A Slightly Different Second London Naval Treaty

We seem to of had a spate of aircraft carrier threads lately and they got me thinking, never a good idea. :) With previous naval treaties nations had been limited to carriers with a maximum standard displacement of 27,000 tons and a maximum total standard tonnage per navy - 135,000 tons each for Britain and the US, 81,000 tons for Japan, and 60,000 tons each for France and Italy. By the time of the conclusion of the Second London Naval Treaty in 1936 however this had changed with the maximum total tonnage displacement for carriers having been scrapped and the maximum displacement for each carrier reduced to 23,000 tons. This is illustrated in the Royal Navy by all of the carriers laid down in the years before WWII having kept to the 23,000 ton limit only increasing with the Audacious-class at 36,800 tons after the war had started.

So what if the individual maximum displacement were slightly higher than our timeline's by 2,000 tons at 25,000 tons? The British negotiators apparently wanted to make it even lower at 22,000 tons but had to give way when other nations at the conference objected and accept the extra 1,000 tons maximum displacement. For the sake of this thread assume that people objected even more strenuously and the British negotiators felt that they had to accept a larger maximum displacement of what turned out to be half way between our timeline's agreed upon figure and the old one. What do people think the various navies would do with an extra 2,000 tons in hand to play with - simply slightly heavier variants of our timeline's carriers or something radically different?
 
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Saphroneth

Banned
Well, the first thing to say is that in a tonnage limited design an extra 2,000 tonnes can get you a lot.

Let's look at the Ark Royal. Her flight deck area is 800 feet by 95 feet (approx) coming to about 6,840 square metres.

Now, 3" of steel (the armour thickness on the Illustrious) is 7.5 cm, which is 0.075m, and the density of steel is about 8 tons per cubic metre.

So 3" of steel on the flight deck is 4,000 tonnes. This is ballpark of the increase from Ark Royal (22,000 tonnes) to this 25,000 tonnes limit.

What I think that means is that, with the kind of weight saving you see on Illustrious, you could get an armoured carrier with capabilities closer to that of Ark Royal than that of Illustrious.


Seems like the best of both worlds to me - enough aircraft that more would be hard to control, and the armour to stop a 1,000 kg bomb without sinking the ship.
 
First cuts is that you end up with a ship more like the later 2 armoured carriers, which were over 22k.

The ship would have 4 shafts, better protection and probably 10% more aircraft. They may well have gone for the 1 1/2 hanger solution.

10% extra tonnage gets you about a 20% better ship, at the limits.
 

NoMommsen

Donor
The British negotiators apparently wanted to make it even lower at 22,000 tons ...
Weren't they starting with something even lower ? ... about 18,000 tons ?

For exlpoiting the "lowest possible" they build the HMS Hermes
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and the japanes tried the same with the ILN Ryujo
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wich both were planned around only 10,000 tons.
The high tonnage of the previous treaties were afaik due to the carriers of that time being converted Battelcruisers, that came already with a VERY high tonnage.
...
...
... or am I at the wrong conference :eek: ?
 
I thought there was an 'escalator clause' in 2LNT that carriers were to be 22kT but if a non signatory went above that limit signatories could build to 27kT. This is why the Essex and the Indomitable (not sure, the pair of 4 shaft armoured hangar carriers finished in 1944) were 27kT but earlier carriers were 20-22kT.
 
10% extra tonnage gets you about a 20% better ship, at the limits.
Right, wasn't sure if it would be a case of a 13% increase in tonnage would result in a 13% 'better' design or whether it would be non-linear in either a smaller or larger improvement than that.


Weren't they starting with something even lower... about 18,000 tons?
That does ring a bell somewhere.


For exploiting the "lowest possible" they built HMS Hermes.
I'm having to rely on the internet at the moment as no books to hand but Hermes looks to have been launched a little over two years before the Washington Naval Conference started, even though it wasn't finished fitting out and commissioned until a couple of years after it was signed, so I'm not sure how much of that was intentionally going for as low a displacement as possible and how much it simply being the first purpose-designed carrier before they started growing.


Which both were planned around only 10,000 tons.
IIRC they couldn't go lower than that since one of the conferences, I think it was First London, actually set a minimum displacement for aircraft carriers. This is going from very hazy memory though.


I thought there was an 'escalator clause' in 2LNT that carriers were to be 22kT but if a non signatory went above that limit signatories could build to 27kT. This is why the Essex and the Indomitable (not sure, the pair of 4 shaft armoured hangar carriers finished in 1944) were 27kT but earlier carriers were 20-22kT.
Again I'm having to rely on online sources but most of them seem to have the Illustrious-class at 23,000 tons standard displacement and 29,700 tons loaded. The follow-on Implacable-class seem to have been roughly the same at 23,500 tons with the first major increase being the Audacious-class jumping up to 36,800 tons. The 'finished in 1944' bit sounds as though you're thinking of the Implacable-class.
 
