In an attempt to strengthen their defensive positioning for their empire in the South Pacific, Japanese forces decided to invade and occupy Port Moresby in New Guinea and Tulagi in the southeastern Solomon Islands. The plan to accomplish this, called Operation MO, involved several major units of Japan's Combined Fleet, including two fleet carriers and a light carrier to provide air cover for the invasion fleets, under the overall command of Japanese Admiral Shigeyoshi Inoue. The U.S. learned of the Japanese plan through signals intelligence and sent two United States Navy carrier task forces and a joint Australian-American cruiser force, under the overall command of American Admiral Frank J. Fletcher, to oppose the Japanese offensive.