This raises a number of interesting questions.
Firstly design & development of carriers and carrier aircraft virtually stopped in May 1940 with the German invasion of France and the Low Countries as there were much higher priorities. It doesn't pick up again until the latter part of 1941 following the lessons of the first half of 1941 in the Med. The first product of that renewed effort is the Colossus / Majestic design and then the Audacious class during 1942.
In terms of aircraft design, aircraft max weight limits had been around 10,500lb until 1940 when they began to be relaxed to 12,500lb for the likes of the Firefly & Firebrand. But everything came out heavy. The Barracuda designed initially around 10,500lb came out at 14,250lb in production form in 1942. The same thing happened in the US. The Curtiss SB2C Helldiver design began at 10,200lb in Nov 1940 and in initial production form in Sept 1942 was at 16,600lb. The TBF-1 Avenger started at a max weight of 15,905lb in early 1942.
A technical committee reported in late 1942 about the future direction of naval aircraft development and realised that they would be even heavier if future and also larger dimensionally. Any ships built from then on would have a significant postwar life and the weight increases were likely to continue. Designs exceeding the 20,000lb limit begin to be requested in 1943. Fairey Spearfish (19,000lb limit came out at 22,000lb when it flew in 1945) & Short Sturgeon (24,000lb limit).
In 1942 the Admiralty realised that it will have to depend on the US for its aircraft for the forseeable future so will have to ensure its carriers can take them physically. The first recognition of this is that hangar heights are increased to 17.5ft to match the standard US hangar height. This can be seen as the designs of the 1942 carriers evolve during the year. 17.5ft allows the carriage of the F4U Corsair without clipping 8" from each wingtip. But looking further ahead the USN had in 1941 begun to develop a successor for the Avenger in the shape of the BTD Destroyer which was planned around 19,000lb.
So everything in 1942 points to a new higher weight limit above 20,000lb being needed but I don't believe that it would have been so clear to anyone in 1941.
But the changes to aircraft design also have an impact on the ships and the yards that were to build them.
Increasing the hangar height in the Audacious class design didn't happen until Nov 1942 and that needed an increase in beam to accomodate the extra topweight. In turn that meant the the original Eagle had to be moved from Swan Hunter to VA(Tyne) as the SH slip was no longer wide enough to build it. The design was also modified for 30,000lb aircraft.
If Centaurs were to be built in place of Colossus/Majestic then the issue of a yard's ability to accomodate them needs to be considered. Alexander Stephens & Sons on the Clyde built Ocean. They couldn't have built a Centaur. They didn't have a slip long enough (Ocean was the second longest ship they ever built. The longest was a tanker in 1962 after substantial investment in the yard post-war).
Then the question of build time. In late 1941 an Admiralty study estimated the build time for a fleet carrier at 46 months and a cruiser at 28 months. Early Colossus studies indicated a build time of 24-42 months depending on spec. The first 5, the wartime completions, averaged 30 months. If you build the bigger Centaurs to their better spec better suited to the post-war environment, the build time will inevitably increase. And as Centaur used a half set of Audacious machinery, instead of the already designed half set of cruiser machinery in a Colossus, there will inevitably be delays in laying them down. So at least the early completion dates will move to the right. But by how much? 6 months? 12 months?
And at Harland & Wolff Belfast if a Centaur version of Glory takes longer to build, then a Centaur version of Powerful which was laid down on the same slip the same day as Glory was launched, also gets delayed. H&W was incredibly busy with slips lying unoccupied for minimal periods of time in WW2.
If the Colossus were laid down as Centaurs in 1942 with longer build times, then the future of the historical Centaurs ordered in July 1943 becomes even more problematic. They were seen as post-war ships by the politicians and as necessary to operate the new larger post-war generation of aircraft by the professionals. So would they even be ordered in the first place? And if ordered would there even be the historical compromise of agreeing to lay down 4 and defer 4. Wartime money that can be better spent elsewhere. The professionals have even less reason to insist on their progression. And if not started construction in the first place no need to spend money on work to allow the slips to be cleared by taking them to the launch stage. An easy cull in Oct-Dec 1945.
And with the Centaurised Colossus in the yards for longer what is the labour effect on both them and other programmes in the yards? The Transport Ferry/LST(3) programme affected the major carrier yards like VA(T) causing delays to the original Eagle. But H&W, Hawthorn Leslie, Swan Hunter, Stephen Fairfield, and VA(Barrow) were all involved in building both types and the LST(3) was a high priority in 1944/45.
Over at Cammell Laird work on Ark Royal was held up in 1944 by the need to get Venerable completed and the commitment of the yard to submarine and destroyer programmes. If a Centaurised Venerable takes longer what are the knock on effects?
Moving to the end of the war, with delays to laying Centaurised Colossus ships down and longer build times the result is fewer wartime completions and more ships of the class further away from completion. Without the need for for the historic Centaurs to be worked on to clear the slips money is saved but that doesn't mean that it would automatically flow to completing the Theseus & Triumph (Warrior had been promised to Canada who were keen to get into the carrier game but were happy to see Magnificent, which was not that far from completion historically, laid up). Stopping work on Majestic, Leviathan, Powerful & Terrible historically saved about £3.2m. That sum would be greater if they were building as Centaurs.
So come 1948 the very best that can be hoped for are 5 Centaurised Colossus in service (with 1 each gone to Canada, France & the Netherlands) as historical, with the 6 Centaurised Majestics laid up as historical and probably in a less advanced state of completion and none of the historical Centaurs. Then the question is will Australia & Canada want to spend more money to get another carrier, albeit a larger one?
Another issue is that while we have talked about the greater deck strength to take the new generation of aircraft, we have not discussed the ability to launch and recover them. The BH.III hydraulic catapult was standard in WW2 and steadily upgraded to launch 16,000lb at 66 knots using the trolley or 20,000lb at 56 knots tail down (upgraded to 20,000lb at 66 knots tail down in 1949). The improved BH.5 began in prototype form in 1948 and entered service on Centaur in 1954 (prototype 20,000lb at 56 knots; production 30,000lb at 75 knots). Wartime arrester systems were upgraded for heavier aircraft between 1945 and 1950. But new systems as fitted historically to Eagle & the Centaurs didn't begin development until 1946.
So if there are any Centaurised Colosus around in 1948 they still need refitted to bring them up to the standard of the historical Centaurs in 1954. Do you then move then delay those refits to take advantage of steam catapults?
So the question then becomes one of whether delaying service entry of these ships even further is worth the post-war benefits of larger ships that still need considerable modernisation?
