American militarism pre-WW2 and the Ultimate Battleship

[Terry Duncan]

Hello All :

Since you are just face hardening the steel, you can always take a sheet of 6" thick STS steel, face harden it, and then secure it to an 18" thick sheet of HTS steel by dovetailing the backside of the face hardened sheet and the frontside of the HTS sheet and then slotting them together, to form a single sheet of armour. This is referred to as 'compound armour, and is much used today on a variety of armoured vehicles.

In fact, you could dovetail both sides of four sheets of 2" STS, and four sheets of 4" HTS, face harden the STS, and then assemble them into a sandwich of 24 inches of alternating face hardened and High Tensile Steel to give you a similar effect to what is known as ' Chobham Armour ' .

Mr. Duncan, in my experience as an Engineer, I have learned that there are over 40 ways to skin a cat, and only 13 of them require the use of a knife....


Respectfully :

Paul R. Ward

Yes, you could do all of these ideas above, and achieve a less resistant belt than the 24" the OP suggested. It certainly would not have the benefits of Chobham, which were mostly concerned with reducing the effectiveness of HEAT rounds, and where weight was somewhat less of a problem than in a ship as even a tank like the Chieftan with all its mobility issues tends not to turn over or sink. Of course, if the OP is happy with an effective thickness of 18" or 20" then multiple plates or even a belt of standard steel are possible.

[Takao]

The P-51 was rejected because it was found:

To have a poor view of the deck on approach.
A very narrow speed window for landing that would make it a difficult plane to land for average pilots.
The landing gear rebounded too much.

Arghhhh... It doesn't need to be the P-51 specifically, though each of these demerits would be diminished in the presence of a landing deck 3x longer and wider.

The point isn't about the P-51 or B-25 or He-177 or Lancaster specifically!
It's that a much-larger deck would enable operation of larger, more capable planes.
Does anyone disagree with that?

I believe I said "for example" the P51/A26 or "something like" it.

It's a bit frustrating when folks refuse to see a forest because they're arguing about what kinds of trees are there.

As has been said, larger does not necessarily mean more capable. You could say that the smaller Skyraider was more capable than the larger Mitchell. O

Also, the size of the air group could be too large to be efficiently used, as was such on the newly commissioned USS Midway.

Its going to require a lot of elevators to make the design efficient, which will mean a lot of holes in your strength deck. They will also need to move a lot more weight, while maintaining a fast cycle time. Further, while you have more space, you also have larger aircraft to move, so it's not as if you can add more elevators.

[T. A. Gardner]

Look, on the armor issue we could go round and round on that for weeks. My personal rule of thumb is that when the armor gets over about 3" thick, what sort of heat treatment or face hardening it has really doesn't mean much. What counts is the exact alloying of it for toughness and ability to undergo deformation. Today, that would normally be the ASM 86XX series steels, among others. These are also often called "Triple alloy" steels.
The other critical factor is controlling grain size during cooling. Smaller and more uniform grains in the steel (the crystallization pattern) makes for a much tougher plate.
In the 1930's and 40's this was harder to achieve on a mass production basis than it is today.

As for aircraft: Two big factors on a carrier, of any size, are going to be the space the plane takes up on deck or on an elevator. A B-25 can't be struck down to the hanger of an Essex class carrier. The elevators are too small and the weight of the plane exceeds the limit of the elevator.
Thus, for any carrier you have to consider the weight and size of the plane when it's in its non-flight / stored condition.
Also, many aircraft not designed for carrier use are not really suitable for carrier use. Like the P-51, if the plane has characteristics that make it a poor carrier plane (like the Seafire / Spitfire) then yes, you might use it aboard carriers in a pinch but expect higher non-combat losses, more maintenance on it, and generally it being less desirable for use.

Also, there's take off's. The length of the take off run, loaded has to be considered. How much deck space does that take? If you use catapults, then you need to modify the plane so it can use them, and have a catapult that can handle the weight of the plane and get the necessary acceleration to get it airborne. In the late 1930's for the USN that would be using a hydraulic catapult. Steam cats like in use today, didn't exist yet.

