<P> Because of the severe losses in carriers at Midway, the Japanese were unable to support another attempt to invade Port Moresby from the sea, forcing Japan to try to take Port Moresby by land . Japan began its land offensive towards Port Moresby along the Kokoda Track on 21 July from Buna and Gona . By then, the Allies had reinforced New Guinea with additional troops (primarily Australian) starting with the Australian 14th Brigade which embarked at Townsville on 15 May . The added forces slowed, then eventually halted the Japanese advance towards Port Moresby in September 1942, and defeated an attempt by the Japanese to overpower an Allied base at Milne Bay . </P> <P> In the meantime, the Allies learned in July that the Japanese had begun building an airfield on Guadalcanal . Operating from this base the Japanese would threaten the shipping supply routes to Australia . To prevent this from occurring, the U.S. chose Tulagi and nearby Guadalcanal as the target of their first offensive . The failure of the Japanese to take Port Moresby, and their defeat at Midway, had the effect of dangling their base at Tulagi and Guadalcanal without effective protection from other Japanese bases . Tulagi and Guadalcanal were four hours flying time from Rabaul, the nearest large Japanese base . </P> <P> Three months later, on 7 August 1942, 11,000 United States Marines landed on Guadalcanal, and 3,000 U.S. Marines landed on Tulagi and nearby islands . The Japanese troops on Tulagi and nearby islands were outnumbered and killed almost to the last man in the Battle of Tulagi and Gavutu--Tanambogo and the U.S. Marines on Guadalcanal captured an airfield under construction by the Japanese . Thus began the Guadalcanal and Solomon Islands campaigns that resulted in a series of attritional, combined - arms battles between Allied and Japanese forces over the next year which, in tandem with the New Guinea campaign, eventually neutralized Japanese defenses in the South Pacific, inflicted irreparable losses on the Japanese military--especially its navy--and contributed significantly to the Allies' eventual victory over Japan . </P> <P> The delay in the advance of Japanese forces also allowed the Marine Corps to land on Funafuti on 2 October 1942, with a Naval Construction Battalion (Seabees) building airfields on three of the atolls of Tuvalu from which USAAF B - 24 Liberator bombers of the Seventh Air Force operated . The atolls of Tuvalu acted as a staging post during the preparation for the Battle of Tarawa and the Battle of Makin that commenced on 20 November 1943, which was the implementation of Operation Galvanic . </P>

Why did the battle of coral sea start