This would be harder to do than the KGVs but the 6 armoured aircraft carriers laid down 1937-39 were also seriously delayed. All were planned to be built in exactly 3 years. However, only Illustrious came close to meeting her scheduled completion date. This list has their actual completion dates followed by their planned completion dates.
25/05/1940 - 01/04/1940 - Illustrious - 1 month late
15/05/1941 - 01/05/1940 - Victorious - 12 months late
10/10/1941 - 01/11/1940 - Indomitable - 11 months late
24/11/1940 - 01/06/1940 - Formidable - 5 months late
28/08/1944 - 01/02/1942 - Implacable - 30 months late
03/05/1944 - 01/11/1942 - Indefatigable - 18 months late
Had Victorious and Formidable (along with the projected expansion of the FAA) been completed on time the Mediterranean Fleet could have attacked Taranto with 3 aircraft carriers instead of one; had 3 times the fighter cover when it met Fliegerkorps X off Malta in January 1941, attacked the Vittorio Vento (if it had survived the TTL Taranto raid undamaged) with 3 times as many aircraft; and had 3 times the air cover off Crete in May 1941.
Indomitable would have taken the place of Victorious in the Bismarck chase. As Indomitable had been completed 6 months earlier than Victorious ITTL she might have had a full-strength air group which was also fully trained.
As I have brought forward the ordering of the long-lead items for the King George V and Lion class battleships forward by a year in Post 89 I'm going to perform a similar trick for the Illustrious class carriers.
That is there is a quicker reaction to German rearmament by the British Government. IOTL full-scale rearmament did not begin until 1936 but hindsight tells us that they should have started in 1934. ITTL I'm splitting the difference with rearmament beginning in 1935.
ITTL the First Report of the Defence Requirements Committee recommended that the aircraft carrier force be modernised and brought up to the 135,000 tons permitted by the Washington Naval Treaty ASAP. Later in 1934 the Government announced plans to build 5 aircraft carriers. 2 were to be laid down in 1936, 2 in 1937 and one in 1938. Each ship would take exactly 3 years to build. By 31st March 1941 (the end of the 1940-41 financial year) there would be the 5 new carriers and Ark Royal. All the older aircraft carriers would have been scrapped or converted to depot ships. The aircraft and aircrew needed for the aircraft carriers were incorporated into the TTL version of the RAF's Expansion Scheme A.
Thus Illustrious and Victorious were ordered in the 1935-36 Estimates instead of the next year's estimates. They were laid down in April and May 1936 respectively instead of a year later. If completed in the same length of time as OTL we would still get Illustrious in May 1939 instead of May 1940 and Victorious in May 1940 instead of one year later. However, ITTL I think Victorious would have been completed sooner than that.
Formidable and Indomitable were ordered in the 1936-37 Estimates instead of 1937-38. However, the long-lead items were ordered in 1935-36. Although the original plan had been to lay them down in 1937 it was decided to bring it forward a year following the Abyssinian Crisis. Therefore Formidable was laid down in June 1936 instead of June 1937 and Indomitable was laid down in November 1936 instead of November 1937. All other things being equal Formidable would have been completed in November 1939 and Indomitable in October 1940 instead of October 1941. However, IMHO ordering the long lead items for these ships a year before the hulls would advance the completion dates by 6 months for Formidable and a year for Indomitable.
The result of all the above was that Illustrious, Victorious and Formidable were completed in the middle of 1939 and Indomitable was completed in October 1939. The abolition of the aircraft carrier tonnage quotas under the Second London Naval Treaty allowed the Royal Navy to retain Argus, Courageous, Eagle, Furious and Hermes which under the original plan had to be scrapped to remain within the tonnage quota. (Under original plan Glorious would have been replaced by the ship ordered in the 1937-38 Estimates).
Meanwhile as IOTL in October the Admiralty changes its plans for aircraft carriers from a force of 6 ships (5 IOTL) to 15 ships (14 ITOL) which the impending abolition of the Washington Naval Treaty tonnage quotas allowed. As a result 2 aircraft carriers were ordered in the 1937-38 estimates instead of the single ship that was previously planned. Their long-lead items were ordered in 1936-37.
These ships were Implacable, which IOTL was ordered in 1938-39 and laid down in February 1939 and Indefatigable ordered in 1938-39 and laid down in November 1939. ITTL Implacable was laid down in February 1938 for completion in the first quarter of 1941 instead of October 1944. ITTL Indefatigable was laid down in November 1937 for completion in November 1940 instead of May 1944.
IOTL the plan in late 1935 was to order 2 aircraft carriers a year 1936-37 to 1940-41 so that when they were completed there would be a force of 14 ships made up of Ark Royal, 10 armoured carriers and the 3 Follies. However, ITTL only one ship (Implacable) was ordered in 1938-39 and one ship (Indefatigable) was ordered in 1939-40. AFAIK only one ship would have been ordered in 1940-41 if war had not broken out. Sources differ on which programme Eagle and Ark Royal were ordered under, but they weren't actually laid down until 1942 and 1943 respectively because the yards were full of ASW escorts and damaged ships.
ITTL the original plan in late 1935 was to order aircraft carriers at the rate of 2 per year until there was a force of 15 ships made up of Ark Royal and 14 armoured carriers. The plan was stuck to ITTL. 2 ships ordered in 1938-39 and laid down by 31st March 1939. 2 ships were ordered in 1939-40 and laid down before 31st March 1940. However, in common with the earlier ships the long-lead items were ordered in the previous year's estimates. Therefore it might be possible to have the 2 ships ordered in 1938-39 completed in the financial year ending 31st March 1942 and the 2 ships ordered in 1939-40 completed by 31st March 1943.
Thus the situation in September 1939 ITTL would be:
- Illustrious, Victorious and Formidable working up after being completed in the summer of 1939
- Indomitable nearing completion
- Implacable and Indefatigable under construction and due for completion by 31st March 1941
- 2 armoured carriers under construction and due for completion by 31st March 1942
- 2 armoured carriers on order and due for completion by 31st March 1943
That is a total of 10 aircraft carriers consisting of 3 working up, one nearing completion, 4 under construction and 2 on order.