On 7 August 1942 , Allied forces ( primarily U.S. ) landed on Guadalcanal , Tulagi , and Florida Islands in the Solomon Islands . The landings on the islands were meant to deny their use by the Japanese as bases for threatening the supply routes between the U.S. and Australia . They were also intended to secure the islands as starting points for a campaign to neutralize the major Japanese base at Rabaul and support the Allied New Guinea campaign . The landings initiated the six @-@ month @-@ long Guadalcanal campaign .