The Emperor's Codes by The Breaking of Japan's Secret Ciphers

Author:The Breaking of Japan's Secret Ciphers
Language: eng
Format: epub
Published: 2015-12-07T16:00:00+00:00

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CENTRAL BUREAU’S BIG BREAK

Despite Fabian’s efforts to have Eric Nave sent ‘home’ to Britain as part of the terms of the Anglo-US Agreement, the Australian code-breaker had been transferred instead to Central Bureau. Fabian was unapologetic over his refusal to share FRUMEL’s signals intelligence with the Royal Navy codebreakers at Kilindini and the US and Australian Army codebreakers at Brisbane. He later recalled:

Security was a paramount concern for me. I was relieved when Commander Nave, an Australian cryptanalyst, left FRUMEL for Central Bureau. He left because I reprimanded him for his lack of security. I also had to get my admiral to remind MacArthur about the need for security. As the commander of the South-west Pacific theatre, MacArthur informed Admiral Leary, who was set up at Brisbane, that he wanted information produced by FRUMEL. Admiral Leary told me that we had to give MacArthur information but asked my suggestion on the best way to supply such material.

I felt that certain restrictions were necessary to ensure security. Admiral Leary issued the following requirements: (1) Fabian or one of his unit’s representatives will report to MacArthur’s headquarters each day at 1400 hours. The FRUMEL representative will never be kept waiting in MacArthur’s outer office. (2) No-one will be authorized to make copies of any material provided by FRUMEL. (3) During the briefing of FRUMEL material, only MacArthur and his chief of staff, General Sutherland, will be present. Everyone else, including General Willoughby, will be excluded from these briefings.

On one occasion Fabian actually burned a signals intelligence document in front of Willoughby to demonstrate that he was not allowed to see it. After the move to Brisbane FRUMEL transmitted a daily radio intelligence summary to the naval staff officer at MacArthur’s headquarters and he conducted the daily briefing. But despite his security concerns, Fabian freely admitted that part of his reason for not co-operating with Central Bureau was that, in his opinion, it had nothing to offer FRUMEL since it was less advanced and had entirely different interests. ‘FRUMEL was concerned solely with information on Japanese naval circuits,’ he said. ‘The Central Bureau was not.’

This was simply not true. Few wars had seen more need for complete co-operation between the army and navy. The Japanese Army was forced by the very nature of the campaigns it was fighting, cut off from its home bases by thousands of miles of ocean, to pass messages on naval communications circuits, often in naval codes and ciphers. Messages would be translated from one system to the other providing a wealth of potential ‘cribs’, if only they could have been followed through the system. There were also a number of joint navy–army codes and ciphers providing potential ‘cribs’.

Naval systems such as JN25, JN40, the merchant-shipping code broken at Kilindini, and JN11, the auxiliary fleet system, all carried large amounts of important military intelligence, particularly on movements of troops. The raw JN25 messages intercepted by FRUMEL’s mainly Royal Australian Navy operators, and by FRUPAC (Fleet Radio Unit Pacific) in

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