The last two member of the class, Illustrious and Inflexible, had been laid down 6 months after the first pair. The (whatever) Treaty halted construction on all four vessels and the US and Japanese construction programs as well. Each country was allowed under the Treaty to complete two of their uncompleted ships as gun armed ships while two more could be converted to ships to operate wheeled aircraft. Indefatigable and Indomitable became the battlecruiser (later rated as fast battleships) pair, while the Illustrious and Inflexible became the aircraft carrying pair.
The ships were huge with a double storey hangar capable of fitting over 90 aircraft internally. Two large lifts at each end of the hangar decks transported aircraft from both decks to the flight deck. Not having the same topweight restrictions as the smaller Courageous class, the hangars were carried right forward as far as the enclosed bow would allow. While the US and Japan went for carrying the largest guns allowed by the Treaty, 8 inch, the Illustrious class carried a much more modest armament of 4.7" and 2 pounder AA guns.
I will add the top view once I finish it. Then the later 40-42 update drawing.