Joseph Rochefort

Joseph John Rochefort (May 12, 1900 – July 20, 1976) was an American naval officer and cryptanalyst.

In 1917, he joined the United States Navy while still in high school in Los Angeles, without obtaining a diploma.

He enlisted in the Navy in 1918, lying that he was born in 1898 so as to appear almost 21 and eligible for the service.

This adjustment lasted his entire career.

He was commissioned as an ensign after a 14 June 1919 graduation from the US Navy's Steam Engineering School at Stevens Institute of Technology, and later in 1919, became engineering officer of the tanker USS Cuyama.

A fellow officer observed that Rochefort had a penchant for solving crossword puzzles and adept skills at playing the advanced card game auction bridge and recommended him for a Navy cryptanalysis class in Washington, D.C.

Rochefort's tours ashore included cryptanalytic training as an assistant to Captain Laurance Safford, and work with the master codebreaker Agnes Meyer Driscoll in 1924.

He was a major figure in the United States Navy's cryptographic and intelligence operations from 1925 to 1946, particularly in the Battle of Midway.

His contributions and those of his team were pivotal to victory in the Pacific War.

Rochefort was born in Dayton, Ohio.

He then served a stint as second chief of the Division of Naval Communications' newly created cryptanalytic organization, OP-20-G, from 1926 to 1929; training in the Japanese language from 1929 to 1932; and a two-year intelligence assignment in the Eleventh Naval District, San Diego, from 1936 to 1938.

Until 1941, Rochefort spent nine years in cryptologic or intelligence-related assignments and fourteen years at sea with the U.S. Fleet in positions of increasing responsibility.

In early 1941, Laurance Safford, again chief of OP-20-G in Washington, sent Rochefort to Hawaii to become officer in charge of Station Hypo ("H" for Hawaii in the Navy's phonetic alphabet at the time) in Pearl Harbor as Rochefort was an expert Japanese linguist and trained cryptanalyst.

Rochefort handpicked many of HYPO's staff, and by the time of Pearl Harbor had gotten many of the Navy's best cryptanalysts, traffic analysts, and linguists, including Joseph Finnegan.

Rochefort's team was assigned to break the Japanese Navy's most secure cypher system, the Flag Officers Code, while Navy cryptographers at Station CAST (Cavite in the Philippines) and OP-20-G in Washington (NEGAT, "N" for Navy Department) concentrated on the main fleet cipher, JN-25.

Rochefort had a close working relationship with Edwin T. Layton, whom he first met on the voyage to Tokyo where both men were sent to learn Japanese at the Navy's request.

In 1941, Layton was the chief intelligence officer for Admiral Husband E. Kimmel, Commander in Chief, Pacific Fleet ( CINCPAC ).

Both he and Rochefort were denied access to decrypts of diplomatic messages sent in Purple, the highest level diplomatic cypher, in the months before the Japanese attack, on the orders of the director of the War Plans Division, Richmond K. Turner.

After the Japanese attack on Pearl Harbor, Navy cryptographers, with assistance from both British cryptographers at the Far East Combined Bureau (in Singapore; later Colombo, Kenya, Colombo), and Dutch cryptographers (in the Dutch East Indies), combined to break enough JN-25 traffic to provide useful intelligence reports and assessments regarding Japanese force disposition and intentions in early 1942.

Rochefort would often go for days without emerging from his bunker, where he and his staff spent 12 hours a day, or even longer, working to decode Japanese radio traffic.

He often wore slippers and a bathrobe with his khaki uniform and sometimes went days without bathing.

Station HYPO maintained the coming Japanese attack would be in the Central Pacific, and convinced Admiral Chester W. Nimitz (who replaced Kimmel).

OP-20-G (with support from Station CAST) insisted it would be elsewhere in the Pacific, probably the Aleutian Islands, possibly Port Moresby in Papua New Guinea, or even the west coast of the United States.

OP-20-G, which had been restructured (Safford having been replaced by Commander John Redman, a communications officer untrained in cryptanalysis) agreed the attack was scheduled for mid-June, not late May or early June, as Rochefort maintained.

Redman also said that Rochefort was being "un-cooperative", and should concentrate on additive recovery.

Admiral Ernest King, Nimitz's superior in Washington, was persuaded by OP-20-G.

Rochefort believed an unknown codegroup, AF, referred to Midway.

One of the Station HYPO staff, Jasper Holmes, had the idea of faking a failure of the water supply on Midway Island.

He suggested using an unencrypted emergency warning in the hope of provoking a Japanese response, thus establishing whether Midway was a target.

Rochefort took the idea to Layton, who put it to Nimitz.

Nimitz approved, and the garrison commander was told by submarine cable to immediately radio in "plain-language" an emergency request for water as an explosion in the water desalination system meant that they had only enough water for two weeks.

An apparently "follow-up" report was to be made in one of the strip-cipher code systems that the Japanese were known to have captured on Wake.

As the plan was to convince Washington, Rochefort tactfully let Fleet Radio Unit, Melbourne (FRUMEL) notify the main objects of the deception (Washington) of the Japanese message by reporting a message from the AF Air Unit saying that they had only enough water for two weeks: "This will confirm identity of AF".

Rochefort then sent a reminder on Friday.

The Japanese took the bait.

Within hours they broadcast instructions to load additional water desalination equipment, confirming Rochefort's analysis.

Layton notes the instructions also "produced an unexpected bonus".

They revealed the assault was to come before mid-June.

In Washington, Admiral Ernest J. King, who disliked Rochefort intensely, still was not convinced, however, as to the date of the attack.

The date-time data in Japanese naval messages was "superenciphered," or encrypted even before it was encoded in JN-25.