What would have happened if the Washington Naval Treaty and the London Naval Treaty were completely incapacitated in 1934?

[Username666]

• Joffre laid down on 26.11.38 and it was planned that she would be launched in 1941 but my source didn't have a planned completion date.
• Painlevé hadn't been laid down before France fell and it looks like the 40,000 ton Battleship ordered from the same yard was given priority over her.

From what I heard before, the French Navy in interwar period had a lot of trouble abut building battleships and aircraft carriers because of dock problems, is that related?

 

[Username666]

Well, anyway, thanks to you, I learned a lot. Thank you so much!

And on the other hand, it occurred to me that I had a pretty conservative view of alternative history.

Because I didn't think that even if the two treaties were broken in 1934, it would be very different from the original history because of the economic situation at the time.

 

[Hood]

I think it might have been why only 2 Mogador class were built when French destroyers operated in divisions of 3. However, I didn't check the book first. This is why I think France wouldn't be able to build more warships from December 1934 even if they wanted to.

This does seem to have been a problem.
Looking through Conway, Whitley etc. the other it struck me how destroyer and cruiser construction seems to peak around 1936-37 in terms of commissioning and then drops off a cliff with most of the new construction not laid down until 1938-39, which implies an ordering gap.

I've already written that I think they'd continue to build Edinburgh class instead of the Colony class and its successors if there was no 2nd LNT or a less restrictive Treaty retained the 10,000 ton limit for Cruisers in the previous Treaties. Now I think that they'd also build another 16 Amphion class Cruisers of 7,000 tons instead of the 16 Dido class.

The only thing against more Edinburghs is that there were at least three graving docks around the Empire that the Southamptons could use that the Edinburghs couldn't because of their increased length- it's easy to forget they were the largest cruisers built after the Counties (the carrier-sized 20,000 tons heavies would have been an equal basing nightmare I suspect).
The only thing against the Amphions is that the Admiralty viewed them with distaste because they had been conceived as a sop to Geneva in an attempt to encourage other navies they didn't need to build up to the 10,000 ton limit but everyone else just laughed and built 10,000 tonners (usually actually way over that with cheating). Therefore the Edinburghs were ironically the outcome of that - to fully build up to the limit with fewer constraints. So that would tend to cloud their judgement that a 6in cruiser should be 10,000tons to match the Joneses. In any case with the triple turret its just as easy to build a 3x3 6in cruiser - effectively a Colony. I'm not sure that a Amphion with improved armour would work out much cheaper in terms of displacement or cost.

Being AA cruisers the Didos could be 5,600 tons and the Admirals were happy with that as they were for AA and not a traditional 6in cruiser. Given the numbers of C and Ds that needed replacing it was obvious that smaller cruisers would be needed - Italy, France and (to a lesser extent) Japan didn't have the same problem as they had few overage WW1 relics to replace.
I'd prefer a 6x2 5.1in DP BD mounting Dido personally.

 

[EwenS]

• Joffre laid down on 26.11.38 and it was planned that she would be launched in 1941 but my source didn't have a planned completion date.
• Painlevé hadn't been laid down before France fell and it looks like the 40,000 ton Battleship ordered from the same yard was given priority over her.

From what I heard before, the French Navy in interwar period had a lot of trouble abut building battleships and aircraft carriers because of dock problems, is that related?

The building dock at the Arsenal de Brest was not long enough for Dunkerque. The foremost part of her bow was built separately and added on after she was placed in a separate dry dock for completion. Richelieu was built in the same facility but had separate bow and stern sections. And Clemenceau followed Richelieu.

The result was construction of a new building dock and associated dry docks were begun but not completed until after WW2. These were intended to take the largest ships then envisaged in the form of the next battleship generation that never appears.

Strasbourg was built on the only large slip at Ateliers at Chantiers de la Loire yard in St Nazaire. She was followed by the carrier Joffre.

Jean Bart was built at a brand new and unusual facility at the AC Loire yard in St Nazaire and was intended to be followed by Gascoyne.

These seem to have been the only sites available to build vessels larger than cruisers.

 

[Username666]

The building dock at the Arsenal de Brest was not long enough for Dunkerque. The foremost part of her bow was built separately and added on after she was placed in a separate dry dock for completion. Richelieu was built in the same facility but had separate bow and stern sections. And Clemenceau followed Richelieu.

It's similar with the HBCM(Hull Block Construction Method).

Anyway, the dock that built Dunkerque, Richelieu and Clemenceau built must have been very short.

 

[NOMISYRRUC]

I think it might have been why only 2 Mogador class were built when French destroyers operated in divisions of 3. However, I didn't check the book first. This is why I think France wouldn't be able to build more warships from December 1934 even if they wanted to.

This does seem to have been a problem.
Looking through Conway, Whitley etc. the other it struck me how destroyer and cruiser construction seems to peak around 1936-37 in terms of commissioning and then drops off a cliff with most of the new construction not laid down until 1938-39, which implies an ordering gap.

I think the ordering gap had a lot to do with France and Italy trying to have naval parity with each other. For example, the gap between the French La Galissonnière & De Grasse classes may have been because there was a gap of several years between the Italians ordering the 5th & 6th Groups of Light Cruisers or vice versa.

Prior to reading John Jordan's books on Scribd I though that although France & Italy didn't accept limitation on the size of the Submarine, Cruiser & Destroyer forces under the 1st LNT they had a "gentleman's agreement" between themselves over these types of warship and that's for example why they both built 7 Heavy and 12 Light Cruisers. However, Jordan wrote that they tried and failed to make one in the early 1930s.

However, when one looks at the construction dates there is a loose correlation between the 19 Cruisers that France completed 1926-37 and the 19 Cruisers that the Italians completed 1928-37.

France had 7 Heavy and 12 Light Cruisers on 03.09.39 plus one under construction and 2 on order.
3 Cruisers to replace the Duguay Trouin class were authorised in 1940.
Details are a mix of the John Jordan book on Scribd and Conway's 1922-46.



Italy had 7 Heavy & 12 Light Cruisers on 10.06.40 plus 2 on order.
Details are according to Conway's 1922-46

​

Another reason for the gap may be that the Capital Ships both nations built in the 1930s absorbed most of the available funds and industrial resources for new naval construction. E.g. Littorio & Vittorio Vento were to have been completed by the end of 1938 and one of the reasons for the delay of about 18 months (according to Erminio Bagnasco's book on Scribd) was that a large number of submarines was being built at the same time and they used the same type of steel which was in insufficient supply.

 

[NOMISYRRUC]

The building dock at the Arsenal de Brest was not long enough for Dunkerque. The foremost part of her bow was built separately and added on after she was placed in a separate dry dock for completion. Richelieu was built in the same facility but had separate bow and stern sections. And Clemenceau followed Richelieu.

It's similar with the HBCM(Hull Block Construction Method).

Anyway, the dock that built Dunkerque, Richelieu and Clemenceau built must have been very short.

I recommend that you read this as it explains it much better than I can and is where I found a lot of the information that I've been using here.

French Battleships, 1922–1956

This illustrated naval history presents a comprehensive study of French battleships constructed after the Washington Naval Treaty of 1922. The French battleships of the Dunkerque and Richelieu classes were the most radical and influential battleship designs of the interwar period, and were...

www.scribd.com

I think it's well worth paying the subscription.

 

[NOMISYRRUC]

I've already written that I think they'd continue to build Edinburgh class instead of the Colony class and its successors if there was no 2nd LNT or a less restrictive Treaty retained the 10,000 ton limit for Cruisers in the previous Treaties. Now I think that they'd also build another 16 Amphion class Cruisers of 7,000 tons instead of the 16 Dido class.

The only thing against more Edinburghs is that there were at least three graving docks around the Empire that the Southamptons could use that the Edinburghs couldn't because of their increased length- it's easy to forget they were the largest cruisers built after the Counties (the carrier-sized 20,000 tons heavies would have been an equal basing nightmare I suspect).

However, we don't know how many graving docks around the Empire were large enough for an Edinburgh. Though my copies of Jane's 1938-40 might tell us.

For what it's worth these are the overall lengths of the larger British Cruisers according to Douglas Morris in "Cruisers of the Royal and Commonwealth Navies".

• 555½ feet - Fiji, Newfoundland & Swiftsure classes.
• 575 feet - York class.
• 591½ feet - Southampton & Gloucester classes.
• 605 feet - Cavendish class which is what he calls the Hawkins class.
• 613½ feet - Edinburgh class.
• 630 feet Kent class.
• 633 feet London & Dorsetshire classes.

The Edinburgh class was 20 feet longer than the Southampton & Gloucester classes and about 20 feet shorter than the County classes. There were 17 Cruisers that were longer than the Edinburgh class, i.e. the 13 Counties and 4 Cavendish/Hawkins class.

Please confirm that you're saying that the Counties and Edinburghs were a basing nightmare. I find it hard to believe that the Royal Navy would build so many Cruisers that were intended to be Trade Protection ships if there weren't enough graving docks around the Empire to support them.

Especially as Morris says that the original plan was to build 40 Counties in the 1924-25 to 1928-29 Programmes at the rate of 8 per year. Although Friedman (in Vol. 2 of his British Cruisers books) & Roskill (in "Naval Policy between the Wars: Vol. 1") say 8 Cruisers a year in the 3 Programmes 1924-25 to 1926-27 and after that 4 per year. At the time the requirement was 70 Cruisers a year including 10 that could be over age and as at that time the service life of a Cruiser was 15 years an average building rate of 4 Cruisers a year was required.

