Hut 7


Hut 7 was a wartime section of the Government Code and Cypher School at Bletchley Park tasked with the solution of Japanese naval codes such as JN4, JN11, JN40, and JN-25. The hut was headed by Hugh Foss who reported to Frank Birch, the head of Bletchley's Naval section.
Hut 7 supplied cryptanalysts and linguists to Bletchley's front line station the Far East Combined Bureau at Hong Kong, then Singapore, then Anderson Station, then Allidina School in Kilindini, Kenya before moving back to Colombo.
Bletchley co-operated with the US Navy Code and Signals Section known as OP-20-G in Washington D.C., and with FRUMEL in Melbourne ;
see Central Bureau and FRUMEL.

Pre-War origins

Among the first challenges was overcoming the special kana and romaji Morse code system used by the Japanese. GC&CS began breaking Japanese diplomatic traffic in the early 1920s. GC&CS subsequently attacked the Naval Reporting Code, and General Operations Code.
The section was headed by William "Nobby" Clarke with Harry Shaw and Ernest Hobart-Hampden. These were later joined by Eric Nave, seconded from the Royal Australian Navy, John Tiltman, and Hugh Foss.
GC&CS operated the Far East Combined Bureau, the codebreaking and intercept station in Hong Kong prewar, which during the war moved to Singapore, Colombo and Kilindini.

WWII expansion

Potential linguists and cryptographers were recruited from the University of Cambridge and the University of Oxford by referral through people like the Revd Martin Charlesworth, A.D. Lindsay, Dr C. P. Snow, and Theodore Chaundy. Candidates were interviewed and approved by a board that included Colonel Tiltman. Successful candidates received a final interview at Bletchley by a senior representative of their section.
At the outset of World War II, Britain had few Japanese linguists and conventional wisdom held that it would require two years to produce qualified linguists for the war effort. In February 1942, an accelerated program was established to train linguists to assist with Japanese signals intelligence. Candidates were put through an intensive six-month course taught by Captain Oswald Tuck, RN. The course was taught in various locations in Bedford including the Gas Company. The course produced linguists for the Navy, Army, Air Force, and Foreign Office. Some of the linguists were sent on to Bletchley, while others were sent to London to work with Captain Malcolm Kennedy.
Later cryptanalysts did not require linguistic training, so could be recruited and put to work directly. Some of these cryptanalysts received a shorter version of the Japanese language course.
The Japanese Naval Section was originally stationed at the Elmer School near Bletchley. By August 1942, the unit consisted of 40 people. The unit was moved inside Bletchley Park in September and again in February 1943 to Hut 7. The unit expanded later to Block B.
The wooden structure of the hut was demolished sometime between 1948 and 1954.

Contributions

In addition to code books and manual ciphers, the Imperial Japanese Navy also utilized electric cipher machines known as JADE and CORAL using the same technology as PURPLE. While OP-20-G took the lead on these systems, Bletchley provided some contributions.
In 1921, GC&CS was able to provide insight into the Japanese bargaining position at the Washington Naval Conference of the nine major powers and limit their ambitions.
Pre-war accomplishments were helped tremendously by the death of Emperor Taishō in 1926. The repetition of the formal announcement provided GC&CS with cribs into almost every code in use. Later in 1934, Foss was able to break an early Japanese cipher machine.
Tiltman provided the major break into JN25 in 1939.
In early 1942, decrypts from Anderson gave advance warning of Vice Admiral Nagumo's Indian Ocean raid including a planned attack on Colombo. The warning allowed the British to limit damage, improve opposition, and evacuate the fleet and the cryptanalysts from Colombo to Kilindini.
In May 1945, the team at HMS Anderson successfully broke a message in JN25 that provided details of a supply convoy going from Singapore to the Andaman Islands. This message provided details that led to the sinking of the Japanese cruiser Haguro in the Battle of the Malacca Strait.

List of Hut 7 personnel

The following people served in Hut 7, HMS Anderson, and Kilindini: