Re the threat of high-level superbombs from superbombers...
Main response, already stated, is that nobody but U.S. (maybe UK) can build enough superbombers to pose a credible threat to 36in of mild steel.
I should emphasize more clearly that the underlying physics favors the megaship, however. Per the already-quoted studies
, armor/steel penetration escalates linearly with diameter for a given shell/bomb form and striking velocity. So if you want to double armor penetration, your superbomber and shell/bomb have to be ~8x larger.
By contrast, a ship of sufficient size/firepower need protect only its vitals from unlikely superbomb hits, an area that remains basically constant. If we need to increase armor thickness linearly over a given area, the compensatory non-citadel delta to displacement and attendant propulsion delta are insignificant, given extremely favorable displacement/HP ratios for a megaship.
To put hard numbers on it: To protect against a B-36's max payload (86k lbs) in a single air-dropped shell/bomb would require ~51in of high-tensile construction steel. Over the same 2000x350ft citadel under discussion, that requires 191k tons more than 36in deck armor or 5% greater displacement, which would require ~3% higher HP for a given speed.
...that doesn't answer the question whether its feasible to build a megaship, but it does answer the question whether, within the megaship domain, escalating (non-nuclear) airpower reactions are feasible.
But the heavy bomber's threat to megaship is only half the question; megaship's threat to heavy bombers is at least symmetrical.
A megaship with 1,000 high-elevation 18in guns at 5/min RoF - feel free to quibble whether that's possible on the particular megaship I've sketched but it's feasible for a massive ship - puts up the AA weight of ~50,000 88mm flak guns. For comparison, the heaviest anti-HB flak concentration I can think of was around Leuna with ~1,700 heavy AA guns. Germany built 21,000 88mm guns during the entire war.
Per Westerman's Flak
, the German 88mm Flak 41 shot down a heavy bomber for every 5k rounds fired. With a megaship firing 5k 18in rounds/min and each shell worth ~142 88mm shells, that's 35 18in shells/bomber or >140 HB's/min.
...but that's based on German fire control practices and no VT fuses. With Allied fire control and VT fuses, 10 shells/HB is a conservative estimate (again per Westerman's Flak
, a late-war copy of Allied gun-laying radar tech - "Kulmbach" - reduced kills to 300 rds/kill or by a factor of >16).
Even with a probably-conservative 10 18in shells/HB, the megaship could kill 500 HB's per minute. That makes feasible destroying a 1,500-bomber force during its ~3min run at the megaship (and 3min assumes no evasive maneuvers by the megaship that force reassembly and go-arounds under megaship fire). Unless we're talking basically Kamikaze Japanese pilots of that massive bomber fleet (an economically implausible projection), the suicidal odds are going to cause skyrocketing "creepback"
and ineffective attacks against the megaship.
For another AA scale comparison, consider an Iowa/SoDak/Juneau-class ship firing 12 5in/38's at 15 rds/min. The megaship main battery's weight of fire is alone 1,320x as great (leaving aside secondary/tertiary guns for now). Attacks against any of those ships were guaranteed to lose at least a few planes OTL. It's likely the megaship could shoot down thousands of closer-flying carrier AC or other non-HB aircraft, were it possible to assemble so many AC for an attack.
The requirement to be functionally invulnerable to air attack is why my fun little sketch places DP main batteries at its center. It costs a lot to make a giant turret rotate at speeds sufficient for medium/long range AA fire, however. I estimate that the 15-20k ton rotating main battery turrets would each require ~30k HP to move adequately. That's feasible on the megaship because - unlike normal BB's, the rotating machinery isn't confined to a barbette and to the "electric deck
" below the gunhouse. As the armored deck is flush with topside, turret-rotating machinery fits easily outside the rotating structure rather than within.
As we'll need additional HP to ram quickly projectiles at the ~45-degree loading angle, and to hoist ~10,000t/min of shells and powder, I budget 1mil HP for total auxiliary machinery power. That raises the megaship's total to 4mil HP, still <20x an Iowa for 400x the surface firepower and >1,000x the AA punch.
And, btw, with electric drive the auxiliary generating capacity - functionally indistinguishable from main generator plant - can feed the props (which are well short of their cavitation limits). So a megaship making an operational dash to attain favorable tactical position (i.e. when it doesn't need to rotate/load the main battery) can do 43-44kn.