When is your POD?
I dont think 15" works as USN/IJN only have 14" or 16" and if you can have 15" then you can go to 16" and potentially breach the 35kt limit....
I think 27 Kn is also to slow you really want,
2x 14" quad forward
8x twin 4.5" (with split loading)
lots of light 40mm AA
protection as KVG (maybe with more TDS on rear shafts & more none turbo pumps if you have a crystal ball)
as much speed as you can 28-30+.... (this is a big deal to catch raiders S&G or B&T)
Don't know what POD is, but the idea is to have ships operational at the same time or even earlier than OTL King George V design. So basically you already have good 15' guns, so all you need is design turrets for them. Or, alternatively, you can design entirely new guns, but still have the advantage of already having ammunition stocks and production lines.
I used 27 kts to be conservative, but I do believe that even with 2 x quad 15'' ships could go at least 30 kts. This is the original KGV stats:
- 227 m overall length
- 31,5 m beam
- 10 x 14 in main armament (1 590 lbs projectile; 15 900 lbs broadside)
- 14,7 in belt armour
- 5 in deck armour
- 12,75 in turret face
- 28,3 kts speed
- 35 000 t standard displacement (36 750 t)
Richelieu stats:
- 248 m overall length
- 33,1 m beam
- 8 x 15 in main armament (1 950 lbs projectile; 15 600 lbs broadside)
- 12,9 in belt armour (inclined)
- 6,7 in deck armour
- 17 in turret face
- 32 kts speed
- 37 250 t standard displacement
Now, using quad 15'' in two forward turrets:
- BL 14'' Mk.VII is 16,31 m bore length; 380 mm/45 modele 1935 is 17,26 m barrel length
- BL 14'' Mk.VII weight 78,99 t; 380 mm/45 modele 1935 weight 94,13 t
- KGV turret weight: 1 582 t quad, 915 t dual; Richelieu quad turret weight: 2 274 t
- Total turret weight: 4 079 t KGV, 4 548 t Richelieu
Thus 15 in guns if copied from Richelieu should have following stats:
- 8 x 15 in main armament (1 950 lbs projectile; 15 600 lbs broadside)
- Turret weight: 2 274 t
- Total turret weight: 4 548 t
Using grandmother's dentals a.k.a. Vanguard would result in 1 938 lbs projectile and 15 504 lbs broadside (97,5% of OTL), but also much quicker build process.
Removing the aft turret while replacing dual turret with quad mount and also increasing calibre to 15'' should result in:
- belt armour weight reduction to 95% of original (used Rule The Waves ship designer for this)
- deck armour weight reduction to 95% of original
- assuming all armour reduction is 95% (turret armour was counted under "armaments weight"), armour weight savings are 621 t (12 413 t to 11 792 t)
- hull if reduced also may be reduced in weight by 692 t (13 830 t to 13 138 t)
- main turrets weight increase is 469 t (4 079 t to 4 548 t)
- OVERALL: weight reduction by 844 t
- 844 t is 6,8% of KGV's armour weight; if applied to thickness equally, 6,8% increase would increase belt armour from 14,7 in to 15,7 in, deck armour from 5 in to 5,3 in and turret face from 12,75 to 13,62 in. Alternatively, and more usefully, 844 t would allow for installation of additional 48 pom-poms (which would add 384 barrels to ship's AAA suite - probably not physically possible due to space restructions).
They're not laid down till 1937 due to the treaties. War is extremely likely either against Germany or Japan. Lie about the tonnage to get the ship you want.
The entire idea is to get maximum out of allowable tonnage, so I wouldn't go that route.
The idea that going 14" caused all sorts of problems largely is a myth - there were delays imparted on the KGVs but my understanding is this is mostly to do with changing the B turret from a 4 gun to a 2 gun turret in order to increase armour and stability worries that the much heavier 4 gun turret would have riding as it would have been higher up in the hull.
Whatever gun they decided on it was going to have all of the same safety features, anti flash etc built into it as the 14" system generating teething issues that would need to be overcome and obliged to shoehorn it into a limited hull size and tonnage as the 14" system.
I am aware of that. 14'' gun itself was a very good design; it was flash protection system that was too complex. The idea here is to use 15'' guns to a) get more firepower for tonnage or protection for tonnage/firepower (keep up broadside weight while going one turret down) and b) potentially reduce design time, build time, or
both, as guns are one of most important long-lead items. Using 15'' guns would (theoretically) allow to build turrets with preexisting 15'' guns, and then swap those guns with more modern variants as they became available.
As to what happened - well the expected 2nd London Naval treaty was expected to limit gun sizes to 14" and while the US waited for the escalator clause to allow them to go up to 16" the British pressed on deciding that it was better to start building them now and having modern battleships in service earlier and then to build 16" armed ships later if needed (with 2 laid down in 1939)
After all they had a block obsolescence problem with 10 old Battleships (all built between 1913 and 1915) and 3 old Battle-cruisers all them pre-Jutland and only 2 post Jutland Battleships (NelRod).
At the time of making the decision the following was going on.....
Germany had 4 modern fast battleships building or planned
Italy had started building 2 modern fast Battleships and planned to build 2 more
Japan had modernised or were modernising all 10 of its battleships
So Britain had to do something then rather than later and had to hedge its bets on the 2nd LNT
At the end of the day there is nothing the KGVs did that could have been done better by another treaty battleship and given that Battleships were found increasingly 'wanting' in the face of modern air-power any extra resources used on them would have been squandered.
Part of the idea here is to get ships designed and into service as quickly as possible by using old 15'' guns which would then be swapped with more modern variants as they became available. I believe it was precisely guns and turrets which were limiting factor in British battleship building capacity - hence the Vanguard. And Brits had awful lot of ancient 15'' guns lying around from all pre-World War I ships that were scrapped due to treaties, so... of course, turrets themselves would still need to be built, but if you used 2x2 setup (essentially, two twin mountings side-by-side) it might - in theory - be possible to even reuse whole mechanism, not just guns.
Regarding 5" guns - there were no 5" guns in British service - a 5.1" had been under development but was abandoned due to ammunition weight issues
The
twin 4.5s would have been the best answer
I understand why Britain went 5.25" - Aircraft were operating from increasingly higher altitudes requiring larger guns and a larger warhead as well as Torpedo ranges were now to the horizon requiring a secondary gun system capable of reaching out to that range capable of damaging Destroyers and Crusiers.
Wasn't the OTL-Admiralty's originally preferred design a 3x3 15-in plus the rest as was built OTL anyway?
I found something to that effect but never any details.