Pearl Harbour

In March 1986 an Ottawa news headline read “Japanese cables could have provided advance warning of Pearl Harbour”.[1] This shocking headline was a direct result of the newly available information on the Examination Unit.

The British and Canadian governments had worked out that Canada's cryptographic unit would focus on decrypting the Japanese and French Vichy governments' communications.[2] As a result the Examination unit was decoding and compiling information on Japan's activities. There were a few factors that lend to the sensational headline and the belief that the allied governments had advance knowledge of the attack on Pearl Harbour (pictured below).

Decoded Diplomatic Messages

Canadian communications intelligence collection focused on diplomatic messages from Japanese foreign officers present in North and South America. The examination unit had been monitoring the Japanese diplomatic traffic since its inception in June of 1941.[2] In October of that year, Tojo Hideki was elected the PM of Japan and the country's expansionist policies increased in intensity. The diplomatic messages showed that the Japanese were increasingly concerned with being seen as a warmonger by the allied powers and the US. One example of this is the following message from a Japanese diplomat in Washington to Tokyo, who warns of the potential ramifications of the new Tojo government's policies:

“The new Premier's policy of seizing with lightning speed the opportunity of expansion in all directions, without distinction between North and South, will be dangerous. If Japan wishes to maintain the “status quo” in the Far East, the situation will not be changed. The policy of the new cabinet should avoid anything of a radical nature”[1]

Another example from a Japanese diplomat in Canada:

“The outcome of the (Japanese) war party’s policy will, in all likelihood, bring England and the U.S.A. into the war. … The determined policy of Japan, while not voiced, is based on their firm belief in the power of their navy. Canada deems it necessary to arm itself in preparation for eventualities in the Pacific.” [1]

The diplomatic telecommunications showed that the Japanese government in Tokyo was well aware that its expansionist policies would inevitably draw the British, their dominions, and US into the war. Yet the Japanese government continued its policy, knowing all well that it would inevitably bring in the allied powers into war with them.

It is in this context that we can see how Japan might have felt that in order to continue to pursue its expansion the US would inevitably be drawn into the conflict, and that it was only a matter of when, and who would have the upper hand then. This, as well as the Japanese policy of “first attack being honourable”, inform japan’s decision to bomb pearl harbour. [1]

Meeting at Chateau Laurier

On 1 December 1941 at the Chateau Laurier Hotel in Ottawa the head of a pilot recruitment (Mr. Seymour) program met with a close friend who worked compiling examination unit intel. In a sworn affidavit Mr. Seymour recounted that his friend;

“informed [him] that British and Canadian Military Intelligence suspected that the Japanese would make a surprise air attack on Pearl Harbour on December 8th, 1941. . . . [which] meant that the United States immediately would be involved in War with Japan, [and] would probably become involved in the War with Germany and Italy.” [1]

Many years later when telling his story and investigating why the Allies had "let the attack happen his close friend Lester B. Pearson privately wrote:

“As for the truth of the story that ‘British Military Intelligence’ were able to state on December 1, 1941 that Pearl Harbour would be attacked on December 8, there is nothing that I have been able to find in the records of anyone having firm intelligence about the date. But the British (and the Americans, and Canadians) seem to have had enough communications and other intelligence at hand at that time to expect that an attack would be made in the near future on Pearl Harbour, quite possibly in 29 early December.” [1]

Regardless of the initial statements between Mr. Seymour and his close friend, the statement from Lester B. Pearson (made while he was PM) shows that the information decoded by the Examination Unit meant that there was a high degree of knowledge of Japanese war activity.

Decrypting Japanese Naval Movements

On 6 December, the Examination Unit decrypted a message that had been sent on the 3rd of December 1941 by the South American German spy network. It reported that Japan was mobilizing a large group of troops and ships into further south-east into the pacific. [1]

As of December 6th Canada and its allied were aware that Japan was moving battle troops to the south and into the US controlled seas. The US and British intelligence efforts were informed immediately. Apparently, the German message prompted the head of the examination unit to hold a meeting the next day, in the morning of 7 December, so that a war declaration speech could be drafted.[2] Pearl harbour was attacked on that afternoon.

This information does not in anyway delegitimize the fact that Japan attacked a state it was not at war with, nor does it shift the blame of the loss of life at pearl harbour away from Japan. These facts do show that the though the public was shocked, the allied governments were likely aware that a surprise a tack was imminent in the days leading up to Pearl Harbour.