On the "Kidō Butai's" return journey from Pearl Harbor, IJN carriers "Soryu" and "Hiryu" and their supporting screen split off from the main group and went to Wake Island to support Japan's invasion there. From there, they went to Ambon Island in the Dutch East Indies and bombed it as part of a Japanese operation to isolate resource-rich Java. The other four fleet carriers returned to Japan's Inland Sea. From there, they sortied south to support the invasion of New Britain, enabling the establishment of a powerful Japanese naval base at Raboul. "Soryu" and "Hiryu", along with light carriers "Zuiho" and "Ryujo", supported the invasion of raw material-rich Java. The USS "Langley", America's first aircraft carrier but then serving as a seaplane tender, was delivering planes to Java during this period. In February, it was sunk by Japanese bombers with 32 badly needed Allied planes aboard. Darwin, the only Australian base from which Java could be supported, was bombed to prevent interference with Japan's invasion of Java. A total of 188 carrier-launched planes from "Akaga", "Kaga", "Hiryu", and "Soryu", along with 54 land-based aircraft from recently conquered Kendari and Ambon Island, sank eight ships, seriously damaged nine others, and destroyed 18 Allied planes and the airfield at a cost to Japan of only two planes lost. By the end of March with complete control of the air, the Japanese navy defeated Allied naval forces near Java thereby permitting large numbers of Japanese troops to land and ultimately secure oil fields for use by the Empire. The Greater East Asia Co-Prosperity Sphere envisioned by Japanese planners had now been established. The next steps were to establish a strong military perimeter from which to defend these valuable conquests.