 

[Hood]

Please confirm that you're saying that the Counties and Edinburghs were a basing nightmare. I find it hard to believe that the Royal Navy would build so many Cruisers that were intended to be Trade Protection ships if there weren't enough graving docks around the Empire to support them.

Not a nightmare as such - more of a headache in wartime if you have too many damaged ships requiring the same graving docks. In peacetime its less of an issue. I'll have to dig out which docks they were, one of them was on Malta I think.

Another reason for the gap may be that the Capital Ships both nations built in the 1930s absorbed most of the available funds and industrial resources for new naval construction. E.g. Littorio & Vittorio Vento were to have been completed by the end of 1938 and one of the reasons for the delay of about 18 months (according to Erminio Bagnasco's book on Scribd) was that a large number of submarines was being built at the same time and they used the same type of steel which was in insufficient supply.

That would seem the most likely explanation - in my what-if 1942 Far East war thread back in 2020 I did ponder the rather lacklustre performance of the Italian shipbuilding industry 1939-43.
I wrote at that time:

Italian shipbuilding during the war was not a huge success.
The Venetos took about six years each to build and Impero was never completed.
Aquila was a substantial reconstruction, nearly completed just as Mussolini's regime crumbled. The more basic Sparviero was more akin to a large merchant carrier the British were converting rather quickly. Only begun in 1942 the time ran out before much more than stripping her superstructure was completed.
No heavy or light cruiser was completed after 1937, the two Cianos being cancelled even before she entered the war. Even the two Thai cruisers taken over were never completed due to material shortages.
Twelve Capitani Romanis were laid down during September-October 1939, a rather grandiose gesture that must have caused bottlenecks in material and armament and engines. Despite being relatively small 3,600 ton unarmoured ships, only three were ever completed nearly 4 years later.
No fleet destroyers were laid down between 1937 and 1940, just 7 repeat Soldatis. The following D'Oro-class was a sound design but the crash programme of 20 ships barely got onto the slips, only 9 being laid down just months before Italy was out of the war.
The bulk of the wartime destroyers built were the Ciclones, repeats of the 1933-35 Orsa-class and it was late 1942 before most of these completed, only 16 being built. More escorts were sought and in 1942 the Spica was enlarged as the Ariete, a 745-ton torpedo boat, 42 were planned but actually these small ships did relatively well with 16 completed for the Italians or the Germans. The true escort corvette, the Gabbiano-class, was built in bulk and at speed but again it was 1942 before Italy reacted to its wartime needs and most of them again fell into German hands.
During the 1930s the Italians had been churning out submarines, by 1940 most had been completed. Wartime construction totalled about 22 completed submarines, most of the Flutto series submarines never completed and the Romolos were an interesting way to try and beat the Allied blockade but perhaps a waste of precious resources.

Some of these problems outlined were due to the war cutting off supplies and material but its clear that naval shipbuilding (apart from submarines) tailled off quite dramatically during 1937-40 and even for 1941 little new construction seems to have been planned. This suggests cost cutting by reducing naval construction expenditure. There seems to have been a lack of foresight about escorts and certainly it took the Italians too long to begin any kind of wartime construction programme which never really got going until 1942 with any momentum.
In my scenario its possible some of the planned sloops and auxiliaries may have been started during 1941, the diesel-powered Orsa derivative might have taken a while to come to fruition until the engines were ready, a pair of Cianos would probably have been built as planned but I doubt much concrete would have been accomplished by 1942 towards a proper 'breakout fleet'.

By 1940 the Italian Navy were already down the industrial priority list behind the Army and the Air Force and their shipbuilding industry could just not make up any shortfalls in capacity. Interestingly your analysis of cruisers shows that both nations were using around six yards for their cruisers. Both nations do seem rather equally matched in industrial capability and funding and perhaps its not surprising that they both managed to keep up with each other. My gut feeling is that from 1941 France would have overtaken Italy. The lamentable record Italy had in construction 1940-43 is not good for a naval power with a major campaign right on its doorstep. If war couldn't provide the necessary impetus then I don't see peacetime providing it.
(Now I ponder it I wonder how well they compare given that Vichy France managed to complete some of its ships, in addition post-Toulon Italy got few of its share of the spoils operational, unlike the Germans).

 

[NOMISYRRUC]

I've already written that I think they'd continue to build Edinburgh class instead of the Colony class and its successors if there was no 2nd LNT or a less restrictive Treaty retained the 10,000 ton limit for Cruisers in the previous Treaties. Now I think that they'd also build another 16 Amphion class Cruisers of 7,000 tons instead of the 16 Dido class.

Being AA cruisers the Didos could be 5,600 tons and the Admirals were happy with that as they were for AA and not a traditional 6in cruiser. Given the numbers of C and Ds that needed replacing it was obvious that smaller cruisers would be needed - Italy, France and (to a lesser extent) Japan didn't have the same problem as they had few overage WW1 relics to replace.

If I remember correctly from reading Friedman the Dido class (in common with the American Atlanta class) weren't designed to be AA Cruisers, they were designed to be Fleet Cruisers supporting the Destroyer Flotillas. That's why both had a large number of quick firing guns (to smother the enemy's Destroyers with gunfire) that coincidentally were capable of engaging aircraft.

Rounds per minute according to the Naval Weapons website.

• 6-8 - 6in Amphion class.
• 7-8 - 5.25in Dido class except Charybdis & Scylla.
• 12 - 4.5in Charybdis & Scylla
• 15-20 - 4in Amphion class.

Therefore, rounds per minute per ship in surface warfare:

• 70-80 Dido class, except that only 6 out of 16 ships were completed with ten 5.25in guns.
  • 56-64 for the 8 ships completed with eight 5.25 in guns.
  • 96 for the 2 ships completed with eight 4.5in guns.
• 48-64 Amphion class which fired heavier ammunition.
• Plus the Amphons had eight 21in torpedoes instead of the Didos six.

And, rounds per minute per ship in anti-aircraft warfare:

• 70-80 Dido class, except that only 6 out of 16 ships were completed with ten 5.25in guns.
  • 56-64 for the 8 ships completed with eight 5.25 in guns.
  • 96 for the 2 ships completed with eight 4.5in guns.
• 120-160 Amphion class, but they were lighter shells.

As completed the Amphions had a slightly heavier light AA armament than the First Group of Didos.

• 8 x 2pdr (2 x 4) in both classes.
• 12 x 0.5in (3 x 4) Amphion class vs. 8 x 0.5in (2 x 4) Dido class.

So I think the Amphion class were better AA ships in practice.

I'd prefer a 6x2 5.1in DP BD mounting Dido personally.

No more British gun calibres. Please! There were too many as it was. One of the reasons why I want no Dido class (rather than I think there would be no Dido class) is to reduce the number of gun calibres.

 

[Username666]

The building dock at the Arsenal de Brest was not long enough for Dunkerque. The foremost part of her bow was built separately and added on after she was placed in a separate dry dock for completion. Richelieu was built in the same facility but had separate bow and stern sections. And Clemenceau followed Richelieu.

It's similar with the HBCM(Hull Block Construction Method).

Anyway, the dock that built Dunkerque, Richelieu and Clemenceau built must have been very short.

I recommend that you read this as it explains it much better than I can and is where I found a lot of the information that I've been using here.

French Battleships, 1922–1956

This illustrated naval history presents a comprehensive study of French battleships constructed after the Washington Naval Treaty of 1922. The French battleships of the Dunkerque and Richelieu classes were the most radical and influential battleship designs of the interwar period, and were...

www.scribd.com

I think it's well worth paying the subscription.

Thank you very much! I'll buy it if I have a chance later!

 

[NOMISYRRUC]

That would seem the most likely explanation - in my what-if 1942 Far East war thread back in 2020 I did ponder the rather lacklustre performance of the Italian shipbuilding industry 1939-43.

I wrote at that time:

The Venetos took about six years each to build and Impero was never completed.

Twelve Capitani Romanis were laid down during September-October 1939, a rather grandiose gesture that must have caused bottlenecks in material and armament and engines. Despite being relatively small 3,600 ton unarmoured ships, only three were ever completed nearly 4 years later.

There seems to have been a lack of foresight about escorts and certainly it took the Italians too long to begin any kind of wartime construction programme which never really got going until 1942 with any momentum.

In defence of the Regia Marina and the naval-industrial complex behind it.

The Littorio class.

• Yes Littorio & Vittorio Vento took about 5½ years to build which was about 18 months longer than planned. According to Erminio Bagnasco's book on Scribd another reason why they took longer to build than planned was that the design hadn't been completed when they were laid down.
• Roma was built in 39 months.
• Impero was laid down 4 months before Roma.
  • Impero was launched 18 months after she was laid down.
  • Roma was launched 21 months after she was laid down.
  • Unfortunately, for Impero it was decided to tow her from Genoa to Trieste for completion to avoid the risk of being damaged in air raids in the impending war with France and happened to be at Brindisi on 10.06.40. She didn't resume her journey to Trieste (via Venice) until 22.01.42.
• I think that if they had taken the risk of Impero being damaged by a French air raid on Genoa, she'd have been completed 4 months before Roma, i.e. in February 1942 versus June 1942.

