October-December 1941: Canada Decodes Latin American Messages

"Americans in Britain: the Training of the Civilian Technical Corps at RAF Radio School, Cranwell, England, 1941," Image: IWM (D 5286). Imperial War Museum Collections, https://www.iwm.org.uk/collections/
item/object/205198855.

On the previous page, we saw how the Canadian military continuously adapted protections on their wireless communications throughout the war, applying their own expertise in intercepting enemy and neutral communications to defending against potential enemies doing the same sort of signals intelligence work. In the summer of 1941, the Canadian military considered the relative security of various wireless communications technologies, and of different codes and ciphers that could be used to protect communications. We have already seen that Canadian knowledge of what sorts of radio telephony—even low-powered R/T—could be intercepted by enemies across the ocean came from Canada’s own efforts to intercept enemy wireless communications. This page explains how Canada’s knowledge of what kinds of codes and ciphers would provide the best security for military communications was not only theoretical, but it too came from a Canadian offensive intelligence effort—in this case, that of decoding enemy and neutral intercepted messages.

An important aspect of wireless interception was making intercepted messages readable. The Canadian signals intelligence operation during the Second World War relied on the expertise of people who could break codes, and those who could translate foreign languages. Although at first, most of this specialized work was done in Britain, during the war the Canadians gained more expertise and began to process more intercepted messages themselves. In late 1941, part of keeping an eye on the Americas meant decoding Latin American intercepts, and sharing the intelligence gathered with the Department of External Affairs and with Washington.

On October 7th, 1941, Brigadier H.F.G. Letson, Military Attaché of the Canadian Legation in Washington, D.C. wrote to the Director of Military Operations and Intelligence at N.D.H.Q. with inquiries from the U.S. F.C.C. about Canada’s monitoring of Central and South American radio stations. On this day, the Canadians had decided to officially inform the U.S. F.C.C. that Canada was not only engaging in the type of radio monitoring the F.C.C. was jointly responsible for with the F.B.I., but that the Canadians were also “engaged, on a limited scale, in monitoring unfriendly stations outside the North American Continent” (CDWI00208). By this time, the foreign policy of the still-neutral U.S. was growing ever-more hostile towards Germany and Japan, and it seemed as though the United States would eventually have to be brought into the fold of Allied global signals intelligence. The Canadians were doing their part to ease this transition by strategically revealing hints of how large Allied wireless interception efforts had already grown in just two years.

The Canadians were already trying to establish a relationship of exchanging foreign signals intelligence with the United States, asking for the Americans’ intercept data on certain foreign stations, and offering to share Canada’s work on these transmissions as a gesture of good faith, whether or not the Americans followed through on their end. Brigadier Letson reported back to N.D.H.Q. that “It is felt that this [gesture] has created a good impression and should open the way to greater cooperation in the future” (CDWI00208). The Canadians also revealed in an October 7th meeting in Washington that Canada had broken some of the ciphers used by South American stations. The Canadian strategy of giving the Americans a taste of Canada’s foreign signals intelligence capacity proved effective, and it led the Americans to assume that Canada had even more prowess in the realm of wireless interception than was actually the case.

The F.C.C., thoroughly convinced that any descriptions of the “limited scale” of Canadian intelligence operations involved some degree of false modesty, asked Ottawa to “assist with [their] D.F. [direction finding] equipment in radiolocation work by U.S. stations” in the future (CDWI00208). The Canadian representative at these meetings, Major Drury, did not admit at that time that, in fact, Military Intelligence had no such direction finding stations, and was still entirely reliant on the Navy for determining the origins of wireless broadcasts (CDWI00209).

On October 20th, 1941, a response made its way from N.D.H.Q. in Ottawa to the Canadian Legation in Washington. The letter answered some of the queries the Americans had posed, and instructed Brigadier Letson to assure the Americans that Canada would be “glad to afford [the F.C.C.] all the co-operation we can in [direction finding]” with the small caveat that this co-operation would have to wait for at least another two months while Canadian Military Intelligence set up their first two independent direction finding stations. The Director of Military Operations and Intelligence complained in his letter to Washington that “At the moment we rely entirely on the Navy for any D.F. work; and since that service is continuously employed on its own operations, it is sometimes difficult to get a response from them to any requests we may have” (CDWI00209).