As I said earlier, and Takao reiterated, just because you have the space doesn't make it efficient or desirable.

[TheMarcksPlan]

As I said earlier, and Takao reiterated, just because you have the space doesn't make it efficient or desirable.

I know it might feel good and wise to utter proverbs like this but stop for a moment and think about the argument it formally addresses.
As a matter of syllogistic logic, you're responding to a contention "anything for which one has space is efficient and desirable."

Have I said anything like that? No, of course not.

Rather, I've listed several discrete benefits of operating larger aircraft from carriers.

If it turned out that NONE of the larger existing planes could operate from carriers then fine, probably don't convert one of the MegaBB's to a MegaCV.

But one can't reasonably deny that operation of longer-range and more capable aircraft is a reason (not necessarily a decisive one) to consider a MegaCV.

As so often on this forum, folks get tied up in knots on particulars and are blind to the broader strategic issue.

Also, there's take off's. The length of the take off run, loaded has to be considered. How much deck space does that take?

Of course it has to be considered! That's the entire reason that a MegaCV might offer worthwhile benefits! It has a longer runway for larger planes [and hangar space for them]!
Re the exact takeoff run required for a loaded A-26 or whatever - I don't know. Anyone have those figures?

[paulrward]

Hello All :

In # 194, Mr. TheMarcksPlan posted :

There are many members - some in this thread - who claim to despise alternate history,
yet whose most active forum is always "What If."

and

Our friendly pal....... is always posting about "what was" in "what if." Best not to engage
in these contretemps,

Here is something for all posters in the What If Forum to consider:


Some men see the World the way it is, and ask " Why ? "

Other men see the World the way it could be, and ask, " Why NOT ? "

This thread is for those who can look at the World the way it WAS, and ask, " WHAT IF ? "


I have been an engineer for most of my career. My job, my profession, is to find creative solutions to real world problems. Like the Mission Control personnel in the film Apollo 13, " Failure is NOT an option ! " I have developed
new or improved production and quality control techniques, streamlined manufacturing processes, and improved profitability at EVERY firm I have ever worked for. That was MY JOB !

If you were in any engineering department in the Silicon Valley, where I spent my career, and, when you were presented with a problem, your response was to say, " It can't be fixed....It can't be done.... Nobody has ever done that before.... It isn't the way things were done in the past..... ", you would very shortly be looking for a new place of employment.


Award winning author and Futurist Arthur C. Clarke had three Laws which apply to this forum:

1. When a distinguished but elderly scientist states that something is impossible, he is very probably wrong.

2. The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

3. Any sufficiently advanced technology is indistinguishable from magic.


What we have to be careful of is what was postulated as a potential fourth law by J. Porter Clark:

4. Any sufficiently advanced cluelessness is indistinguishable from malice.


However, if you can master the process of seeing the world the way it used to be, and asking " What If ', and come up with valid ideas, then it is only one short step from seeing the world the way you want it to be, and saying, " This is how we go about making it happen ! "


As one of the Twentieth Century's greatest innovators once said to a very wealthy business executive, " Look, you have a choice: You can stay here and sell colored sugar water to children for the rest of your life, or you can come out to California with me and Change the World ! "

Respectfully :

Paul R. Ward

[TheMarcksPlan]

Of course, if the OP is happy with an effective thickness of 18" or 20" then multiple plates or even a belt of standard steel are possible.

Are you saying that you couldn't fashion a 24in Class B plate? Okhun's material on Navweaps doesn't specify an upper bound for thickness; I haven't seen one elsewhere either.

I'd want to armor this ship against penetration full stop - I wouldn't be worried about breaking up oblique shells with Class A armor.

My target for deck armor protection would immunity at any range from ~21in "super heavy" shells. Per the USN penetration formula, Iowa's shells could penetrate 14in at max range. Assuming roughly quadratic relationship between shell caliber and penetration, 24in deck armor gives immunity to 21in shells at max range.

