Pearl Harbor Advance-knowledge Conspiracy Theory - Allied Intelligence

Allied Intelligence

Locally, Naval Intelligence in Hawaii had been tapping telephones at the Japanese Consulate before the 7th. Among much routine traffic was overheard a most peculiar discussion of flowers in a call to Tokyo (the significance of which is still publicly opaque and which was discounted in Hawaii at the time), but the Navy's tap was discovered and removed in the first week of December. The local FBI field office was informed of neither the tap nor its removal; the local FBI Agent in charge later claimed he would have had installed one of his own had he known the Navy's had been disconnected.

Throughout 1941, the U.S., Britain, and the Netherlands collected considerable evidence suggesting Japan was planning some new military adventure. The Japanese attack on the U.S. in December was essentially a side operation to the main Japanese thrust to the South against Malaya and the Philippines—many more resources, especially Imperial Army resources, were devoted to these attacks as compared to Pearl Harbor. Many in the Japanese military (both Army and Navy) had disagreed with Admiral Isoroku Yamamoto's idea of attacking the U.S. Fleet at Pearl Harbor when it was first proposed in early 1941, and remained reluctant after the Navy approved planning and training for an attack beginning in spring 1941, and through the highest level Imperial Conferences in September and November which first approved it as policy (allocation of resources, preparation for execution), and then authorized the attack. The Japanese focus on South-East Asia was quite accurately reflected in U.S. intelligence assessments; there were warnings of attacks against Thailand (the Kra Peninsula), Malaya, French Indochina, the Dutch East Indies (Davao-Weigo Line), the Philippines, even Russia. Pearl Harbor was not mentioned. In fact, when the final part of the "14-Part Message" (also called the "one o'clock message") crossed Kramer's desk, he cross-referenced the time (per usual practice, not the brainwave often portrayed) and tried to connect the timing to a Japanese convoy (the Thai invasion force) recently detected by Admiral Hart in the Philippines.

The U.S. Navy was aware of the traditional planning of the Imperial Japanese Navy for war with the U.S., as maintained throughout the 1930s and into the 1940s. The Japanese made no secret of it, and in the 1930s American radio intelligence gave U.S. war planners considerable insight in Japanese naval exercises. These plans presumed there would be a large decisive battle between Japanese and U.S. battleships, but this would be fought near Japan, after the numerical superiority of the U.S. Pacific Fleet (assured by the Washington Naval Treaty, and still taken as given) was whittled down by primarily night attacks by light forces, such as destroyers and submarines. This strategy expected the Japanese fleet to take a defensive posture, awaiting U.S. attack, and it was confirmed by the Japanese Navy staff only three weeks before Pearl Harbor. In the 1920s, the decisive battle was supposed to happen near the Ryukyu islands; in 1940 it was expected to occur in the central Pacific, near the Marshall islands. War Plan Orange reflected this in its own planning for an advance across the Pacific. Yamamoto's decision to shift the focus of the confrontation with the U.S. as far east as Pearl Harbor, and to use his aircraft carriers to cripple the American battleships, was a radical enough departure from previous doctrine to leave analysts in the dark.

There had been a specific claim of a plan for an attack on Pearl Harbor from the Peruvian Ambassador to Japan in early 1941. (The source of this intelligence was traced to the Ambassador's Japanese cook. It was treated with skepticism, and properly so, given the nascent state of planning for the attack at the time and the unreliability of the source.) Since Yamamoto had not yet decided to even argue for an attack on Pearl Harbor, discounting Ambassador Grew's report to Washington in early 1941 was quite sensible. Later reports from a Korean labor organization also seem to have been regarded as unlikely, though they may have had better grounding in actual IJN actions. Apart from the documents mentioned, there has been uncovered no record of a serious belief or conviction by anyone in U.S. or UK military intelligence (in Hawaii, DC or elsewhere), or among U.S. civilian policy officials, prior to the attack, of Pearl Harbor or the U.S. West Coast as a potential target.