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.
Bletchley Park is temporarily closed due to lockdown restrictions
VJ Day 75
1 / 10 — 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.