You're right, 30% more power, an extra shaft, more hangar and fuel as squeezed into 550 tons light but the deep load went up from 29,000 tons to 32,000 tons which is what I must have been thinking of. The jump to Audacious was huge.
 
So what if the Implacables were designed to 27kT instead of 23kT? IIUC half of the bottom hanger was used for personnel accomodaton and other non aviation stuff because the extra crew needed to run the extra machinery weren't properly accomodated for in the 'small' design.
 

Saphroneth

Banned
So what if the Implacables were designed to 27kT instead of 23kT? IIUC half of the bottom hanger was used for personnel accomodaton and other non aviation stuff because the extra crew needed to run the extra machinery weren't properly accomodated for in the 'small' design.

Well, I know that by the time you reach the air capacity of the Essex class - with WW2 aircraft sizes - you're getting to the limit of what you can feasibly control. Given that early WW2 aircraft were smaller than late WW2 aircraft, I think a 27,000 T carrier would be more all-round if it were armoured. (The bonus is that the British design concept also includes a Unicorn-class armoured carrier, and those were amazing ships - not much fighting capacity, but true carriers and with lots of workshops on board. Three 27kt Implacables and a 20kt Unicorn would be a combined weapons system capable of fighting perhaps 280+ aircraft (80+ per Implacable, 40 for the Unicorn) and with significant aircraft retention capabilities in case of damage. (Implacable could operate 81 aircraft, though couldn't handle late-WW2 large ones - a 27kt version would presumably have higher hangars)

If you have Unicorn be a full 27kt, you have something pretty special.

The other benefit of 27kt instead of 23kt is that you have a little more room for growth of the ancillaries (like radar or AA guns).
 
Something that was noted in the WTRE exercise regarding the OTL Illustrious class




i. One of the weight saving concepts which lead to this was that the armour plate was used both for protection and longitudinal strength. No backing was used for the armour. The 3” flight deck armour and 4½” hangar side armour was worked structurally with riveted and rabbited laps and butts.
ii. The armour was thus the load girder, both horizontally (the deck) and vertically (the hangar walls). This lack of specific structural support for the armour was the design weakness in the armoured carrier. But without the limitations on displacement, the armoured box becomes simply an armoured box mounted upon structural supports, not an-inverted U-shaped girder. If the Illustrious class had been built to a displacement limit of say, 24,500 tons, they would probably not have had the structural problems resulting from heavy bomb hits, because the armour would have had structural backing.
 

Saphroneth

Banned
I think the structural problems in the armoured carriers are a little exaggerated, myself - they lasted on the same order as long as other carriers of the same vintage, despite being worked much harder. (I mean, sure, Illustrious was never quite the same, but that many bombs would have sunk any two other carriers and she carried on until 1955.)
 
You're right, 30% more power, an extra shaft, more hangar and fuel as squeezed into 550 tons light but the deep load went up from 29,000 tons to 32,000 tons which is what I must have been thinking of. The jump to Audacious was huge.
[SNIP]

If the Illustrious class had been built to a displacement limit of say, 24,500 tons, they would probably not have had the structural problems resulting from heavy bomb hits, because the armour would have had structural backing.
These two posts raise the interesting idea of an Illustrious-class that's effectively built as our timeline's following Implacable-class with their improvements - extra shaft, installed horsepower, hangar and fuel - and an armour scheme that doesn't also have to act as part of the structural support of the ship. I've got no idea how possible that might be without the experience of operating our timeline's Illustrious-class and how that filtered into the Implacable-class design though. Assuming for a moment that it did happen then that in turn could see a jump up to a much larger Audacious-class type carrier in 1939 rather than 1942.
 
These two posts raise the interesting idea of an Illustrious-class that's effectively built as our timeline's following Implacable-class with their improvements - extra shaft, installed horsepower, hangar and fuel - and an armour scheme that doesn't also have to act as part of the structural support of the ship. I've got no idea how possible that might be without the experience of operating our timeline's Illustrious-class and how that filtered into the Implacable-class design though. Assuming for a moment that it did happen then that in turn could see a jump up to a much larger Audacious-class type carrier in 1939 rather than 1942.

Well as far as I can see, the treaties were worse off than parrots by the time the Implacables were designed and laid down so why any attempt was made to keep them within the limits I don't see.
 

Saphroneth

Banned
Well as far as I can see, the treaties were worse off than parrots by the time the Implacables were designed and laid down so why any attempt was made to keep them within the limits I don't see.
I think it's because they felt in 1938 it was still (just) possible to de-escalate things. And by the time they were laid down, it was a good few months too late to design a 25kt or 28kt carrier.
 
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