Did the Allies know about the Japanese intention to attack Pearl Harbor?

Answer 1

No, not really. The specific Japanese plans to attack the US Air & Naval Bases at Hawaii were very secret, as were the Japanese plans to attack Wake Island, Guam, the Philippines, the Dutch East Indies, Malaya, Burma, Hong Kong and the Gilbert Islands. As tensions increased between the US & Britain with Japan, from mid-1940 onward, the United States & Britain increased military defenses across the Pacific. The US & Britain each considered it very likely that, if war came, then the Japanese would strike Malaya, Singapore, Burma, the Philippines, the Dutch East Indies, and Wake Island. The United States fleet moved from San Diego, California to Pearl Harbor, Hawaii in June 1940 to serve as a warning to the Japanese to refrain from aggressive actions in the Pacific. Although the United States had mostly broken the Japanese diplomatic code, it could not read messages by the Japanese military (army or navy). The US & Britain knew that Japan intended to go to war with them, but not specifically when, or where the attacks would come. Also the US & British watched Japanese shipping & troop movements in the ocean south of Japan, to help determine about the timing of Japanese attacks in that area. In the first week in December 1941, it was looking like war was about to come within a few days or a week. On December 6, intercepts of Japanese diplomatic code lead US naval & army intelligence to believe that war was now just hours or days away. There was still no way to know for sure where the Japanese would attack. Remember Japanese diplomats had no access to Japanese military plans, and reading their messages would not help determine targets. The US Military planners believed the Japanese would attack the US in the Philippines, Guam and Wake Island. However there was not any real thought that Japan would attack Hawaii to start the war. Possibly because of the great distance & time need to travel from the nearest Japanese naval bases in Japan. In my opinion, the primary US failure at Pearl Harbor was the mistaken belief that Pearl Harbor was outside the danger zone for any large surprise Japanese attack. This was a failure on the most part by the local US commanders (Admiral Kimmel & General Short) in Hawaii, as evidenced by their shortcomings in defensive preparations, especially against air attack. The navy had taken some measures to protect the harbor from submarines. The army was most concerned about sabotage from Japanese living in Hawaii. So, in the end, the Japanese surprise attack on Pearl Harbor on December 7, 1941 was a surprise to the local US forces and a surprise to US leaders in Washington, DC. The surprise was not that Japan was going to atack, just where!