As part of Strategic Defence and Security Review, and in addition to the axing of the Harrier force and "Illustrious"s sister ship , it was announced that a short study would be carried out to determine whether "Illustrious" or "Ocean" was the most viable helicopter platform. The decision was subsequently made to retain "Ocean" for the longer term. In May 2011 "Illustrious" was made operational after a £40 million refit, and she was handed back to the fleet after sea trials in late July 2011