It also depends on how plausible a POD is that can achieve a "no-WWII" situation.
I think the key would be, prevent Germany from going authoritarian, militaristic and revanchist. If we can imagine the Weimar system somehow muddling through the crisis of the early Depression years without being taken over by the factions that led the Third Reich OTL, then Europe will remain at peace; Mussolini alone won't dare rock the boat too much in a Europe with no one to counterbalance the power of the Entente leading powers, France and Britain.
And perhaps this alone is almost enough to keep Japan from daring to get too adventurous in China, thus heading off the Pacific theater of the OTL war. Not quite, I'd think the European powers would have to assert themselves, presumably via the League of Nations, to deter Japan's militarists. Perhaps the long-standing alliance of Japan with Great Britain continues, and the intervention takes the form of Britain leading the League to make economic concessions that win over certain factions in Japan and forestall the takeover by militaristic elements.
In such a world there would indeed still be one obvious threat that the other powers would arm against--the Soviet Union. What I have here might essentially be called a "Liberalwank." In a Liberalwank world, I don't believe Stalin's regime would have necessarily been a lot different from OTL until 1939; at that point the change is, no change--there is no alliance with the Nazis to partition Poland and Eastern Europe generally, then no attack by Germany, hence no Great Patriotic War.
Would Stalin start a war himself? I think not, because he was of two minds, or one paranoid and schizophrenic mind, about using the Red Army to spread revolution from one country to the others. I believe that he did believe it was his duty and fate to do that, and accordingly his Five Year Plans leaned very heavily on military development. He would indeed have some serious intent to use these forces someday in the near future. The paranoia and schizophrenia came in when he considered that for a Soviet army to have the force and competence to prevail against the combined power of the capitalist nations, he'd need to raise up generals who would also be competent to overthrow himself. Accordingly, OTL and here, he'd assemble such forces, only to decapitate them by purging them.
He'd never get around to actually launching the war.
Eventually he'd die, of course, and I can imagine that without the transformations the Soviet system and his own cult of personality underwent in the Great Patriotic War, he might be killed off earlier. This might lead to the collapse of the USSR, but I think more likely something analogous to what happened OTL--there is a power struggle and a game of musical chairs in the Kremlin but what emerges is a coalition of survivors of the Stalin years determined never again to let one of their number take supreme power in that way. The gray apparatchik regime this implies would essentially continue Stalin's military policies--prepare for war at a pessimistic fever pitch, but enjoy peace as long as they gloomily hope they can.
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Now that I've outlined how a non-WWII world might exist, I think maybe it could last without any great wars indefinitely. The main reason it wouldn't would be if our OTL experience with the big war, including of course the nuclear balance of terror that emerged postwar, has a big bearing on why other conflicts than the leading ones of WWII have not blown up into big wars themselves. We've had no great wars since WWII but a whole lot of violence has happened anyway; without the lessons of that war and the postwar bipolar East/West Cold War prevented from spinning into an open hot war by the nuclear balance of terror, wouldn't there be major conflicts in places like China eventually leading to another Great War anyway?
Maybe not, if the POD miracles I've described are achieved by Britain and France taking the League of Nations seriously and developing League power to an effective "stick" counterbalanced by serious diplomatic "carrots" to defuse these conflicts and mediate satisfactory peace. Obviously the crises of colonialism in my view anyway pose a major challenge; the anticolonial movements would I think still gain momentum and to prevent this great crisis from breaking down into civil war within the British and French empires (and smaller powers like the Netherlands also would have their crises that might trigger ruptures in the big ones) the diplomacy of the Entente powers would have to be visionary and magnanimous.
If this desirable outcome could be attained, would it mean a general and universal disarmament that would make the whole question of the composition of nonexistent naval fleets moot? Probably not. If sentiment and economic stringency in the League and other Western powers urge disarmament, I'm sure that Stalin would agree--verbally and in principle. The trouble is, there's no way he and his successors would agree to allow meaningfully comprehensive inspections of the reaches of the USSR to verify Soviet compliance, no matter how fair and generously reciprocal the Western powers are in allowing Soviet inspectors the same freedom in the West. There would be enough skepticism of Soviet sincerity in the West to prevent such sweeping proposals from being made seriously, so everyone would tend to remain armed.
But I do think there would be a gradual build-down, or rather, the sizes of military forces, naval ones in particular, would be in fact capped. Serious downsizing would require trust in treaties and universal compliance, but simply assuming that the forces deemed adequate in past generations will continue to be adequate in the future would set the sizes of forces.
So--for aircraft carriers to take over as the capital ships, other types of capital ships, ie battleships, would have to be scrapped. I suspect this would happen very slowly and only to a limited extent.
The positive value of carriers was indeed apparent; the idea that fleets might do without battlewagons completely however would not have been demonstrated; indeed battleships did have their uses in OTL WWII and have been used or considered for use a few times since, as heavy artillery platforms.
The navies might gradually replace many or most of their battleships with carriers, but they would balk at eliminating the last handful of battleships. With naval construction budgets limited and fleet sizes capped at traditional levels, the development of AC tactics and strategy in war games would be slowed. Not stopped, but much delayed.
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