300,000 tons or more https://en.m.wikipedia.org/wiki/Project_Habakkuk
Midway class, as designed, standard displacement was 45,000 tons. Does this include weight of the aircraft? By the 1990s the Midway class were 69,000 tons standard
Whittle has a better trajectory for his jet development in the 30s, and has a jet flying in 1936 or so and a jet fighter in service by 1940.
Carriers get bigger to deal with the bigger, faster and heavier aircraft and the Indomitable class top out at 70kT In 1944.
Problem with this is that there isn't a reason for that sort of size. Shinano was that heavy because of her original design (lots of armored bulkheads to soak up tonnage). The USN figured out that it was damned near impossible to operate more than 100 aircraft from a single deck (Midway could handle around 130 late WW II aircraft, but it was like a monkey F$$$ing a football).
CalBear is quite correct, you dont need a 70kt carrier in WW2.
There's an optimal number of planes you can operate from a single carrier, depending on circumstances its around 80 planes. Having a few more is useful, but certainly there is no need to go over a hundred.
So the Midway or Audacious class are the optimal ships.
One idea I had was inspired by the "maximum Battleship" studies commissioned by Senator Tillman around the time of WWI. Maybe with the signing of the WNT, a similar "Maximum Carrier" study is initiated in a similar format to explore how big a carrier can be built (and how big can carrier aircraft get). Such studies could influence CV designs the way the Tillman BBs influenced US BB design.
Well, the thing about jets is that they are so much more effective that you simply do not need huge numbers. Same goes for later piston engine designs (the A-1 was roughly four times as capable as the aircraft it replaced, it was also fully capable of replacing two different aircraft (dive bombers and torpedo bombers). The F2H Banshee had 3,000 pound bombload while also carrying four 20mm cannon, with more range than the Corsair (nearly double) or the Hellcat (around 50% greater), something that sort of brings the "thirsy jet" concept into question (even the FH Phantom, which was designed in 1943, had nearly identical range to the F4U). Both of these aircraft operated quite happily from the Essex short hulls at 27,000 tons. The Midway class was meant to allow much larger air wings (as noted, this capability proved to be mainly a paper improvement), while also improving survivability and on station time. Both the Essex and Midway classes were able to operate the, for the era, enormous A3 Skywarrior without serious modifications (angled decks were more a matter of operational tempo and higher landing speeds than anything else), although the size of aircraft like the A3 (which was almost 2.5x the length of the F4U) pushed into the "supercarrier" era. As noted, even the Forrestal/Kitty Hawk/JFK supercarriers, which were able to operate everything up to and including the F-14, E-2C, and F4 barely meet the 70k ton cut-off at standard load. Add nuclear reactors, with the extra shielding and weight of the kettles, and you now can reach up to the 90k+ ton level (although it needs to noted that the de Gaulle manages quite nicely at 45k tons and the RN's new QE class just touches 70k with conventional propulsion).Go with @highwayhoss , carrier design studies happen on paper.
Then go with @Riain and have jets happen earlier, and be seen as THE answer.
For the Pacific War, you need range, which means huge amounts of fuel for those early fighters, possibly multiple engines (4 engine fighter, anyone?). So these 'fighters' will be big and thirstly.
Even with cats and traps, you may need a longer take-off, and so a bigger ship. More space used for runway may mean less deck-park available - or an even bigger flat-top to hold the planes warming up.
Many of the planes on-board this ship will be piston, still, so you need AvGas, JetFuel (given how thirsty the jets are, this ship may be half tanker), and bunkerfuel for the ship.
You might well need two-man operation of the jets, and refueling tankers....
So. You want 100 war aircraft, including, say, 35 jets. Which require tankers (converted medium bombers?), massive fuel supply. If you're using medium bombers as tankers, why not throw in some more as actual medium bombers....
Yeah, if such a design is being worked on in a back-office somewhere, and Pearl Harbor happens, .... I can see it rolled out, and ready by the end of the war. Barely.
It could be darn near SuperCarrier size.
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Edit. New thought. Forget the early carrier design. Just have jets arrive earlier, and have a huge buzz. Some admiral, wanting to keep short-legged jets off HIS ships, orders a reductio ad absurdum study of what might be required, deliberately coming up with such a massive ship that no one in their right mind would build one.
However, Kelly Johnson comes up with a jet that's (barely) feasible, the jetmania is in full swing, and .... Hey, we've got a plan here, it's the only one available. Let's build it!!! (Let's also spend a couple of years designing a more optimized ship for post-war, but we need SOMETHING NOW.)
(Hey, it's saner than Habakkuk or the Alaskas....)
The G3 or N3 were not Big enough, but how about if the N3 start as a hybrid battleship carrier design? Not far from it to start. Then in 1930's a relatively short aft deck is lengthened by adding an extra section amidships to increase speed (and weight),but sadly, engaging the Bismarck it is damaged in the front turrets and rebuilt as a full carrier. Making a flight deck above the armored deck adds more weight and voila, you have a super carrier - without any need for such a design.Lets say the G3 Battlecruisers were begun and due to the Washington conference being delayed by at least a year two were available for carrier conversions ending up much like the Japanese Shinano.