Everyone knows that the codebreakers of Bletchley Park broke the German ciphers, giving Churchill and his generals an unparalleled view inside Hitler’s command post and cutting as much as two years off the end of the Second World War. That story is told in full in Biteback’s The Secrets of Station X. But even now very few people realize that by the time of D-Day in June 1944, a substantial proportion, possibly even the majority, of people at Bletchley were working not on German ciphers but on Japanese codes.
It has always been assumed that the Americans broke the Japanese codes and ciphers. This is partly because there has never been the same interest in the war in the Far East here in the UK as there is in America. It’s true that British troops fought the Japanese in Malaya and that tens of thousands of British soldiers captured by the Japanese were treated appallingly. Yet the British never felt quite so threatened by the Japanese as they did by the Germans who were just across the Channel waiting to invade.
The assumption that the Americans broke the Japanese codes was largely due to the fact that the first stories of the amazing achievements made by British and US codebreakers during the Second World War were published in America and dealt with US exploits against the Japanese, a much more immediate war for the US people given the successful attack on Pearl Harbor.
It was only when GCHQ started releasing its files in large numbers in the late 1990s that we began to realise the extent of the British involvement in breaking the Japanese codes. The main army messages were first encoded and then the encoded text was enciphered using streams of randomly generated figures. Yet John Tiltman, one of the greatest of the Bletchley Park codebreakers, managed not just to work out what the code and cipher system was but to break it within a few months of its introduction.
When the Japanese navy went over to a similar system with its main code, JN-25, Tiltman broke it within weeks. All of that information was shared with the Americans and it was a similar story with most of the other Japanese codes and ciphers. But while the British made the initial breaks into all the main Japanese military and naval codes and ciphers, it was the Americans who were better at keeping on top of the codes and ciphers, using large numbers of machines and personnel.
The work against the Japanese codes and ciphers was not dominated by either country, it was a truly collaborative story and now for the first time that story can be read in e-book form in The Emperor’s Codes.