[TheMarcksPlan]

What we have to be careful of is what was postulated as a potential fourth law by J. Porter Clark:

4. Any sufficiently advanced cluelessness is indistinguishable from malice.

Now that is a great quote!

[Terry Duncan]

Of course, if the OP is happy with an effective thickness of 18" or 20" then multiple plates or even a belt of standard steel are possible.

Are you saying that you couldn't fashion a 24in Class B plate? Okhun's material on Navweaps doesn't specify an upper bound for thickness; I haven't seen one elsewhere either.

I'd want to armor this ship against penetration full stop - I wouldn't be worried about breaking up oblique shells with Class A armor.

My target for deck armor protection would immunity at any range from ~21in "super heavy" shells. Per the USN penetration formula, Iowa's shells could penetrate 14in at max range. Assuming roughly quadratic relationship between shell caliber and penetration, 24in deck armor gives immunity to 21in shells at max range.

You could use Class B armour, it is just not as effective. Typically the belt would be made of such armour because of the threat posed by shells that penetrated intact and then exploded. As I said, you can use a lot of options, but I cannot second guess them.

You want protections vs 21" shells at any range? OK. What weight for the shell? I wouldnt worry about 'super heavy shells' as they had a tendency to deform on impact if the angle was too oblique, the British rejected them for this reason as too high a percentage would deform and fail entirely. I think you may be suprised at the thickness of armour needed at under 5k yards to resists such a large shell.

[TheMarcksPlan]

The program will break down weights, but it is also dependent on what details are put in. For example, what depth is your 24" belt? Given the variable draught hull idea, it is going to have to cover at least the waterline at deep load, but will it still cover it at light load? There is a lot of difference in a belt 12' deep to one 40' deep. The hull still has to cope with the belt weight for stability purposes at both load conditions.

Forgot to answer this. For the 2400x360ft MegaBB, the belt is 50ft deep. That covers our 40ft of freeboard and 10ft below the waterline.

To continue our discussion of class A/B armor, I'm not that concerned about the belt armor with this ship. A few points:

1. The armored belt would be behind ~20ft of void that would be water-filled in battle conditions. Therefore any shell is significantly slowed or exploded before it strikes.

2. Battle tactics for this ship would be to maintain at least 25,000 yards range. It's hard to punch a hole in armor belt at those ranges even absent 20ft of water. With this ship being faster than any BB and as fast as all but the fastest DD's, it can dictate tactical range. With 90% of its armor behind the superstructure, it can fire over the shoulder or on the run while maintaining range separation. Plus the MegaBB's Mega-ConningTower (~300ft above waterline) means a ~70mile horizon for radar and good-day visual. Keeping range at ~30k yards means no hits from secondary/cruiser armament, while the MegaBB can sink 100 BB's with 1% accuracy before running out of ammo.

[TheMarcksPlan]

You could use Class B armour, it is just not as effective. Typically the belt would be made of such armour because of the threat posed by shells that penetrated intact and then exploded. As I said, you can use a lot of options, but I cannot second guess them.

You want protections vs 21" shells at any range? OK. What weight for the shell? I wouldnt worry about 'super heavy shells' as they had a tendency to deform on impact if the angle was too oblique, the British rejected them for this reason as too high a percentage would deform and fail entirely. I think you may be suprised at the thickness of armour needed at under 5k yards to resists such a large shell.

Our last posts crossed each other in the night like Scheer over Jellicoe's wake...

I want ONLY THE DECK protected at every range.

The 21in Super Heavy would weigh 6,100lbs by cubic escalation from 16in shells.

Like I said in my last post, I'm not that worried about close-range shots. If an enemy somehow survives to get within range to penetrate 24in of Class B armor it'd be either a miracle or a ship at least as big as the MegaBB - which means Japan/Germany has built nothing else.

[TheMarcksPlan]

I want ONLY THE DECK protected at every range.

This points up a drawback to the MegaBB design: With such a giant hull you have a huge target for long-range plunging shells. You'd never want to risk losing the whole ship to a penetrating plunging shell that hits a magazine, so over the magazines the deck must be impervious to any gun at any range.