I regard the Capitani Romanis as very large Destroyers rather than very small Cruisers equivalent to the French Mogador class contre-torpilleurs and the Mogador class in the French 1940 Programme may have been intended as replies to them. I don't know but suspect that the Capitani Romanis were intended to be replacements for the Navigatori class which would be becoming overage (according to the 1st LNT) by the time the Capitani Romanis would have been completed.

Although the RM only had a handful of specialist escort vessels it did have 59 Fleet Destroyers and 33 old & 34 new small Destroyers of the Torpedo Boat type making a total of 126 Destroyers of all types. They also had a few score of RD type minesweepers that were launched between 1916 & 1923 that were still fit for purpose, plus 4 Fasana & 6 Ostia class minelayers cum minesweepers launched in the second half of the 1920s.

Given that the RM faced a strong surface threat to its coastal shipping and the supply lines to Libya & the Italian islands in the Aegean it was better to do build the small Destroyers of the Pegaso and Spica classes than build large numbers of equivalents to the British sloops.

If I was in the Italian Admiralty and Italy had more money & more shipbuilding capacity in the 1930s I'd have built more Spica & Pegaso class Torpedo Boats to replace the old Torpedo Boats and more minelayers cum minesweepers of the Fasana & Ostia classes to replace the RD type minesweepers.

I'd also say that when Italy declared war it looked as if was all over apart from negotiating the peace treaty and would only continue for a few weeks or at the most a few months. If Mussolini had known that by the end of the year he'd be mired in a long war, which is country was not capable of fighting, he wouldn't have come to the aid of what he thought was the winning side in the first place, i.e. he'd have maintained Italy's non-belligerent status instead of declaring war on France and the UK.

I think that expecting to be fighting a short war that would last no longer than a few months was an important reason why it took such a long time for Italy to start building the Commandanti Medaglie D' Oro, Ciclone, Ariete & Gabbiano classes.

 

[NOMISYRRUC]

I've already written that I think they'd continue to build Edinburgh class instead of the Colony class and its successors if there was no 2nd LNT or a less restrictive Treaty retained the 10,000 ton limit for Cruisers in the previous Treaties. Now I think that they'd also build another 16 Amphion class Cruisers of 7,000 tons instead of the 16 Dido class.

The only thing against the Amphions is that the Admiralty viewed them with distaste because they had been conceived as a sop to Geneva in an attempt to encourage other navies they didn't need to build up to the 10,000 ton limit but everyone else just laughed and built 10,000 tonners (usually actually way over that with cheating). Therefore the Edinburghs were ironically the outcome of that - to fully build up to the limit with fewer constraints. So that would tend to cloud their judgement that a 6in cruiser should be 10,000 tons to match the Joneses. In any case with the triple turret its just as easy to build a 3x3 6in cruiser - effectively a Colony. I'm not sure that a Amphion with improved armour would work out much cheaper in terms of displacement or cost.

My reading was that the Leanders & Amphions were the Cruisers that the Admiralty preferred because they were fit for purpose and cheap enough to be built in the numbers it wanted. As you wrote it was forced to build the Towns, Colonies & Swiftsures to keep up with the Joneses.

Costs

These costs are from a Cabinet Paper called "Defence Expenditure in Future Years, October 1937".

£2,400,000 Norfolk​

£2,175,000 Glasgow (including aircraft £55,700)​

£2,200,000 Liverpool (including aircraft £55,700)​

£1,650,000 Dido​

£1,400,000 Penelope (including aircraft £22,000)​

£1,400,000 Aurora (including aircraft £22,000)​

Unfortunately, it didn't have the costs for the Amphion, Edinburgh & Leander classes.

Notes I made from "The Design and Construction of British Warships 1939-1945, Volume 1" by D.K. Brown say:

£2,000,000 per ship, Kent & London classes.​

£1,613,000 Leander class​

£1,200,000 Arethusa class​

£2,150,000 Edinburgh class​

£1,600,000 Dido class​

£2,230,000 Fiji class​

There were no costs for the other Colony classes and there weren't any for the York, Amphion, Southampton, Gloucester & Swiftsure classes either.

The costs are "Vote 8 costs" which refers to "Vote 8 Shipbuilding, Repairs, Maintenance, &c." of the Navy Estimates and therefore excludes the cost of their gun barrels & aircraft, which came under "Vote 9 Armament" for the gun barrels and (until the 1938-39 Estimates) "Vote 4 Fleet Air Arm" for the aircraft.

I also have a photocopy of Page 118 of the book that has a table of particulars of Cruiser designs from the Kent to Dido classes. At the bottom of the table were the Vote 8 costs. Unfortunately, it only had costs for the following classes.

£2,084,200 Kent class​

£1,966,350 London class​

£1,613,220 Leander class​

£1,193,000 Arethusa class​

£1,835,129 Southampton class​

£2,151,220 Belfast class​

£1,574,450 Dido class​

My copy of Jane's 1939 has the following costs:

£1,970,000 Kent class (average cost of) and cost of armament £700,000.​

£1,480,097 Ajax​

£1,500,000 Leander - Average cost of class - Cost £1.5M to £1.6m apiece.​

£1,422,727 Perth​

£1,434,579 Sydney​

£1,251,161 Arethusa​

£1,210,763 Galatea​

£1,290,787 Penelope​

£1,252,915 Aurora​

It didn't specifically say so, but due to their similarity to the costs in, D.K Brown's book, I think they were Vote 8 costs.

Although neither the Cabinet Paper, Jane's 1939 or D.K. Brown had a cost for the York class, Douglas Morris in his entry on the class in "Cruisers of the Royal and Commonwealth Navies" (Pages 187 & 188) says that the class hardly succeeded as economical alternatives to the 10,000 ton Counties as the one-eighth reduction in cost wasn't significant enough.

On that basis the costs of Exeter & York would have been:

£2,100,000 Total Cost ((£2,400,000 Norfolk in the Cabinet Paper ÷ 8) x 7 = £2,100,000))​

£1,750,000 Vote 8 Cost (Circa £2,000,000 a County in Brown & Janes ÷ 8) x 7 = £1,750,000))​

Based on the above I think an Amphion would cost about the same to build a Dido. It would also save the cost of the R&D to develop the 5.25in gun & its twin turret (because all the new Capital Ships were armed with 4.5in guns) and put them into production. As the twin turret on the Amphion used the same mark of 6in gun as the one in the triple turrets on the larger cruisers there's some potential for some production economies of scale for the guns & ammunition.

My guess is the Medium Size Cruiser armed with nine 6in guns in three triple turrets that you suggest would come out at around 7,000 tons like the Amphion with the same machinery and armour on the same scale so the same Vote 8 cost. Plus as it would have the nine 6in guns instead of eight with the same secondary & light AA armaments, nearly the same Vote 9 cost. It would also reduce the demand for gun pits of cruiser turret size as there would be three per ship instead of four and for all I know three triple turrets may be cheaper to build than four twin turrets.

According to the above the Vote 8 cost of an Amphon was about £1,450,000 and the cost of a Fiji was £2,230,000 so the latter cost 54% more than a Fiji but I suspect that the cost of the latter was distorted by wartime inflation. Therefore, if we use the cost of the Dido class instead that's £1,600,000 versus £2,230,000 and a difference of 39% which is still a significant difference. The standard displacements were 7,000 tons & 8,500 tons with a difference of 1,500 tons or 20% which is a significant.

However, in any case I'm talking about building a mix of Edinburghs and Amphions instead of the "Real World's" mix of Colonies and Didos. Here the difference in size and cost is significant. Vote 8 cost is £1,450,000 versus £2,150,000 producing a difference of 48% and 7,000 tons versus 10,000 tons producing a difference of 43%.

 

[NOMISYRRUC]

I'd prefer a 6x2 5.1in DP BD mounting Dido personally.

My personal ALT-Dido would be based on the Amphion class rather than the Arethusa class and be armed with twelve 5.25in guns in six twin turrets that could fire at the specified 10-12 rounds per minute instead of the actual 7-8 rounds per minute. These would be in the roomier version of the twin 5.25" turret fitted to Vanguard.

They'd displace 25% more (7,000 tons versus 5,600 tons) but only carry 20% more main armament (six twin turrets versus five) to account for the larger & heavier turrets and more rounds per gun in the magazines. It would also be able to take radar and more light AA guns more easily and the later ships of the class might not need to be fitted with five twin 5.25in turrets instead of six as weight compensation.

 

[NOMISYRRUC]

In any case with the triple turret its just as easy to build a 3x3 6in cruiser - effectively a Colony. I'm not sure that a Amphion with improved armour would work out much cheaper in terms of displacement or cost.

Vickers-Armstrong did it on a modified Arethusa hull displacing 6,500 tons at a cost (including gun barrels) of about £1,750,000.

​

The above is from Jane's 1940. However, some of the details above are different from her entry on Page 420 of Conway's 1922-46.

