Guadalcanal was the first battle in the American amphibious campaign to liberate the Pacific from Japanese occupation. Although the naval battles of Midway and Coral Sea have been described as the turning points, in the Pacific War, Guadalcanal was where the Japanese war machine was finally halted. Both Japanese and American forces fought the battle (one of the longest in the Pacific War) at the farthest end of their respective supply lines and in a terrain and climate that was hostile to both sides. Both sides also lost large amounts of ships off the island, so much so that it became known as 'Iron Bottom' Sound. As one can guess, the burden of much of the battle was carried by the United States Navy and the US Marine Corps, although later on, a substantial number of US Army units joined the fight. The first unit to be engaged on Guadalcanal was the newly formed 1st Marine Division, which had moved from the east coast of the United States to Wellington, New Zealand on 14th June 1942.
Meanwhile the Japanese had continued to advance to the north coast of New Guinea and onto the Admiralty Islands, the Solomon Islands and pushed south seizing Tulagi and Guadalcanal, where they started construction of an airfield. The continued Japanese advance threatened the lines of communications from the United States to Australia and New Zealand. It also put a number of US bases in danger and so the Joint Chiefs of Staff came to the conclusion that an offensive in the Pacific was now vital. The 1st Marine Division was given the task of seizing Guadalcanal and the partially built airfield.