The Colonel’s October 20th letter also permitted Letson to reveal that Canadian intelligence had broken the ciphers of Central and South American “Gestapo” stations, and these secret enemy messages were “being read” in Ottawa (CDWI00209). Sharing information about Canada’s signals intelligence network with the Americans proved fruitful on October 22nd, 1941 when another letter from Brigadier Letson in Washington arrived at N.D.H.Q., illuminating the American system of wireless interception and intelligence more fully. The Canadians learned from this letter that the U.S. F.C.C. was responsible only for interception when it came to foreign radio broadcasts, and sent these raw, unprocessed messages on to the F.B.I., which handled the work of deciphering and acting on the intelligence produced. So while the F.C.C. would be glad to continue to receive any intercepted messages from American amateur or illegal radio stations, if the Canadians wanted to co-operate on the interception of South and Central American broadcasts, they would have to go through the F.B.I. (CDWI00210).

The Canadians’ main focus when it came to intercepting southern communications was in revealing relays in Central and South America, which were used to facilitate long-distance wireless communication between Germany and Japan. Other stations were run by German spies in South America, and these were known colloquially to Canadians and Americans as ‘Gestapo stations’ (as we read above). However, some of the intercepted broadcasts were also destined for or originating from South American countries themselves, some of which still maintained economic relationships with Germany or Japan.

The following episode is one example of the kind of traffic coming from ‘Gestapo stations’ in South America, and is related in my other briefing book, Wireless Weirdness:

On December 3rd, 1941, a coded message was sent from Rio de Janeiro, Brazil to Hamburg, Germany. The Canadians intercepted the message and by December 8th it had been deciphered and sent on to Washington, D.C.

By that time, the United States had been drawn into the Second World War by a Japanese surprise attack against Pearl Harbor on December 7th.

The intercepted message (which is unfortunately missing from this collection) referred to the locations of United States battleships, as well as the number of transports seen off the coast of South America with cruiser escort. The U.S. Navy was being watched closely, and that information had presumably made its way to Germany.

Naturally, the Canadians sought to inform the U.S. of this suspicious broadcast, possibly feeling increased urgency to get this message into the hands of U.S. intelligence in the wake of the shocking preemptive strike by the Japanese.

By December 22nd, the Americans had sent a grateful reply back to Ottawa. The Office of Naval Intelligence in Washington had received the Canadian intercept and fact-checked it. It is understandable that this office may have had a busy couple of weeks and could not immediately respond to the Canadian shared intelligence. Unfortunately, U.S. intelligence concluded that the Brazilian telegram was “partially correct” in its observations of American vessels, although other claims it presented were “obviously untrue” according to the Americans (CDWI00231).

For an example of a message between Japan and South America the Canadians intercepted and read, see CDWI00230:

In late December 1941, Rockcliffe intercepted a Japanese message from December 8th which they thought would be of interest to Washington. It was destined for La Paz, Bolivia, informing the recipient that a Mr. Kawachi, who was a mining engineer with the Japanese Department of Overseas Affairs, had flown into Arequipa, Peru that morning and would be in Bolivia soon (CDWI00230).

Throughout the war, Canada spied on foreign wireless communications across the Americas, and had some success breaking diplomatic and other codes. It is unclear in these early stages of the war how much of the codebreaking innovation was done in Ottawa, and to what extent reconstructed codebooks and cryptanalytic techniques were imported from Britain. It is clear, however, that the experience of Canadian Military Intelligence in intercepting and decrypting enemy communications led to a better understanding of how Canada could defend its own communications against similar efforts by the Germans or Japanese. The way Canada knew how best to defend itself came from its experience as an attacker. That kind of practical knowledge could only be gained by being on the forefront of the global signals intelligence game. Additional sources about Canadian codebreaking during the Second World War can be found in the Further Reading tab of this briefing book.