Displacement: 6,500 tons standard & 7,500 tons full load.​

Dimensions: 510ft pp, 541ft 2ft oa x 56ft 6in x 16ft 6in.​

Machinery: 4-shaft Parsons geared turbines, 4 Yarrow boilers, 54,000 shp = 30 knots.​

Armament: nine 6in (3 x 3), four 4in (4 x 1), eight 2pdr (8 x 1) and six 21 in torpedoes (6 x 2).​

Crew: 556 plus 60 cadets.​

​

That's 2,000 tons less than a Colony class and at a total cost £480,000 (22%) less than the Vote 8 cost of a Fiji class.

 

[Hood]

No more British gun calibres. Please! There were too many as it was. One of the reasons why I want no Dido class (rather than I think there would be no Dido class) is to reduce the number of gun calibres.

Ah but in my AU the 5.1in replaces the 4.5in, 4.7in and 5.25in so actually improves the situation quite a bit!

Vickers-Armstrong did it on a modified Arethusa hull displacing 6,500 tons at a cost (including gun barrels) of about £1,750,000.

I am quite fond of the La Argentina though its almost a direct analogue for the Amphion. It has one more gun and displaces slightly less but has inferior armour and is 2 knots slower. Giving the same armour and adding a bit of length the same 72,000hp would probably mean a 7,500 tonner though. I agree that on paper Amphion seems the better bargain. Against a Fiji, I'm less sure and we're not comparing quite like for like given Fiji has larger aircraft facilities etc. and is a 12-gun ship - even though X turret was later pruned as the design was overloaded it retained the same basic hull (albeit with more beam continually added). A 'Super La Argentina' is probably better than Fiji given that design was too ambitious and in this scenario we don't really need to worry about tonnage as much.

The other caveat I have is whether its possible to actually build enough triple and twin turrets and is that in itself wasteful?

If I remember correctly from reading Friedman the Dido class (in common with the American Atlanta class) weren't designed to be AA Cruisers, they were designed to be Fleet Cruisers supporting the Destroyer Flotillas. That's why both had a large number of quick firing guns (to smother the enemy's Destroyers with gunfire) that coincidentally were capable of engaging aircraft.

Yes they started out in 1933-34 as a 4,500-5,000 ton scout (6x1 or 2x3 6in) then 3,500 tons (5x1 6in, mostly unarmoured) but then abandoned in favour of the Tribal-class leaders. It became more of a destroyer flotilla leader during 1935 and options with 4.7in or 5.1in guns were looked at. The result was the same firepower as Tribal (no torpedoes though) on 4,700 tons which was massively wasteful. The 5.25in replaced the 5.1in and the design was pushed back, by 1936 torpedo tubes were added as the design became a general-purpose cruiser (3 ships were wanted) and HA/LA gunnery was now a key feature. The result was 5x2 5.25in on 5,100 tons. The design bloated a bit more to end up with the Dido as we know them.

The 5.25in was indeed chosen for its ship-stopping power and not AA prowess. The choices were not easy - single shielded 6in was anachronistic, anything less than 5in looked wasteful on a cruiser hull. I can't help but feel that messing around like this for 3 cruisers for niche roles (the Med command being particularly keen on the design but actually wanted for the Far East for a future war against Japan) was rather pointless. Tribal was the better choice as a leader - just because the RA(D) had been sailing around on a C or D-class cruiser wasn't a good case to build a direct replacement. General purpose does seem an odd category given that Arethusa was only 5,300 tons already - so yes I am coming around to your view that from a 1936 perspective the Arethusa is the better choice. From a 1941 perspective I would say not. My conclusion would be order another three Arethusas and then develop a proper AA cruiser with 12x 4.5in guns and 2 or 4x8 pom-poms.

The Didos seem to be the closest the RN got to IJN practice of using light cruisers as flotilla leaders - the Agano being designed for much the same role and emerging as a 6,600 ton cruiser (3x2 6in (55 degree elevation for AA barrage fire and ironically the gun was developed from a previous Vickers design!), 2x4 24in TTs, 35kts, 2.25in belt & 2-0.35in deck). The original design was 4x2 6in and 2x3 TT, so it lost gun power for torpedo power.
Both Arethusa or Dido look like a better bargain - slower but at least with decent armour.

Not a nightmare as such - more of a headache in wartime if you have too many damaged ships requiring the same graving docks. In peacetime its less of an issue. I'll have to dig out which docks they were, one of them was on Malta I think.

The docks were - Hong Kong No.1, Gibraltar No.2 and Malta No.5.

 

[NOMISYRRUC]

No more British gun calibres. Please! There were too many as it was. One of the reasons why I want no Dido class (rather than I think there would be no Dido class) is to reduce the number of gun calibres.

Ah but in my AU the 5.1in replaces the 4.5in, 4.7in and 5.25in so actually improves the situation quite a bit!

Fair enough. If anything you're underestimating the effect it would have.

• I think it would improve the situation a lot on the production & logistics side. Especially if it is also produced for the British Army instead of its 4.5in and 5.25in AA guns.
• Furthermore, if it had the same rate of fire as the 4.5in guns it was produced instead of the ships that had it instead of the 5.25in gun (i.e. the KGV class, Vanguard & the Dido class) would have a lot more firepower.
• Naval Weapons says the 5.25in had a ROF of 7-8 rounds per minute per gun. If the 5.1in fitted to a twin mounting had a rate of fire of 12 RPM per gun like the wartime twin 4.5in in twin mountings of the "Real World" that would increase the total RPM of the 16 guns on the KGV class from 112-128 to 192 and the Dido class ships with 10 guns from 70-80 to 120. That aught to more than make up for the lighter shells (62lb v 80lb according to Naval Weapons).

When do you think it would be ready for service? I think in time for Warspite to be fitted with 16-20 in 8-10 twin mountings (depending upon how heavy the gun, mounting and turret were) as part of her 1934-37 refit or even Repulse as part of her 1932-36 refit if it was upgraded to a "Renown style" rebuild, but that would increase the cost from about £1.8 million to about £3.1 million.

 

[NOMISYRRUC]

Vickers-Armstrong did it on a modified Arethusa hull displacing 6,500 tons at a cost (including gun barrels) of about £1,750,000.

I am quite fond of the La Argentina though its almost a direct analogue for the Amphion. It has one more gun and displaces slightly less but has inferior armour and is 2 knots slower. Giving the same armour and adding a bit of length the same 72,000hp would probably mean a 7,500 tonner though. I agree that on paper Amphion seems the better bargain. Against a Fiji, I'm less sure and we're not comparing quite like for like given Fiji has larger aircraft facilities etc. and is a 12-gun ship - even though X turret was later pruned as the design was overloaded it retained the same basic hull (albeit with more beam continually added). A 'Super La Argentina' is probably better than Fiji given that design was too ambitious and in this scenario we don't really need to worry about tonnage as much.

No because we are (or at least I am) not making a like-for-like comparison.

• The difference in displacement between a Dido and a Fiji was supposed to be about 43%, i.e. 5,600 tons v 8,000 tons (although the Fijis came out closer to 8,500 tons).
• Yes the 14% difference in displacement between an eight-gun Amphion and a Fiji (7,000 tons v 8,000 tons) was not big enough to justify building two separate classes and if the nine-gun Amphion did displace around 7,500 tons the argument for building only Fijis would be even greater.
• The above is similar to the argument used to only build Illustrious class carriers instead of a mix of them and the proposed trade protection ships. The Illustrious was thought to be a satisfactory design and the sketch designs for the trade protection ships weren't as they were half an Illustrious in terms of capability (half the number of aircraft and half the number of guns) but were estimated to cost 25% less than an Illustrious (£3 million v £4 million).

However, I'm suggesting that more Edinburgh class were built instead of the Fiji class and its successors. The difference in displacement between the eight-gun Amphion and an Edinburgh is about 43% (7,000 tons v 10,000 tons). That reduces to 33% for the nine-gun Amphion and an Edinburgh (7,500 tons v 10,000 tons).

 

[NOMISYRRUC]

The other caveat I have is whether its possible to actually build enough triple and twin turrets ...

Yes. My guess is that a twin 6in turret could be built in the gun pits that were used to build the twin 5.25in turrets.

• 63 of the latter were built for 14 out of 16 Dido class and the 16 extra Amphion class would require 64 twin 6in turrets so we only need one more mounting.
• Plus the 16 extra Amphions would not be competing with the King George V class for turrets (according to Naval Weapons they were given priority over the Dido class for 5.25in turrets) because I'm arming them (and Vanguard) with 4.5in guns and you want to arm them with 5.1in guns.

... and is that in itself wasteful?

No more wasteful than the "Real World" when we had the twin 5.25in gun mounting in production for the Dido class and the triple 6in gun mounting in production for the Colony class and its successors.

If anything it would be less wasteful.

• It would be easier to build 64 twin 6in turrets for 16 extra Amphion class than the 80 planned (and 63 built) twin 5.25in turrets for the 16 Dido class.
• Furthermore, it may be a different mounting to the one fitted to the Edinburgh class (that I want built instead of the Colony class and its successors) but it does use the same gun.
• Finally, the 6in gun and its twin mounting were existing designs that had been in production for some years. The 5.25in gun and its twin mounting were not.
  • Therefore, there's no time lost in re-tooling to make the new gun and its mounting.
  • So for example I think the 20 twin 6in turrets needed for the 5 Amphions that I want to be built under the 1936-37 Building Programme would have been delivered faster than the 25 twin 5.25in turrets needed for the 5 Dido class in the Real 1936-37 Building Programme.
  • This also has the advantages that as it's an existing design the teething troubles that are inevitable in a new design (i.e. the 5.25in gun and its mounting) would be avoided.