If someone puts 22in guns on a BB, the Mega would need to reinforce its deck. With maximum structural weight exceeding its empty weight by over a million tons, however, this is easy in one sense. It would, however, require dredging an East Coast harbor past 40ft, sending the ship to the West Coast for overhauls, putting a floating drydock in Provincetown Harbor, or removing some guns to maintain empty draft. None of these are prohibitive. You could also trade some guns for more deck armor in the original design, requiring, say, a 24in gun to threaten the MegaBB. It probably doesn't need 300x the Iowa's firepower to achieve its primary mission, after all.

And of course if Japan is forced to build 22in gun BB's then the Mega has forced them to waste precious resources. Unless they build a ship on Mega scale, those 22in BB's can be sunk by carriers - Carriers that would face far fewer Japanese carriers, while the U.S. carriers would be behind an impenetrable Flak wall put up by the MegaBB's. So maybe you leave the MegaBB's as they are and tie them to the carriers until the 22in BB's are sunk.

[TheMarcksPlan]

Re-upping this discussion. For ease of discussion and (hopefully but probably belatedly) to avoid acrimony and aggression, let me clarify/concede a few things at the outset:

• 1. The primary motivation here is intellectual curiosity about theoretical possibilities of ship size. This is for fun more than anything. Take it in that spirit.
• 2. The political conditions for the U.S. to have employed the resources for this ship would require a large political deviation from OTL. Several "What Ifs" involve similar deviations. More on that below.
• 3. The military conditions for building this kind of ship would require exceptional foresight - the typical AHF accusation of "hindsight" is not unreasonable. Nonetheless, perhaps an analyst with exceptional foresight could have seen the benefit of building this ship were doing so politically and industrially feasible.
• 4. Even were the political/military/industrial conditions for building this ship extant, the critical question of cost would remain. I have a guess on that figure ($2-3bn) but it's only that.

The Purpose/Benefits/Rationale of a Megaship

The fundamental rationale is, as stated in the OP, economies of scale. As the U.S. is the world's richest country, it alone would be capable of building the largest-feasible warship(/transporter). For any other country to match the combat power of a maximum-feasible warship, that country would have to expend scarcer resources with dis-economies of scale. IF the U.S. decided to devote 1% of GDP to naval construction in, say, 1933, the megaship would, I argue, yield more benefit than smaller ships of equal cost.

What's more, a megaship would be built with the explicit rationale of being multi-purpose. It could function simultaneously as (1) battleship, (2) aircraft carrier, and (3) strategic transport. In fact, the value of the ship would probably go (3), (2), (1). Its value as a transporter could alone justify its cost (had U.S. planners foreseen massive overseas deployments).

As further discussed below, once you've built a ship large enough to destroy extant enemy battle fleets in a surface engagement, the marginal cost of adding additional size/capability for roles (2) and (3) is quite small and the benefits enormous. Space for hangars (which can also act as cargo holds served by AC/cargo elevators) is, compared to "normal" carriers and cargo ships, extremely cheap. Special cargo infrastructure would be needed, however - more on that below.

Besides being efficiently multi-purpose, a Megaship could be extremely fast - 40 knots or higher. This renders it able to dictate terms of engagement and avoid risky situations. Practically-unlimited range opens up additional possibilities and relieves logistical burdens for forward operations.

So how big are we talking now? Big enough for the hull-girder and citadel to coincide.

The fundamental size-driver for an arguably-affordable megaship is:

Big enough for the armored citadel to be made of structural steel - thereby making up the hull girder - and of sufficient thickness to constitute effective armor. A ship's hull can be analyzed for strength purposes as if it is a giant girder - here I'm taking that concept literally (at least for the citadel, which constitutes the most-stressed part of the hull). Because structural steel has lower effectiveness than hardened armor, and because we want the mega-ship to be very well-armored, this thickness has to be very high. The point at which an armored box of sufficient (armor-equivalent) thickness weighs around as much as a typical hull girder implies a very large ship. In the background of this post is a set of iterative estimates that I won't get into just yet. Let's just play with a million tons of steel in the citadel/girder, as that's around where I landed.

