 Two days later, they attacked Christmas Island and "Hiryū"s aircraft sank the Dutch freighter "Poelau Bras" before returning to Staring Bay on 11 March to resupply and train for the impending Indian Ocean raid.This raid was intended to secure newly conquered Burma, Malaya, and the Dutch East Indies against any Allied attack by destroying base facilities and forces in the eastern Indian Ocean.On 26 March, the five carriers of the First Air Fleet departed from Staring Bay; they were spotted by a Catalina about southeast of Ceylon on the morning of 4 April.