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The impact of Bletchley Park’s Japanese codebreaking operation on World War Two was just as significant as their work on German ciphers. In close cooperation with the Americans, thousands of codebreakers at Bletchley Park and outposts in India and across the Indian Ocean targeted Japanese naval, military and diplomatic signals. Efforts intensified in the latter years of WW2 and particularly after VE Day, when many staff who had been working on German ciphers were retrained for Japanese codebreaking. The intelligence gained through this US / UK partnership turned the tide of the war in the Pacific, paving the way to Japan’s surrender.


This album was first published on 15 August 2020 on what was the 75th anniversary of Victory over Japan (VJ) Day.

Japan used many encryption systems during the course of World War Two, including numerical ciphers, such as the Japanese Navy’s General Operational Code (JN25).  Bletchley Park’s codebreakers used statistical methods to decrypt numerical ciphers but even the decrypted messages were difficult to read. They were full of codenames and abbreviations. Tools such as this list of abbreviations commonly used by the Japanese Navy helped translators make sense of the message content.

This is one of a series of flashcards used in Japanese language training. A working knowledge of Japanese was essential for translating Japanese messages, but Japanese speakers were in short supply. Captain Oswald Tuck, a retired Naval captain who had lived in Japan, was tasked with setting up a condensed language course that could equip Bletchley Park staff with a sufficient working knowledge of Japanese in as short a time as possible. The eleven-week course Tuck devised was so successful that it ran throughout the war. Graduates of Tuck’s Bedford Japanese School went on to work as translators at Bletchley Park, in East Asia, Australia and the USA.

LAC Jack Kinsey was a wireless intercept operator against Japanese traffic at the Wireless Experimental Centre (WEC), on the outskirts of Delhi. The WEC was one of a number of overseas outposts of Bletchley Park. It was the main British operation for intercepting Japanese military codes and ciphers in WW2, covering wireless interception, traffic analysis and direction finding, codebreaking, and intelligence collation and reporting. This snapshot of Kinsey and his colleagues is from his wartime photograph album, recently donated to Bletchley Park.

Also working as a wireless intercept officer was Wren Susan Fellowes (nee Broadhurst-Hill). She left England on 16 December 1943, bound for Colombo, in Ceylon (now Sri Lanka). The photograph shows her accommodation while working at the Far East Combined Bureau, another of Bletchley Park’s overseas signals intelligence centres, taking down Japanese Naval signals:

This excerpt is from a series of Far Eastern Summary Reports that collate Ultra intelligence gained from intercepted Japanese messages. Summary number 8 includes information on Japan’s monthly production of aircraft, the reopening of bombed railway bridges in Hanoi, Japanese order of battle, and instructions from the Southern Army in Manila to forces in New Guinea to discontinue the use of “special smoke shells, self-exploding bottles and similar weapons” so as not to provoke a chemical attack from the enemy.

By the end of the war, the Allies had amassed a wealth of detailed intelligence about Japanese forces. This map, showing the locations of Japanese Naval Air Commands in August 1945, is taken from a report stamped ‘Top Secret Ultra’. Compiled on 20 September 1945, the report lists the “Organization, locations of command headquarters and subordination of units of the Japanese Army & Navy Air Forces”, based on information gathered up to August 1945.

In a typescript memoir, Hugh Norris, a Japanese translator in Naval Section at Bletchley Park, recalls hearing of the atom bombs dropped on Hiroshima and Nagasaki. He goes on to reflect on the abrupt cessation of work at Bletchley Park following VJ Day. “In retrospect, Bletchley did not seem to us at the time to be at all strange, once we had experienced a few weeks of initiation; it very soon became part of our lives; it was normality itself, and it seemed as if it was set to go on for ever. What was unnerving was when everything stopped so abruptly: it was the world outside, to which we now had to adapt, that was strange and foreign.”

Veteran Joan Smeaton, née Addison, travelled to London to celebrate VJ Day with her fellow Wrens. After VE Day, she had been sent to retrain in Japanese Morse code. Joan was then posted to Flowerdown, a Royal Navy intercept station near Winchester, to work as an intercept operator for Japanese messages. “We were there when the War ended and we hitched up to London for the celebrations. We just stood at the side of the road in smart uniform and waited for a lift. You were never alone of course, usually in groups of two or three. I recall once that friends of ours had managed to get a lift in a lorry and there was me and my friend Sheila left on the roadside when a long sleek limousine drew up with two American Naval Officers in the back. They were going up to London and gave us a lift. We passed our friends in the lorry on the way!”

Veteran John Statham of Bletchley Park’s Naval Section recalls the codebreaking operations being wound up after VJ Day:  “I was at Bletchley until it was finally closed … I remember things going up in smoke and the huts being trashed really. Well I say trashed, everything being torn up. It was such a sad time somehow. We were chucking stuff on bonfires and things like that. I remember “freeing” a typewriter from one of the Huts because all of the typewriters and the equipment were being chucked away. I freed this great big hefty thing which I kept for about a year but it was too hefty to go around. But if I hadn’t freed it, it would have gone on a bonfire or something.”

Wrens at the Far East Combined Bureau in Colombo, Sri Lanka, like Dot Tuffin (née Wilkinson), who had been working on Japanese codebreaking, were asked to volunteer to stay on after VJ Day to help acclimatise returning prisoners of war. “This was an entirely different aspect to our work, we just volunteered; the men looked pretty dreadful and we just wanted to help these men. It was harrowing for us; my friend and I cried ourselves to sleep every night – we couldn’t believe they could even walk, they looked so awful. The men came through in three to 4 weeks; we were told we had done our jobs, thank you very much, and we had to go back to Woburn Abbey to be demobbed.”

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