One huge benefit is that structural steel is relatively cheap - $47 per long ton in 1940. https://fred.stlouisfed.org/series/M041 ... 00M287NNBR Thus a one-million-ton citadel/girder would cost $47mil for steel/armor (half the cost of BB Iowa). Just as fortifications can use concrete because cost is more important than weight, so could a megaship use less weight-efficient structural steel as citadel armor to economize on cost while making additional hull strength redundant. Turrets can remain face-hardened or (more likely) homogenous armor.

How much of a weight penalty, compared to equivalently-strong homogenous armor? Per Nathan Okun's research, WW2 "mild-medium" construction steel was 20% less effective than homogenous armor, "high-tensile" steel 15% less effective. There was an adverse scaling effect, however, so we're going to make our armor somewhat stronger than these simple ratios require. Let's use high-tensile steel for the citadel/girder; even if it's twice as expensive as the above-quoted structural steel that's "only" $94mil for a million-pound citadel.

What steel thickness do we require? As said in my last post, we'd want a mega-BB's deck armor to be invulnerable to feasible enemy guns at any range. What does that mean? Well the super-heavy U.S. 16in shell can penetrate 14.05in of homogenous deck armor at max range. We'd want to anticipate feasible growth in enemy guns, say up to 24in (with room to add more protection if needed - discussed below). As shell penetration increases roughly linearly with shell diameter, a 24in super-heavy shell could penetrate ~21.1in of homogenous armor. We'd need 24.8in of mild steel to resist that shell. To account for scale effects and to give some margin of error, let's say 30 inches of mild steel for the citadel deck.

For the side armor, let's say 36in for now, just to maintain side>deck. Using the above-cited formulas/figures, that gives an inner immunity range of 20,000 yards against ~23in shells. The megaship will be invulnerable against "normal" battleships to closer ranges but in all cases its tactic will be to fight from very long range and it will have the speed to dictate range (discussed below).

Benefits and limits of size efficiency

With minimum deck/side armor thickness set, we have a dynamic wherein the ship's volume/displacement increases cubically (up to a point) while its armor weight increases only quadratrically. The residual space/weight enhances the ship's damage survivability, its usefulness as a transporter and (to a lesser extent) as an aircraft carrier.

The point at which the limit appears is when draft becomes excessive. Unlike in the OP, I've accepted that this ship will be able to operate from only a few specially-modified ports. Using construction steel instead of naval armor makes it simply too heavy for 37ft draft even at light ship displacement.

For various reasons I've set maximum battle-draft at 110ft. This forecloses operation in a few areas - English Channel, southern North Sea, Sea of Java - but on the high seas and around the Philippines is fine. Under normal combat conditions, 30ft of this draft will consist of ballast.

From maximum draft we have a maximum practical hull thickness. As the citadel box encloses the entire freeboard around the turrets, I figure a maximum freeboard of 80ft. That implies 190ft hull depth.

To keep ratio [hull depth] : [length] to levels <20, maximum length would be around 3,800ft. Let's say 3,300 feet for now.

At this length, the ship has a speed-length ratio akin to WW1 battleships even at 40 knots. So I use a WW1 hull form:

Length:beam ratio of 6:1, beam=550ft.

Block coefficient of .665 so

Battle displacement = 3.85mil long tons.

Citadel/girder dimensions:

LOA: 2,000ft
Width: 350ft*
Height: 190ft*
Bulkheads: 350ft x 190

*To complete the hull girder box, the keel has 12in-thick steel. Likely to be distributed in layers over a triple bottom 20ft thick (containing fuel and ballast space).
**Only upper 90ft is 36in thick; lower is 12in (backstopping 100ft torpedo bulges, rendering magazines etc. unreachable).

Using 490lbs/ft2 for steel, arithmetic gives me 916,344 tons of citadel/girder steel.

