Yamamoto thought that another attack on the U.S Naval base at Pearl Harbor would make all of the American fleet to sail out to fight, including the carriers. However, because of the many American land-based airplanes on Hawaii, he thought that it was too risky to attack directly. Instead, he decided to attack Midway, a tiny atoll at the northwest end of the Hawaiian Island chain, approximately from Oahu. The Japanese didn't need Midway but they felt the Americans would try hard to defend it.