Some important modifications were made to her flight deck arrangements, including the installation of a new aft lift and modification of the catapult for use by American-built aircraft. Her light antiaircraft armament was also augmented during the refit. Captain Lord Louis Mountbatten relieved her acting captain on 12 August, although he did not arrive aboard her until 28 August. He was almost immediately sent on a speaking tour to influence American public opinion, until he was recalled home in October and relieved by Captain A. G. Talbot on 1 October. The work was completed in November and "Illustrious" departed on 25 October, for trials off Jamaica and to load the dozen Swordfish of 810 and 829 Squadrons. She returned to Norfolk on 9 December, to rendezvous with "Formidable", which had also been repaired there, and the carriers sailed for home three days later. On the night of 15/16 December, "Illustrious" collided with "Formidable" in a moderate storm. Neither ship was seriously damaged, but "Illustrious" had to reduce speed to shore up sprung bulkheads in the bow and conduct temporary repairs to the forward flight deck. She arrived at Greenock on 21 December and permanent repairs were made from 30 December to late February 1942 at Cammell Laird's shipyard in Birkenhead. While working up her air group in March, reinforced by the Grumman Martlet fighters (the British name of the F4F Wildcat) of 881 and 882 Squadrons, she conducted trials of a "hooked" Supermarine Spitfire fighter, the prototype of the Seafire.