for nearly half that time. On 18 April, naval planning accorded the Eastern Fleet the highest priority for reinforcement, which also included transferring most of the carriers from the Home Fleet and the Mediterranean, with the intention of returning to Ceylon in September. By June, Ceylon was defended by three RAF squadrons (64 aircraft, plus reserves), three strike squadrons (including one of Beauforts), and much improved radar and anti-aircraft defences. Ground defences were manned by two Australian army brigades. The invasion scare was short-lived. British intelligence detected the movement of the Japanese carrier force eastward in mid-April, and their deployment in the Pacific in mid-May. After the Battle of Midway in June, it was realized that there was no longer the threat of major Japanese naval activity in the Indian Ocean. In September, British intelligence predicted Japan would go over to the defensive. As a result, the Eastern Fleet was not reinforced as planned and, instead, shrank after early July. Japanese reaction The Japanese did not exploit their victory as the British feared. The decision to postpone major operations in the Indian Ocean was upheld. The Japanese aircraft carriers required maintenance and replenishment after months of intensive operations, and there was already difficulty in maintaining the strength of frontline air units. Nagumo and officers such as Mitsuo Fuchida (commanding Akagi's air group) felt that the losses inflicted on the British did not justify the loss of experienced Japanese air crews. Japanese attention also lay elsewhere. In early May, Japanese carriers fought the Battle of the Coral Sea in the southwest Pacific, followed in June by the Battle of Midway. In both cases, losses constrained Japanese options further. In June, the IJA developed a plan for a major offensive in the Indian Ocean, including an invasion of Ceylon. The Germans were advancing in North Africa, which made an Axis link-up in the Middle East attractive. Resource constraints forced the IJN to reject it, especially once the Guadalcanal Campaign started. Subsequently, the limit of Japanese operations in the Indian Ocean was against trade using submarines and armed merchant cruisers. Notably, a submarine group patrolling off East Africa attacked the harbour at Diego-Suarez, Madagascar, while the Allies were capturing the island. Ironically, the Allies were motivated by fears that the Japanese might establish a base there to attack trade. Overall, Japanese attacks on trade enjoyed some success, but after 1942 the presence of