Note that what I wrote above assumes that the King George V class and Vanguard were armed with 4.5in guns in twin Mk II mountings which is what I want to happen or 5.1in guns in twin mountings which is what you want to happen.

However, I do admit that a modified Amphion armed with nine 6in guns in triple turrets would reduce pressure on the gun mounting makers as it would reduce the number of turrets required from 80 to 48 instead from 80 to 64. It would also have the tactical advantage of increasing the firepower of the forward guns by 50% and only loose 25% of the astern firepower.

These replies to your points are eerily familiar to me. I think I wrote more or less the same things earlier in the thread.

 

[Hood]

When do you think it would be ready for service?

Well the experimental 5.1in /50 QF Mark I was built in 1931.
The experimental 4in BD Mk XVIII mount was fitted to HMS Resolution for trials in 1932.
The 4.5in /45 QF Mark I entered development around 1935 and was ready by 1938.

Extrapolating from that, with the gun and turret proofed by trials by 1934 I reckon a 5.1in gun and associated BD turret could be ready for production during 1935. So there is no reason why the battleship reconstructions should not have received the gun.

Destroyers would need a different enclosed single or twin mount I suspect, maybe something like the Battle-class' BD mount or maybe something like the Mk XX as used on the L and Ms - I reckon that could be made ready for the Tribals. The added topweight might push their weight and beam up slightly, or alternatively come out as an 3x2 5.1in design with a quad pom-pom.

 

[NOMISYRRUC]

Part One of my response to Post 100.

When do you think it would be ready for service?

Well the experimental 5.1in /50 QF Mark I was built in 1931.
The experimental 4in BD Mk XVIII mount was fitted to HMS Resolution for trials in 1932.
The 4.5in /45 QF Mark I entered development around 1935 and was ready by 1938.

Extrapolating from that, with the gun and turret proofed by trials by 1934 I reckon a 5.1in gun and associated BD turret could be ready for production during 1935. So there is no reason why the battleship reconstructions should not have received the gun.

That may be the before the Point of Departure. Here's the Opening Post.

When I was looking at the blueprint of the warships before the era of Washington Naval Treaty, I suddenly thought of this.

"What if other Countries, such as United Kingdom, France, and the United States, who confirmed Japan's withdrawal from the Washington Naval Disarmament Treaty, also withdrew from the treaty at the same time?"

So I'm asking a question, what do you think happened?

On 29.12.34 in the "Real World" Japan gave two years notice that it would leave the Treaty System. Japan had to give two years notice as this was a requirement of the Washington Naval Treaty. (See Post 39 by @BlackBat242 for full details).

What I've written includes some things that I want to happen as a consequence of the Opening Post rather than what I think will happen. However, all of my changes (be they what I think will happen or what I want to happen) take place after 29.12.34.

 

[NOMISYRRUC]

Part Two of my response to Post 100.

When do you think it would be ready for service?

Well the experimental 5.1in /50 QF Mark I was built in 1931.
The experimental 4in BD Mk XVIII mount was fitted to HMS Resolution for trials in 1932.
The 4.5in /45 QF Mark I entered development around 1935 and was ready by 1938.

Extrapolating from that, with the gun and turret proofed by trials by 1934 I reckon a 5.1in gun and associated BD turret could be ready for production during 1935. So there is no reason why the battleship reconstructions should not have received the gun.

I agree.

In all you need.

• A twin 5.1in BD mounting to be built in place of the twin 5.25in and the twin 4.5in BD mounting.
• A twin 5.1in UD mounting to be built in place of the twin 4.5in UD mounting and the twin 4.7in mountings on the Tribal, Javelin & Lightning classes of destroyers.
• A single 5.1in mounting with an elevation of at least 55 degrees to be fitted to the this "version of history" versions of the Emergency Destroyer classes.
  • Hopefully, it will have a higher elevation and will also be built instead of the British Army's 4.5in AA gun.
  • Otherwise, the British Army will also have to develop a single 5.1in AA gun to be built in place of its single 4.5in AA gun.
• And in the longer term twin 5.1in mountings to be built in place of the twin 4.5" mountings on the Battle & Daring classes of destroyers & the other ships that had the Darings twin 4.5in turret and a single 5.1in gun in place of the 4.5in Mk 8.

Have you any idea what the weights of these 5.1" mountings will be? This will influence the number that can be installed in place of the "Real World's" 5.25in, 4.7in and 4.5in mountings.

My guesses are:

• Capital Ships
  • The new Capital Ships aught to be able to take ten twin 5.1in BD mountings.
    • This is because I think they'd be bigger ships than the Real-King George V & Real-Lion classes and the Real-Vanguard.
    • However, the ALT-King George V (and possibly the ALT-Lion class) may only be able to take eight of them if there's still a Second London Naval Treaty and if it still has a size limit of 35,000 tons.
  • The rebuilt Capital Ships that received ten twin 4.5in BD mountings in the "Real World" might not be able to take ten 5.1in BD mountings in this "version of history". They might not be able to take more than eight.
• Aircraft Carriers
  • One of the first ships to be fitted with the 5.1in gun would be Ark Royal.
    • She would have eight twin UD mountings in place of the eight twin 4.5in UD mountings that the Real-Ark Royal had.
    • The extra top weight may require a larger ship, but as the displacement limit for aircraft carriers was 27,000 when she was laid down and in the "Real World" had been reduced to 23,000 tons by the time she was completed (and in this "version of history" would have been left at 27,000 tons or abolished entirely) that would not be a problem.
    • Plus the larger hull required for the heavier guns might allow the ship to have wider hangars and single-deck lifts.
  • The succeeding Illustrious to Audacious classes had eight twin 4.5in BD mountings and I think larger hulls will be required to accommodate the bigger and heavier twin 5.1in BD mountings.
    • This won't be a problem legally because I expect the consequence of the OP to be no Second London Naval Treaty at all or one that is less restrictive than the real one. See above.
    • Plus I expect the ALT-Illustrious class to be built to a 27,000 ton design due to there being a less restrictive Second London Naval Treaty (or an even larger design if there was no Treaty at all) in the first place.
• Cruisers
  • As I'm expecting more Edinburgh class cruisers to be built instead of the Fiji class and it's successors.
    • The ALT-Swiftsure class might have nine 6in guns in three triple mountings and ten 5.1in guns in five twin UD mountings instead of the nine 6in guns in three triple mountings and ten 4in guns in five twin mountings that armed the Real-Swiftsure class because it used the Edinburgh class hull instead of the Fiji class hull.
    • However, the original plan for Belfast & Edinburgh class was to arm them with sixteen 6in guns in four quadruple mountings. This was changed to twelve 6in guns in four triple mountings and (if I remember correctly) the weight that saved by fitting lighter turrets was used to fit more armour.
    • In this "version of history" the Admiralty might use the weight saved to fit twelve 5.1in guns in six UD mountings in place of the twelve 4in guns in six twin mountings.
  • The ALT-Dido class.
    • If built it could have easily taken ten 5.1in in five twin BD mountings in place of the ten twin 5.25in guns.
    • Furthermore, I think the Spartan sub-class would be built with ten 5.1in in five twin BD mountings in place of eight twin 5.25in guns in four twin mountings.
    • However, it's only 25% more 5.1in guns than the ALT-Tribal class destroyers so they'll look under-armed for a ship of their size.
    • Except, I think that 16 Amphion class cruisers armed with eight 6in in four twin mountings & eight 4in guns also in four twin mountings would have been built in place of the 16 Dido class cruisers of the "Real World".
    • One could (although I wouldn't) make the the ALT-Dido class a modified Amphion (rather than a modified Arethusa) armed with sixteen 5.1in guns in eight twin BD mountings.

My response to Post 100 was to have been in a single post. However, it's gone way over time (and length) which is why I'm splitting it into three parts. Part Three will be how I think the 5.1in gun will affect destroyers.

 

[Username666]

5.1in BD mounting

What kind of weapon is BD 5.1 mounting gun? I don't know because I've never heard of it.

 

[Hood]

BD = Between Decks
UD = Upper Deck (i.e. a traditional enclosed or shielded mounting above the deck with hoist below)

Basically the turret mechanism is mounted below the level of the deck. This allowed the turret to achieve an elevation of 80 degrees without the need for a tall turret; compare the height of the BD turret with the much larger 4.5in UD Mk III mount used on HMS Ark Royal for example - a mounting also capable of 80 degree elevation but which was too large to use on destroyers). The BD turrets had greater elevation than most other British mounts of this time - 70 degrees for the 5.25in Mk I & Mk II 50 degrees for the 4.7in Mk XX on the L and M classes (note the ammunition feed did not rotate with the mounting so it was not a turret).
This reduced topweight (and made smaller targets). The drawbacks were a cramped turret given the low crown and reduced recoil space (only 18 inches compared to 26.5in for a 4.7in Mk XIX open mount) which increased stress on the ship's structure. Also the need to have larger barbette 'holes' cut into the deck compared with a traditional upper deck mount with a hoist which complicated refitting them into existing ships.