For a very basic check of whether the citadel/girder gives sufficient strength, compare it to a large ship like Emma Maersk. Its empty weight is ~50,000 tons, deadweight is 156k tons. If the ship is ~3/4 hull girder by weight, that's a ~4:1 deadweight:structural ratio. The megaship's citadel/girder is only ~3x the remaining max displacement (3.85mil - 916k), not all of which is non-structural.

Citadel volume (excluding 20ft of void) is 1.19mil GRT - equivalent to nearly 15 RMS Queen Mary's. At 4 GRT per crew member for accommodations, holding a 100,000-man crew would required only 1/3 of the citadel space. As propulsion volume will be relatively small (more on that below), there's plenty of room for enormous ordnance stowage and machinery.

Beyond the main citadel box would be hangars,

What kind of armament?

As in the OP, a megaship would be designed, initially, to carry "only" 18in guns - albeit hundreds of them. This is because:

• The megaship would seek extreme long-range engagement (>45,000 yards) and the armor thickness required to stop a plunging 18in shell (>16in) is impractical except on another megaship. Larger shells are, therefore, overkill except against other megaships.
• As discussed upthread, I believe it was possible to design a higher ROF for 18in guns using the greater volumes enabled by the no-barbette (i.e. flush armored deck) design. I am less confident that is true for much bigger guns.
• Firing thousands of shells per minute over a given area would enable the megaship to use barrage strategy - any reasonably-sized opposing navy will cover at least 1% of a large target area. This will gaurantee dozens of plunging and penetrating hits per minute regardless of enemy maneuvering, which means even a large fleet is significantly weakened in the opening minutes of engagement, even without fine range acquisition.

As in the OP, the megaship's turrets have multiple rows of guns - though critically none of the guns are on top of each other.


There's room on the citadel for at least 1,000 18in guns; quite so many are not strictly necessary. The program could envision leaving space for them and procuring/emplacing only so many as dictated by foreign naval capabilities as completion neared. Space freed up could be used to enhance aircraft

As part of a megaship project, USN would also design a larger-caliber gun - 24in? - to counter a foreign megaship. Her turrets would be large enough to accommodate fewer of the larger guns. The bigger guns would be produced only in response to a foreign megaship. Of course the megaship would exceed Germany/Japan/UK's naval budget so is highly unlikely.

Secondary armament: Because this ship makes weight of secondaries basically irrelevant, and because topside space is at a relatively greater premium to weight, I'd expect the USN to develop a high-ROF 6in/8in DP gun for the megaship. USN began working on the 6in/47 in 1937, for example. Put a few hundred on board to deal with any cruisers/destroyers that might attempt to close during a fleet action and to add AA fire.

Anti-aircraft As the megaship has an ~8,000ft perimeter and 80ft of freeboard, several layers of sponsons can be hung off the hull containing 40mm, 75mm, or other AA weapons. With, say, three vertical rows of quad Bofors (extending down to 50ft above waterline) spaced 25ft apart horizontally, megaship could mount ~4,000 Bofors. At 100 rds/min and 1,500 rds/kill on average, those guns alone could shoot down ~250 planes per minute. In other words, only if the entire Kido Butai's air wing lined up for a perfectly-executed simultaneous attack would be expect significant planes to get through. And of course that assumes the primary guns acting as long-range AA and the secondaries do nothing.

As it's not really possible to inflict serious damage on the megaship with carrier-borne weapons, the ship's strategy should be to welcome any naval air attacks.

Speed and Propulsion

The megaship should be extremely fast - at least 40 knots.

First, let's look at the basics again.

A ship's friction resistance is proportional wetted area, coefficient of friction, and the square of speed.

Compared to BB Iowa's dimensions, I estimate 15.55x the wetted area (4x as long, 5x as wide, 3x as deep - I can say more about the calculation).

Coefficient of friction offers a surprising result (see pages 10-16): I get a 5% lower coefficient for megaship than BB Iowa based on the cardinal dimensions (again can reproduce arithemetic on request).

