This map shows the Pacific theater of war in 1942. Notice all the islands north and west of Australia, and out in the middle of the ocean between Australia and Japan? All these tiny islands were very important to both the U.S. and Japan during World War II. These islands were places where air fields could be built to launch air attacks. Some of them had fuel stations to refill aircraft carriers. All of them were like stepping-stones to bigger targets. The Mariana Islands are a good example. They are on the far right of this map. They are very strategically located. If the U.S. occupied the Marianas, it could use them as a base for air attacks on Japan or the Philippines. Like the Marianas, Guadalcanal was another strategically located island. From there, the Japanese could attack Australia. These photos show the airfield the Japanese were building at Guadalcanal when the U.S. invaded the island in 1942. Island-hopping was a long and deadly process. First, the invading U.S. forces would have to land on an island while the Japanese fired at them. Here U.S. Marines land at Guadalcanal on August 7, 1942. To stop the U.S. aircraft carriers from landing soldiers on the island, the Japanese would send fighter planes to bomb the carriers. The USS Enterprise is being attacked here. After the U.S. soldiers gained a foothold on the beach, they had to slowly fight their way inland. Japanese soldiers would be hidden throughout the forests of these tropical islands. These Marines crossing a river are a perfect target for Japanese fire. Usually it took weeks or even months of fierce fighting to weaken the Japanese to the point where they could no longer fight. Terrible battles were fought on every island. Most Japanese soldiers would not surrender to Americans. They were determined to die in battle or, if they could no longer fight, to commit suicide. Here American Marines pull out the bodies of Japanese soldiers who killed themselves in their bunker. When things were quiet, U.S. soldiers could never be sure if it was because all the Japanese soldiers were dead, or if they were just hiding in bunkers, waiting to attack when the Americans let their guard down. American soldiers used dogs to locate hidden Japanese bunkers and raid them. It was deadly work: Sometimes the bunkers did hold Japanese soldiers ready to fight. At last Guadalcanal was conquered, and the U.S. could finish the airfield the Japanese had started, and use it to attack Japanese targets.