During World War II, the Japanese built tunnel and bunker systems in and on Mount Suribachi. In February 1945, United States Marines invaded the island and initiated a major battle. For the United States, Iwo Jima was an important strategic point between the United States and mainland Japan, needed as an airstrip for damaged B-29s returning to the Mariana Islands from bombing Japan, a status that resulted in severe fighting that took the lives of nearly 7,000 Americans and 20,000 Japanese.