This is because, despite lower length:beam and higher block coefficient, the megaship has a much higher Reynolds number due to greater length and (at 40kn vs. 33) higher speed. Again, economies of scale.

.95 * 15.55 = 15.07 ----> at equal speed and propulsive efficiency much more efficient given >60x the displacement.

But that's only ~half the story in Iowa's case. With a high speed-length ratio of 1.12, probably nearly half of Iowa's resistance is wavemaking.

--------------------------------------
Aside:
To roughly quantify this effect, I looked at speed/HP/RPM data for Iowa-class on various trials. Data here:


If wavemaking drag were insignificant (it is at very low speed-length ratios), we'd see ship resistance rise with the square of speed. We can infer roughly the ship resistance delta between two speeds by taking the HP delta (between speeds) and taking the (2/3) power of HP (HP cubic with RPM, ship resistance and propeller thrust roughly quadratic with RPM).

Between ~20kn and ~30kn, Iowa's require >30% more speed than simple quadratic escalation of resistance suggests. If wave drag is ~20% of drag at 20kn, that's consistent with nearly 50% at >30kn.

------------------------------------------

As the megaship is 3.83x as long as Iowa, its wavemaking resistance at 40kn is proportionately similar to Iowa's when traveling at 24.8kn - thus a fuller hullform is appropriate.

Combining 25% vs. 45% wavemaking fraction with the above friction and speed parameters - and using the same prop RPM - I get 3.2mil HP to drive the megaship at 40kn:



RPM matters a lot here: It's often said that speed and HP are related cubically: 8x the HP for twice the speed. That's true when looking a single boat: unless you can make propellers magically appear, the only way to go faster is to increase RPM, which is cubic with HP (speed * torque).

With the megaship at 225 RPM, it needs 16x the HP and propeller area equivalent of 64 Iowa propellers.

As a fraction of underwater cross section (beam * draft), however, the megaship would be using only slightly less area (25.6%) than Iowa (26.5%).

But not all underwater area can house propellers: stick the edge near the surface and low pressure will cause excessive cavitation. It's probably only the area >10ft below water that matters for big propellers (only 25ft of depth for Iowa at 35ft draft). By that metric, Iowa uses 36% of available area.

If megaship's props also covered 36% of the area 10-110ft below its waterline, its RPM at 40kn could be reduced to 190, which decreases its HP required by 10.7% to 2.87mil.

Finally, cavitation is lower for the deeper propellers - ambient water pressure is 4.6x higher at 90ft than at 20ft. Crediting Iowa with 33kn performance is probably not accurate due to cavitation but that wouldn't be a problem for megaship.

--------------------------------------------------------------

Well that's enough for now. Some quick points:

• Electric propulsion. Diesel/Turbine.
• Propulsion survivability. More propellers are harder to take out. Additionally, electric power would mean HP can go to any of the propellers. As the deep propellers are nowhere near their cavitation limit, they can be spun up to 2x normal RPM (4x the thrust) in the unlikely event that over half of the propellers are lost. So with 87.5% of propellers knocked out, the remaining 12.5% at 4x normal thrust (8x normal per-shaft HP) can provide half the normal total thrust, which is good for >28kn. Torpedoes can't chase down a 40kn ship from the rear anyway. In short it's virtually impossible to immobilize the ship without penetrating the citadel to kill the generators.
• Carrier decks extend over the waterline. 100ft-wide decks on each side easily doable (Nimitz has far higher ratio of max beam to WLbeam). 2,000ft+ runways on each side, 800ft runway forward, 600ft rear. Triple takeoffs/landings possible, as are simultaneous/continuous recovery/launch. Hangar volume potentially equal to >50 Essex CV's (would take 18% of hull volume). Beneath wing decks could a "deck loader" for spotting next launch, with 20:1 grade ramp using remaining ship length, removing plane-spotting burden from flight decks.
• Deadweight tonnage of 2mil for transport operations; 2.5mil if turrets/guns removed. Cargo space equivalent to 300 Liberty Ships, weight 200-250. Capable of moving >10 divisions, with all vehicles on wheels, at a time.
• Given greater speed and no convoy/escorts needed, equivalent to >1,000 Liberty Ships on North Atlantic run. As Liberty Ships cost $2mil, megaship is worth >$2bn as a transporter alone (setting aside Liberty Ship escort costs and megaship's infrastructure requirements for now).

