Australian Coastwatchers, volunteers left behind Japanese lines, informed the Allied command that the Japanese were building an airstrip on Guadalcanal in late spring of 1942. At the time, the Allies were reeling from unchecked Axis advance in the Pacific and Europe. The airstrip could threaten Allied installations in the Hebrides, Fiji, New Caledonia, and eventually could threaten Australia itself. Clearly a response was needed.
Army Gen. Douglas MacArthur, and Navy Pacific Fleet Admiral Chester W. Nimitz, squabbled over who would direct the Guadalcanal campaign. Eventually the command areas were redrawn so Nimitz was in command of the overall operation.
Hastily drawn up plans took the 1st Marine Division, commanded by Gen. Arthur Vandergrift, from US ports on the west and east coasts to Australia and their staging area in Wellington, New Zealand. This was the largest Marine unit ever assembled. They did not have time to "combat load" – put equipment on their transports in reverse order of how it would be taken off – any of their transports. Combined with operations by Marine raiders and paratroopers on surrounding islands, they attacked Guadalcanal on August 7, 1942. They met little resistance from a shocked Japanese garrison, which fled the airstrip. Once taken by the Americans on the first day, they never let it go.