The BD Mk.IV mounts fitted to the 1942 Battle-class destroyers had a larger upper turret crown. These were superseded by the more famous UD Mk.VI of the 1943 Battles, Darings and other post-war classes.

This pic shows how low the BD turret was:

 

[Username666]

BD = Between Decks
UD = Upper Deck (i.e. a traditional enclosed or shielded mounting above the deck with hoist below)

Basically the turret mechanism is mounted below the level of the deck. This allowed the turret to achieve an elevation of 80 degrees without the need for a tall turret; compare the height of the BD turret with the much larger 4.5in UD Mk III mount used on HMS Ark Royal for example - a mounting also capable of 80 degree elevation but which was too large to use on destroyers). The BD turrets had greater elevation than most other British mounts of this time - 70 degrees for the 5.25in Mk I & Mk II 50 degrees for the 4.7in Mk XX on the L and M classes (note the ammunition feed did not rotate with the mounting so it was not a turret).
This reduced topweight (and made smaller targets). The drawbacks were a cramped turret given the low crown and reduced recoil space (only 18 inches compared to 26.5in for a 4.7in Mk XIX open mount) which increased stress on the ship's structure. Also the need to have larger barbette 'holes' cut into the deck compared with a traditional upper deck mount with a hoist which complicated refitting them into existing ships.

The BD Mk.IV mounts fitted to the 1942 Battle-class destroyers had a larger upper turret crown. These were superseded by the more famous UD Mk.VI of the 1943 Battles, Darings and other post-war classes.

This pic shows how low the BD turret was:
View attachment 700032

Thank you so much for letting me know!

 

[Volkodav]

UK yards were certainly at capacity - the splurge of Fiji and Dido class cruisers especially was filling up a lot of capacity in 1940-41.
Some brief musings on cruisers. Certainly Second London resulted in the Fijis with the 8,000 ton light cruiser limit and they were too small for what was crammed aboard them - which led to the Ceylon and Swiftsure/Minotaur classes during the war being steadily upgraded in beam and cut down in armament in order to make them more effective ships. I suspect that more Belfasts would have proved too expensive to build en-masse but another pair to help counter the Mogamis would have been likely in this scenario I would think. Indeed wartime efforts to revive the design foundered in favour of trying to make the Fiji more workable. A second batch of Gloucesters would have been likely perhaps but the numbers would have been fewer I would think simply because some Fiji slips would not have been able to handle the larger hull. I guess it might ease Dido hull congestion but gun delays hardly improve matters in that regard.

Its hard to see much real impact of a 1936 departure beyond one or two features around the overall picture. Pre-1936 offers more scope but again Britain could only do so much given the Depression effects - and even starting WW1-era cruiser and destroyer refits sooner doesn't really buy us anything additional given single 4in and basic HACS1 and shortage of pompoms etc. give much less utility and those ships would need to be refitted again to be worthy of AA duties in wartime.

For what it's worth I think a one-to-one substitution of Edinburgh class cruisers for the Colony class and its successors would have been easy.

• They were designed to have nearly the same armament (including fire control equipment) as the Edinburgh class so apart from two twin 4in mountings no change there in the cost and required production capacity.
• The Edinburghs and Colonies had 4 Admiralty 4-drum boilers feeding Parsons SR geared turbines that drove 4 shafts, but the Edinburgh class had boilers and turbines that were about 10% more powerful, that is 80,000shp v 72,500shp.
• And there's the 20% larger hull.
  • 10,260 tons standard for the Edinburgh class and 8,525 tons standard for the Fiji class (according to "Cruisers of the Royal and Commonwealth Navies" by Douglas Morris) a difference of 1,735 tons.
  • Does that mean that the hull of a Fiji class required 20% less structural steel than an Edinburgh and 20% fewer man hours were required to fabricate the hull?
  • That's not a rhetorical question, I simply don't know.

I'm a believer in the theory that "steel is cheap and air is free" and that building the Colony class and its successors instead of building more Edinburgh class ships was a false economy. I think it didn't save any money and didn't save enough labour, materials and production facilities to be worthwhile.

I too am not sure on the details back then but these days on the projects I have worked on the larger hulls are actually easier to construct and outfit than the smaller. There is better access for the workers, it is possible to undertake more concurrent activities, there is greater flexibility in arrangement, which also makes it easier to maintain stability.

 

[NOMISYRRUC]

Part Three of my response to Post 100.

It is about how I think the 5.1in gun proposed by @Hood would influence British destroyer construction.

These are the first paragraphs of Post 100.

When do you think it would be ready for service?

Well the experimental 5.1in /50 QF Mark I was built in 1931.
The experimental 4in BD Mk XVIII mount was fitted to HMS Resolution for trials in 1932.
The 4.5in /45 QF Mark I entered development around 1935 and was ready by 1938.

Extrapolating from that, with the gun and turret proofed by trials by 1934 I reckon a 5.1in gun and associated BD turret could be ready for production during 1935. So there is no reason why the battleship reconstructions should not have received the gun.

According to Naval Weapons these are the weights of the "Real World's" twin 4.5in and 4.7in gun mountings in long tons (with metric tons in brackets) in descending order of weight.

• 45.579 (46.310) twin 4.5in Mk IV on the 1942 Battle class destroyers.
• 44.000 (44.706) twin 4.5in Mk VI on the Daring class destroyers.
• 37.950 (38.560) twin 4.5in Mk II on the Illustrious class aircraft carriers.
• 37.597 (38.200) twin 4.7in Mk XX on the Lightning class destroyers.
• 29.738 (30.215) twin 4.5in Mk III on the aircraft carrier Ark Royal.
• 25.090 (25.200) twin 4.7in Mk XIX on the Tribal and Javelin class destroyers.

Notes.

• The twin 4.5in Mk III and 4.7in Mk XIX mountings had shields.
• The others were enclosed turrets.
• The twin 4.5in Mk IV & VI had Remote Power Control (RPC) and the others didn't.
• I was surprised that the twin 4.5in Mk IV was slightly heavier than the twin 4.5in Mk VI.
• I was also surprised that the twin 4.7in Mk XX was only marginally lighter than the twin 4.5in Mk II.

Quote from my Post 102.

In all you need.

• A twin 5.1in BD mounting to be built in place of the twin 5.25in and the twin 4.5in BD mounting.
• A twin 5.1in UD mounting to be built in place of the twin 4.5in UD mounting and the twin 4.7in mountings on the Tribal, Javelin & Lightning classes of destroyers.
• A single 5.1in mounting with an elevation of at least 55 degrees to be fitted to the this "version of history" versions of the Emergency Destroyer classes.
  • Hopefully, it will have a higher elevation and will also be built instead of the British Army's 4.5in AA gun.
  • Otherwise, the British Army will also have to develop a single 5.1in AA gun to be built in place of its single 4.5in AA gun.
• And in the longer term twin 5.1in mountings to be built in place of the twin 4.5" mountings on the Battle & Daring classes of destroyers & the other ships that had the Darings twin 4.5in turret and a single 5.1in gun in place of the 4.5in Mk 8.

Have you any idea what the weights of these 5.1" mountings will be? This will influence the number that can be installed in place of the "Real World's" 5.25in, 4.7in and 4.5in mountings.

This is the last paragraph of Post 100.

Destroyers would need a different enclosed single or twin mount I suspect, maybe something like the Battle-class' BD mount or maybe something like the Mk XX as used on the L and Ms - I reckon that could be made ready for the Tribals. The added topweight might push their weight and beam up slightly, or alternatively come out as an 3x2 5.1in design with a quad pom-pom.

The Real Tribal class

• In the first half of the 1930s RN wanted 70 Cruisers (25 Fleet & 45 Trade Protection).
• However, it could only build 50 ships out of the First London Naval Treaty's cruiser tonnage quota of 339,000 tons.
• Therefore, it was 20 Cruisers short of the requirement.
• The Tribal class was designed to be a Scout for the main fleets to supplement the inadequate number of Cruisers. This is why it had twice as many guns and half the number of torpedoes as the preceding A-to-I classes of Fleet Destroyer.
• The First London Naval Treaty also allowed the British Commonwealth to have 150,000 tons of Destroyers.
  • 84% (126,000 tons) could displace up to 1,500 tons.
  • 16% (24,000 tons) could displace up to 1,850 tons.
• 24,000 tons ÷ 1,850 tons = 13 Tribal class.
  • The plan was to build 7 under the 1935-36 Navy Estimates and 6 under the 1936-37 Estimates.
  • However, the Second London Naval Treaty abolished the tonnage quotas which allowed the RN to have two full flotillas of Tribals.
  • Therefore, the number built under the 1936-37 Estimates was increased from 6 to 9 and the total number of Tribals from 13 to 16.