[Terry Duncan]

This thing is going to exceede even the US budget, indeed it will likely use all of it for many years to come. Even then it can only be in one place at a time and has no depots it can rely on. People didnt build such freaks for very good reason, the Tillmans are about as far as anyone got other than the H-44 and super-Yamato's and all were rated as undesirable by the navies concerned or simply impractical to build and support.

[T. A. Gardner]

Of course it has to be considered! That's the entire reason that a MegaCV might offer worthwhile benefits! It has a longer runway for larger planes [and hangar space for them]!
Re the exact takeoff run required for a loaded A-26 or whatever - I don't know. Anyone have those figures?

I might have mentioned this earlier in this thread, but I don't want to wade through the whole thing to find out.

Another consideration for carriers is air wing size. Yes, you can have too many aircraft aboard a carrier, as well as too few. The USN found the optimal size was to have 3 or 4 strikes worth of aircraft aboard ship and size the carrier to that. The strike size is the number of planes you can launch before you have to clear the deck to allow the last strike to land. That cycle time dictates how many aircraft you can have aboard that are usable.

When the USN first looked at building the Midway class, they were concerned that the ship's air wing was too large at about 130 planes. As the war progressed and plane size grew it was determined that future use would bring the number of planes down to where they could be efficiently cycled. That today dictates the size of large carriers, just like it did then.

Large twin engine aircraft were tried aboard US carriers late in WW 2.



That's a B-25... Well PBJ-1H aboard the USS Shangri La in late 1944 doing landing, free take off, and catapult launches. As you can see, the size of the plane on an Essex class nearly overwhelms the flight deck. It would be difficult to carry many aboard and their deck space for launches and landings would eat up a lot of room that could be used with smaller planes.

Planes in the 50's and 60's for nuclear strike like the AJ Savage or the A3D Skywarrior were accepted only on that basis and in very limited numbers. The latter continued to be used into the 80's as an ELINT plane with carriers having one or two aboard.

So, it's unlikely the USN would willingly want to build a huge budget busting carrier just so they could launch medium bombers. There is no real practical value in that. Better to get two smaller carriers with usable air wings that are flexible and can carry out a range of missions. The other value in that is you now have two targets not one. If the mega CV is damaged and unable to launch you have no air power. If one of two of your smaller carriers is damaged you still have 50%+ of your air power good to go.

[TheMarcksPlan]

This thing is going to exceede even the US budget

Depends on the budget and megaship's cost. 1940 navy budget was $1.14bn, about 1% of GDP.

As stated, the ATL requires greater US commitment to its navy in the 1930's; that implies a bigger budget. Something like 1940's budget.

If the megaship costs $2.5bn, that's $500mn per year across a 5-year program. Less than half of the 1940 Navy budget.

At least as important is the Merchant Marine budget. MARCOM ships counted 6,000 during the war - that's probably on the order $15bn spent. The megaship would provide transport lift more efficiently than MARCOM ships (discussed above) and is therefore economically justified even if lacked guns and aircraft.

the Tillmans are about as far as anyone got other than the H-44 and super-Yamato's and all were rated as undesirable by the navies concerned or simply impractical to build and support.

I don't see these as analogous. They're just slightly bigger traditional battleships that can still be readily sunk by carrier aircraft. Megaship is 50x larger than Super Yamato, 35x larger than H-44. It's like comparing Yamato to a DDE.

The specific judgment on H-44, IIRC, was (aside from infeasibility of Germany building any battleships) that it was vulnerable to the Grand Slam bombs that sunk Tirpitz. As Grand Slam bombs can penetrate 16ft of concrete (equivalent to ~16in of homogenous armor), the megaship's 30in decks are invulnerable.