETO/MTO the plan was to convert two D-class cruisers to AA cruisers, each with 8 - 4.5in guns.

The need to concentrate on escort production delayed the completion of many larger ships.

The plan to convert the C class ships kept chopping and changing between 1936 and 1939. First it was the remaining 11 (Coventry and Curlew having already been converted on an emergency basis in 1935/36 as a result of the Abyssinian Crisis). Then 8, excluding the 3 ships of the Caledon group with a different armament layout. 1939/40 Cairo, Calcutta, Curacao and Carlisle were converted but the outbreak of WW2 saw the already planned conversion of Capetown & Colombo cancelled. These ships proved so useful that Colombo and Caledon were converted in 1942/43 to a modified design.

But without WW2 the Treaty system would have continued and 5 of the C class would have had to be scrapped in 1941. Friedman "British Cruisers".

As for the D class, the plan from 1936 was to convert ALL 8 to AA ships armed with 8x4.5" in twin mounts, a quad Pom Pom and 2 quad 0.5"and not just 2 of them. Conversion was expected to take 12 months with the first 3 beginning in Jan 1940, another in May and the other 4 in early 1941.

In mid-1939 the Admiralty formulated plans for what it would do in the event of war around Oct 1939. Part of this was to sacrifice the D class conversions BUT continue with the production of their guns for use in a future cruiser project. There was a design for one in early 1940 with 2 ships tentatively pencilled in, but the project fell by the wayside in summer 1940. (Moore "Building for Victory" and Friedman).

Also as part of that mid-1939 planning 4 more Didos were to be ordered on the outbreak of war. (Moore again).

When war did break out it was decided to use two sets of guns intended for the D class in the Didos Scylla and Charybdis, in the hope of having these ships in service sooner than if they were built with the planned armament. Their planned completion dates with the new armament were then expected to be Nov/Dec 1940. Unfortunately that aspect didn't work out and they didn't complete until Jun 1942 and Dec 1941 respectively.

Also on 4 Sept the Admiralty ordered 6 more Didos instead of the planned 4 based on an assessment of shipbuilding capacity. The reasoning was that the 5.25" turrets originally intended for S & C would be ready in 1941/42 in time to be put in these extra hulls. (Moore)

At the end of 1940 the Admiralty had an interest in the USN Mk37 director and its associated 5"/38 guns. Agreement was obtained for 2 ships to be converted, initially in a Canadian yard due to US Neutrality laws. All the problems disappeared with Lend Lease in March 1941. But the Admiralty wanted the system tested before allowing the second ship (Dunedin) to begin conversion due to bad experience with US 14" guns in WW1. By the time the first ship, Delhi, was ready, PH had happened and the US needed all the 5"/38 and Mk.37 director's it could get, so the project was cancelled.

In addition to that there was a tentative plan in 1938 to modernise Frobisher and Hawkins with 6 twin 5.25" turrets. which did not progress very far due to the expected lack of turrets.

Another possibility without war in Europe is that the London modernisation might have included new machinery and been extended to the other ships of that group. Maybe that would have prevented her hull cracking problems.

So in summary, without war in 1939 there would be 2-4 more C class AA conversions and 8 D class 4.5" AA conversions (maybe modified to include 2 with US armament). But the Dido programme would have been limited to 10 5.25" armed ships by mid-1941.

Without all the changes on the outbreak of war the Fiji programme would have run to 13 ships (11 historical) with completions through to late 1942.

Beyond that the cruiser programme becomes very confused with a lot of proposals in 1939/40 that came to nothing, until repeat Fijis were ordered in 1941/42. Maybe the 8" Admiral class cruiser might have gone ahead but with the need to develop new turrets (a gun design was already in progress) it would have been much later on the scene.

 

[Shortround6]

Did the RN have any cruisers with substantial air assets, like the Tone with it's five E13s? The E13 had a substantial range of ~1,200 miles / 14 hours endurance, which made it quite effective in the recon and probably also in the ASW role. It could also carry a 250kg bomb or a depth charge. I know the British had the Walrus but it suffers quite a bit by comparison. The US OS2U was kind of in between.

The larger between the wars Cruisers were supposed to carry up to 3 aircraft. The Swordfish and Shark were both float capable. The specs called for the Albacore but I am not sure it went anywhere.

Not sure if the catapult would handle the load. The idea getting the torpedo to the catapult might have given the officers tasked with carrying out the move the heebie-jeebies

Sometimes you have to decide what the mission/s are and stick with them. Using 3-4 planes as a strike group needs a lot of luck. it also needs a dedicated magazine and/or dedicated bomb lifts. Which affect both water and fire spread integrity. Most Cruisers had enough trouble flying the planes as recon planes unless you are willing to write off the crews.

Some Japanese warships (not sure if just battleships or also cruisers) also carried the Mitsubishi F1M, which was a biplane with a relatively short range, but apparently quite maneuverable and equipped with forward firing guns, it proved capable of shooting down enemy scouts like those OS2Us etc. , and sometimes sinking PT boats and so on.

Might have been desperation. Since the Japanese AA pretty much sucked maybe using the F1M was more effective than using the ships own AA?

If SR6 continues this, I'm interested to see how the IJN vs. RN submarines match up. The IJN had planes on some of their submarines too.

I am hoping to get to the subs at some point. Here is a major difference in the Japanese and everybody else's subs.
By the 1930s the Japanese idea of a "small" sub (not miniature) was about the size of everybody else's large or very large subs. The Japanese routinely built large subs the size of everybody else's one-offs or experimentals.
The Japanese needed range/endurance even more than the US did. They also needed high speed for the "fleet" role.
Problem is that big subs are easier to spot from the air or surface. They are slower to dive, they don't turn as well and they are bigger sonar targets.
Of course if you can't reach the target area none of that matters since you won't be attacking anyway. This goes both ways, if you get sunk on the way to the target area because of the Subs size it is no good.
The Japanese sub designers might have been quite good, they just had a problem that many other sub using countries didn't have.
This is what makes it very hard to compare the Japanese boats head to head with anybody else's boats.

The British built this thing in 1921-25 but the engines were unreliable and it was laid up in 1933 and scrapped in 1937.
four 5.2in guns.

 

[EwenS]

The need to concentrate on escort production delayed the completion of many larger ships.

Which escorts are you thinking about?

The Flower class were mainly built in mercantile yards not the big naval yards. The exception was Harland & Wolff in Belfast who dedicated 2 slips to their production on an almost production line basis from the outbreak of war.

Production of Black Swan class sloops would probably have continued at a rate of a couple per year. But the increased production of the 1940/41 Programmes built in the smaller naval yards weren't laid down until 1941 and it was late 1942 before these began to appear historically.

The big programme affecting the naval yards were the Hunt class escort destroyers in the various 1939 and 1940 Programmes (86 ships completed through to 1943) and the various Intermediate destroyers of the 1939 War through 1942 Programmes (2,4,5 & 3 flotillas per year, total 112 ships completed through to 1947). But in the absence of these ships in the yards there would have been some kind of replacement to follow on from the L&M classes. The pattern from the mid-1930s had been to order 2 flotillas, total 16 ships, per year (except for 1938 when none were included). ISTR seeing a design with 4 turrets of the L class. But the problem was the complexity and cost of these large destroyers resulting in the N class in 1939 as a repeat J/K to keep cost down. But there was the need to tackle ships like the large Japanese destroyers.