Ordered as the fourth unit of the "Illustrious" Class, Indomitable had her design revised so that she could operate 45 aircraft instead of 33. The extra stowage could be provided only by adding an extra hangar deck; it was found that by reducing the thickness of the hangar walls from 41" to 11" it was possible to raise the 1500-ton armoured flight deck by 14 feet without loss of stability.
There was little external difference between Indomitable and Illustrious apart from the former’s increased freeboard.
Had it not been for her grounding in Jamaica while working up in November 1941 Indomitable might well have been sunk the following month, as she was originally intended to join the battleship Prince of Wales and the battlecruiser Repulse at Singapore - and both those ships were sunk in December 1941.
Indomitable was another who had her flight-deck armour pierced by an 1100lb bomb, in the Mediterranean in August 1942; that and another hit aft where there was no armour put her out of action until February 1943. The following June she was torpedoed off Sicily, and was out of action until April 1944. She then joined the Eastern Fleet and in January 1945 the British Pacific Fleet. In April she was hit by a Kamikaze which simply slid up the armoured flight deck and over the side.
In reserve from 1947 to 1950, Indomitable then spent 3 years with the Home Fleet before paying off for the last time.

* = Extended to 745’ in 1943