The Alternative Tribal class

• My guess is that the RN would want the ALT-Tribal class to be armed with eight 5.1in guns in the twin UD mounting that I think will be fitted to the ALT-Ark Royal in @Hood's AU.
• The twin 4.5in Mk III weighed 4.648 tons or 18.5% more than the twin 4.7in Mk XIX.
• The twin 5.1in UD mounting will weigh more than that.
• In common with what @Hood wrote the added topweight would increase their displacement and beam.
  • However, I think it would be more than a slight increase.
  • Or as he wrote they would have to reduce the number of twin 5.1in mountings from four to three.
• Fortunately, I think it will be the former, i.e. a ship that was heavier (more than 2,000 tons) and beamier.
  • If the Treaty System does collapse completely in December 1934 (which is the what the Opening Post says happens) there is no need to keep the displacement of individual ship below 1,850 tons.
  • Plus there tonnage quotas come to an end two years earlier so there's no limit on the number of ALT-Tribal class that could be built.
• I think the ALT-Tribal class would have a hull that was the same size of the Battle class (1942).
  • The Real-Tribal was nearly the same length as the the Battle class (1942).
    • 364ft 8in at the waterline v 364ft 0in.
  • The Real-Tribal was had 3ft 9in less beam as the Battle class (1942).
    • 36ft 6in v 40ft 3in.
    • I think the ALT-Tribal would also have a beam of 40ft 3in.
  • The Real-Tribal had less powerful machinery as the Battle class.
    • 44,000shp v 50,000shp.
    • I think the ALT-Tribal class would have machinery that produced 50,000shp too.
  • However, the ALT-Tribal class would still have two funnels and a hull that was not longitudinally framed.

The Alternative Javelin class

• It would be armed with.
  • Six 5.1in in three twin UD mountings of the type fitted to the ALT-Ark Royal.
  • One quadruple 2pdr pom-pom.
  • Two quadruple 0.5in machine guns.
  • And ten 21in torpedo tubes in two quintuple mountings.
• The extra topweight meant it had to use a modified version of the ALT-Tribal class hull. The modifications were that the ALT-Javelin had a single funnel and its hull was longitudinally framed. This was effectively the Battle class (1942) hull and machinery.
• It would displace a lot more than the Real-Javelin class. However, as the Real-Javelin class was built after the Second London Naval Treaty had abolished the tonnage quotas and (sort of) raised the maximum tonnage of destroyers from 1,500 tons to 3,000 tons this would not have been a problem. And there may be no Second London Naval Treaty in this "version of history".
• It's sort of because the Second London Naval Treaty didn't have Cruisers and Destroyers. Instead it had Light Surface Vessels which were ships displacing between 100 tons and 10,000 tons. This category was subdivided into ships displacing less than 3,000 tons and ships displacing more than 3,000 tons. The former effectively replaced the Destroyer category in the First London Naval Treaty and the latter effectively replaced the Cruiser category in the previous Treaty.

The Alternative Lightning class

• If built it would be an ALT-Javelin class hull and machinery armed with six 5.1in guns in three BD twin turrets of the type fitted to the ALT-Illustrious class aircraft carriers, one quadruple 2pdr pom-pom mounting, eight 0.5in machine guns and eight 21in torpedo tubes in two quadruple mountings.
• However, I think they'd build another 16 ALT-Javelin class instead (for a total of 40) or they'd build 24 ALT-Lightning class instead of the 24 ALT-Javelin class (for a total of 40).
• There would be no need to arm some of them with twin 4in gun mountings because the reduction in the number of different gun calibres and gun mountings aught to have an economies of scale effect so the factories will be able to build more guns and mountings with the same resources.

The Alternative Emergency classes

• The Real-Emergency classes used the Real-Javelin class hull and machinery.
• The ALT-Emergency classes would have used the ALT-Javelin class hull and machinery, which as already noted was effectively the Battle class (1942) hull and machinery.
• The Real-Emergency classes were armed with four 4in, four 4.5in or four 4.7in guns in single mountings. The 4.5in and 4.7in guns could at best elevate to 55 degrees.
• All other things being equal the ALT-Emergency classes would be have been armed with four 5.1in guns in four single mountings with shields that could elevate to 80 degrees.
• However, if enough production capacity was available they would be armed with six 5.1in guns in three UD mountings or six 5.1in guns in three BD mountings as per the ALT-Javelin and ALT-Lightning classes respectively.
• The last 24 of the Real-Emergency destroyers had Remote Power Control which increased the topweight and the torpedo armament had to be halved to compensate for it.
  • I suspect that the ALT-Emergency classes would not have to sacrifice half of their torpedo armament when RPC was introduced.
  • Or as was done with the Battle class (1943) and the Battle class (RAN) they'd have their beam increased so they could have RPC and keep the the full torpedo armament.
• Post-war the many of the Real-Emergency classes were converted to Anti-Submarine Frigates. The equivalent conversions of the ALT-Emergency class would have had the same anti-submarine armament and a heavier gun armament.
  • Type 15.
    • The Real-Type 15 had one twin 4in gun mounting.
    • I think the ALT-Type 15 would be able to take one twin 5.1in BD or UD mounting (of the type fitted to the ALT-Illustrious class and ALT-Ark Royal respectively) with Remote Power Control.
  • Type 16.
    • The Real-Type 16 had one twin 4in gun mounting in B position and four 21in torpedo tubes in one quadruple mounting.
    • I think the ALT-Type 16 would be able to take two twin 5.1in BD or UD mountings (of the types fitted to the ALT-Illustrious class and ALT-Ark Royal respectively) with Remote Power Control and eight 21in torpedo tubes in two quadruple mountings.
    • Or if the ALT-Emergency classes were built with four 5.1in guns in single mountings instead of six 5.1in guns in twin mountings the ALT-Type 16 would effectively have been a more heavily armed version of the modernised C class.
      • That is:
        • Three 5.1in guns in single mountings (that could elevate to 80 degrees) with RPC in A, B and Y positions.
        • Four 40mm guns in one twin and two single mountings.
        • Eight 21in torpedo tubes in two quadruple mountings.
        • Double Squid (20 salvoes) in X position.
      • Instead of:
        • Three 4.5in guns in single mountings (that could elevate to 55 degrees) with RPC in A, B and Y positions.
        • Four 40mm guns in one twin and two single mountings.
        • Four 21in torpedo tubes in one quadruple mounting.
        • Double Squid (if I recall correctly 10 salvoes) in X position.
• Post-war the plan was to convert the 12 surviving ships of the M & N classes to Type 62 Aircraft Direction Frigates.
  • The plan was not carried out due to the cost and because the ships were too small for a satisfactory conversion.
  • However, a satisfactory conversion would have been possible in this "version of history" due to them using the Battle class (1942) hull and machinery.
  • If carried out they'd probably look like the Battle class (1943) Fleet Pickets as originally planned. Except they'd have two twin 5.1in UD or BD forward (depending upon whether they were ALT-Javelin or ALT-Lightning class) in place of the two twin 4.5in Mk IV mountings and a twin 40mm in place of the Sea Cat.

Due to the time it's taken to write this I'm not going to do the Alternative Battle, Daring & Weapon classes and in any case only the Battle class came into service before the end of the war and that was at the very end. However, I will say that as the last few classes of Emergency class destroyers were built concurrently with the Battle class more ALT-Battle class might be built instead of the last few classes of ALT-Emergency class destroyers.

 

[Volkodav]

I like your Alt Tribal.

I did an exercise a few years back and got as far as buying a kit of a Tribal plus the required accessories to build my alt Tribal. Having seen that Canada did a 4" armed Tribal and many surviving Tribals replaced the X 4.7" mount with a 4", and knowing that the original concept had five twin 4'7" mounts (Q? where the quad pompom was situated), I did some sums.

It turns out that for the weight of the four twin 4.7" and single quad pompom, you could substitute five twin 4" and two quad pompoms with weight to spare.

The inspiration was also the L class AA destroyers with four twin 4" in place of the three twin 4.7".

Arrangement would have been 4" in place of each of the 4'7"s plus a fifth mount in place of the pompom. with two quad pompoms replacing the quad .50 cals. for a Tribal AA destroyer. I don't have the calcs any more but I think the weight of fire was actually better than the 4.7" original.

An all 4" main armament reminds me of something I recall reading. The 4" had some accuracy issues, I believe due to the shell having insufficient parallel section to fully engage the rifling. If this was the case, why wasn't a new projectile designed?

 

[Colonial-Marine]

One thing about the 5.1" is to have a decent rate of fire you'd have to redesign it to use separate ammunition instead of fixed. I think you are underestimating just how much heavier these 5.1" mountings would be. Just for six guns in DP twin mountings (plus the torpedoes and light AA) you're probably looking at a destroyer larger than a Gearing class destroyer. The gun itself is going to be closer in weight to the later USN 5"/54 than the RN's 4.5" or 4.7" guns

The 4"/45 Mark XVI is said to have rather poor accuracy but ballistically the weapon's range was quite good for its caliber. Maybe they didn't want to lose that by modifying the shell design? They probably couldn't increase the overall length of the shell.

 

[NOMISYRRUC]

One thing about the 5.1" is to have a decent rate of fire you'd have to redesign it to use separate ammunition instead of fixed. I think you are underestimating just how much heavier these 5.1" mountings would be. Just for six guns in DP twin mountings (plus the torpedoes and light AA) you're probably looking at a destroyer larger than a Gearing class destroyer. The gun itself is going to be closer in weight to the later USN 5"/54 than the RN's 4.5" or 4.7" guns.

Is "you" @Hood, @Volkodav or me?

I haven't made any estimates of what the weights of the 5.1in mountings might have been.

