Answer: He tried to deliver a heavy blow to put Japan in a good position at the start.
Step-by-step explanation:
By attacking Pearl Harbor, Yamamoto sought to surprise the United States. He thought it was the only way for Japan to deal with the enemy. With a sudden attack, he tried to damage the United States fleet and make Japan the strongest naval power in the Pacific Ocean. Yamamoto considered this to be Japan’s only chance in the war. He also thought that an attack on Pearl Harbor would force American diplomacy to negotiate with Japan, in conditions in which that Asian country would dictate the terms of peace.