As to the rates of fire (in rounds per gun per minute) they were going to be the same as the guns that they were built instead of:

• 14 for the 5.1in guns in single shielded mountings built instead of the:
  • Single 4.5in Mk V shielded mounting with the Mk IV gun installed on the Real Z and C classes of destroyer.
  • Single 4.7in Mk XVIII shielded mounting with the Mk IX gun installed on the Real O & R classes of destroyer.
  • Single 4.7in Mk XXII shielded mounting with the Mk IX gun installed on the S, T, U, V, W and Battle (1943) classes of destroyer.
• 12 for the 5.1in guns in twin shielded mountings built instead of the:
  • Twin 4.5in Mk III shielded mounting with Mk I & III guns installed on the Real Ark Royal, two Dido class and some auxiliaries.
  • Twin 4.7in Mk XIX shielded mounting with Mk XII guns installed on the Real Javelin and Tribal classes.
• 12 for the 5.1in guns in twin turrets built instead of the:
  • Twin 4.5in Mk II turret with Mk I & III guns installed on the Real Illustrious class and the Real rebuilt Queen Elisabeth, Renown & Valiant.
  • Twin 4.7in Mk XX turret with Mk XI guns installed on the the Real Lightning class.
  • Twin 5.25in Mk I & II turrets with Mk I guns installed on the Real Dido, King George V, (original) Lion and Vanguard classes.
• 15 to 20 for the 5.1in guns in twin turrets built instead of the twin Mk IV turret with Mk I & III guns installed on the Real Battle (1942 & 1943) classes.
• 24 for the 5.1in guns in twin turrets built instead of the twin 4.5in Mk VI & VII turrets with Mk V guns installed on the Real Battle (RAN), Daring, Malta & Lion (1945) classes.

Rates of fire are according to the Naval Weapons website.

The 4"/45 Mark XVI is said to have rather poor accuracy but ballistically the weapon's range was quite good for its calibre. Maybe they didn't want to lose that by modifying the shell design? They probably couldn't increase the overall length of the shell.

I don't see how that's relevant because I'm keeping the 4in gun its twin mounting as they were and as far as I know so was @Hood. Please explain. I'm not being sarcastic. I simply don't understand.

 

[Volkodav]

One thing about the 5.1" is to have a decent rate of fire you'd have to redesign it to use separate ammunition instead of fixed. I think you are underestimating just how much heavier these 5.1" mountings would be. Just for six guns in DP twin mountings (plus the torpedoes and light AA) you're probably looking at a destroyer larger than a Gearing class destroyer. The gun itself is going to be closer in weight to the later USN 5"/54 than the RN's 4.5" or 4.7" guns.

Is "you" @Hood, @Volkodav or me?

I haven't made any estimates of what the weights of the 5.1in mountings might have been.

As to the rates of fire (in rounds per gun per minute) they were going to be the same as the guns that they were built instead of:

• 14 for the 5.1in guns in single shielded mountings built instead of the:
  • Single 4.5in Mk V shielded mounting with the Mk IV gun installed on the Real Z and C classes of destroyer.
  • Single 4.7in Mk XVIII shielded mounting with the Mk IX gun installed on the Real O & R classes of destroyer.
  • Single 4.7in Mk XXII shielded mounting with the Mk IX gun installed on the S, T, U, V, W and Battle (1943) classes of destroyer.
• 12 for the 5.1in guns in twin shielded mountings built instead of the:
  • Twin 4.5in Mk III shielded mounting with Mk I & III guns installed on the Real Ark Royal, two Dido class and some auxiliaries.
  • Twin 4.7in Mk XIX shielded mounting with Mk XII guns installed on the Real Javelin and Tribal classes.
• 12 for the 5.1in guns in twin turrets built instead of the:
  • Twin 4.5in Mk II turret with Mk I & III guns installed on the Real Illustrious class and the Real rebuilt Queen Elisabeth, Renown & Valiant.
  • Twin 4.7in Mk XX turret with Mk XI guns installed on the the Real Lightning class.
  • Twin 5.25in Mk I & II turrets with Mk I guns installed on the Real Dido, King George V, (original) Lion and Vanguard classes.
• 15 to 20 for the 5.1in guns in twin turrets built instead of the twin Mk IV turret with Mk I & III guns installed on the Real Battle (1942 & 1943) classes.
• 24 for the 5.1in guns in twin turrets built instead of the twin 4.5in Mk VI & VII turrets with Mk V guns installed on the Real Battle (RAN), Daring, Malta & Lion (1945) classes.

Rates of fire are according to the Naval Weapons website.

The 4"/45 Mark XVI is said to have rather poor accuracy but ballistically the weapon's range was quite good for its calibre. Maybe they didn't want to lose that by modifying the shell design? They probably couldn't increase the overall length of the shell.

I don't see how that's relevant because I'm keeping the 4in gun its twin mounting as they were and as far as I know so was @Hood. Please explain. I'm not being sarcastic. I simply don't understand.

I believe this was in response to my post.

The section referencing the 4" definitely was. I was querying something I read some time ago referencing the poor accuracy of the 4" and suggesting it was due to insufficient parallel section of the actual projectile meaning it didn't fully engage the rifling.

 

[Hood]

I've not crossed the ammunition hurdle yet - such as it is.
The Admiralty rejected the 108lb 5.1in projectile as too heavy for manual loading on a destroyer. Later shells were 62lb instead of 70lb in order to reduce this to around 100lb.

The 4.5in was selected as the largest calibre that could have a manually-handled fixed projectile of 85lb (actually it came out at 87lb).
This does seem odd though because 4.7in ammunition used a separate shell and cartridge to reduce loading workload on destroyers and in the 1920s a fixed projectile had been developed for the 4.7in L/40 Mk.XII aboard the Nelsons which came in at 74lb but it had reduced RoF as loaders quickly tired and it was deemed too heavy. So why if by the early 1930s 74lb was deemed too heavy for a fixed-projectile were the Admiralty by the mid-1930s wanting an 85lb fixed projectile! (Note the 5.1in was mainly intended as a surface weapon on a modified 4.7in CP XIV mount with 40 degrees elevation).

During the war the 4.5in didn't have a good rate of fire either and often during loading the projectiles separated from the cartridge cases which also slowed the loading process. So yes, for my money I would go with split ammunition - it wasn't feasible to develop a high-angle AA gun with a calibre over 4in with fixed ammunition and the Admiralty should really have figured this out.

 

[lancer21]

Is there room for a bit more IJN love here? Given the discussion about guns and cruisers above, i was thinking of realistic ways to improve japanese cruisers and DD guns at least from the OP POD of 1934. What changes would be needed for the 15,5cm/60 gun to equal or at least almost match (let's say 7-9 rpm) the firing rate of the US 6 in/47 (8-10rpm), how did the americans achieved suh a high rate of fire?

I did also note that the japanese gun is twice as heavy as the US one, 12 tons vs just 6, however it's an L/60 of course (presumably because of the outranging the enemy strategy). Could the japanese gun made somewhat lighter, or it needs to be a new design, say an L/55, and incorporating whatever features the US gun has to achieve a high ROF within an acceptable turret weight?

Same for destroyer guns, how about a japanese true DP 12,7cm gun with good training and elevation speed and decent ROF (say 12-18 rpm), not quite like the US 5in/38 at 15-22 rpm, but close enough. I note the US gun has power ramming which it's said to greatly help with the ROF and loading at any angle. The japanese DID design a DP 12,7cm/50 gun, the Type 1/5, but it was way too late and also heavy, i think i read somewhere a twin turret/mounting would have been 48 tons, compared to 33 tons for the normal SP 12,7cm/50 mountings on the japanese DDs. Does this new DP destroyer gun needs to be say an L/45 weapon to help reduce weight?

 

[lancer21]

As to the cruisers themselves, focusing on an IJN cruiser ATL, just managing to build the planned 4 or 5 Aganos, 2 Oyodos and 2 Ibukis would be something. By comparison the US and UK built an obscene amount of cruisers during the war.

My favourite Peter to rob are the Katoris, based on what i can gather on the Yokohama shipyard, it had one slip able to take at least an 179 metres ship (see Ryujo), and another one at least 163 metres long (see Hikawa-Maru class). My idea is to build only 2 training cruisers from 1938, but larger and much more combat capable, something like the french Jeanne D'Arc. So either 2 ships of say 160 metres length, 6x14 cm guns, 2x 12 or 12,7cm AA guns and 6-8 TT, machinery like Chitose class (turbines and diesels) and a speed of 27 kts or so, OR one larger 175 metres ship and one smaller 160 metres long (to stay within drydock limits). Then once these two are launched, one Agano class to be built which at 174 metres long would fit nicely, say the Noshiro.

At Yokosuka then, instead of the Noshiro, IF the drydock is hopefully long enough, as i'm not quite sure in which dock it was built, but i strongly suspect it was no. 4 which in 1940 was about 213 metres long, so an easy fit, i would have the Niyodo built there.

As to the Ibukis, If an Unryu is built instead of Junyo and is launched say summer 1940, then that leaves loads of time and space to start the Ibuki say one year early or even more, like late 1940 (the shipbuilding programs may need to be altered for this to happen, but as i understand they wanted 2 CAs under Maru 3 anyway, but had to give up because there was no space, only to revive them in the 1941 war-emergency program). Kurama could then follow it, though probably it will have to be finished in 1944.

There could be of course other permutations to get to the scenario i'm after.