Who was Joseph Rochefort and What Did He Do?

At the epicentre of the US Navy’s code-breaking efforts for over twenty years, Captain Joseph John Rochefort was the cryptanalyst who cracked the Midway Code. What follows is his story.

19 December 2022

Joseph Rochefort, cryptanalyst, linguist, and Navy captain was at the epicentre of the US code-breaking efforts for over twenty years. As head of World War II code-breaking unit, Station HYPO in Hawaii, he was instrumental in the pivotal US victory at the Battle of Midway.

So who was Joseph John Rochefort, the man who cracked the Midway Code? Read on as we decipher his story.

Early Naval Career

A pair of spectacles with a crossword puzzle (Photo: Jennifer A Smith via Getty Images)

Joseph John Rochefort was born in Dayton, Ohio in 1900. However, when he enlisted in the US Navy just short of his 18th birthday, he stated his birth year as 1899, later adjusting it to 1898 to be eligible for the Navy’s Steam Engineering School. This latter date would remain uncorrected for his entire military career.

After graduating, Rochefort spent five years aboard the oil tanker the USS Cuyama. He served in several positions including engineering officer. During this time, his commanding officer noted Rochefort’s talent at solving riddles, puzzles and crosswords. He was so impressed, he recommended him for a transfer to intelligence.

Joseph Rochefort wed Elma Fay Aery on 16 May 1921. They were married for 48 years. She died in 1969.

Joseph Rochefort: Cryptanalyst in Training

Joseph Rochefort (Photo: Bettmann / Contributor via Getty Images)

In 1925 Rochefort was assigned to the Navy’s newly created cryptanalytic force, known as the Code and Signal Section, OP-20-G. There, he trained under the cryptological department’s creator, Laurance Safford, as well as the so-called ‘first lady of naval cryptology’ Agnes Meyer Driscoll. He rose up in the ranks, becoming Safford’s second in command, a position he held for about four years.

From 1929 to 1932 Captain Rochefort served as an attaché in Japan, immersing himself in the culture and learning the language. And it was in Tokyo that he met Lieutenant Commander Edwin T. Layton. Their friendly association would play an important role in the course of history.

Appointment As Head of Station HYPO

Alan Turing, instrumental in breaking Germany's 'enigma' code (Photo: Pictures from History via Getty Images)

In 1941, Safford appointed the then Lieutenant Commander Joseph Rochefort as head of the US Navy’s signals monitoring and cryptographic intelligence base. Located at Pearl Harbor in Hawaii, this was better known as Station HYPO.

Within the year, Joseph Rochefort and his team of codebreakers, linguists and radio traffic analysts, with help from UK analysts Alan Turing and John Tiltman, made a breakthrough. They cracked JN-25, the Imperial Japanese Navy’s most secure command and control communications code. By April 1942, Rochefort and his team were decrypting and analysing Japanese messages within hours of being sent, at a rate of around 140-a-day. This proficiency was about to prove invaluable.

The Man Who Cracked the Midway Code

Admiral Chester W. Nimitz, Commander in chief of the Pacific Fleet (Photo: Bettmann / Contributor vis Getty Images)

In May 1942, Rochefort’s team discovered that the Japanese were planning a major attack somewhere in the Pacific theatre. They intercepted messages indicating that Admiral Isoroku Yamamoto, architect of the attack on Pearl Harbour, was planning something on an even more catastrophic scale at a location codenamed AF.

But where was AF? Rochefort’s team were adamant it referred to the US air base on Midway Atoll in the central Pacific Ocean. However Rochefort’s superiors believed the attack would be elsewhere, in the South Pacific. Washington had even specifically discounted Midway as a target.

At odds with Navy Intelligence, Station HYPO conducted a test to prove their case. They sent a fake message relating to Midway for the Japanese to intercept. This proved successful when the Japanese later corresponded about that message, referring to Midway as AF.

Rather than following the normal chain of command, Rochefort approached his long-time friend from his time in Japan, Edwin T. Layton. Layton, now a Lieutenant Commander, was the intelligence officer to Admiral Chester W. Nimitz, commander in chief of the US Pacific Fleet at Pearl Harbor. In what would prove a fateful move, Nimitz agreed with Rochefort’s assessment and planned accordingly.

The net result was a stunning victory for the US at the Battle of Midway; an event that all but ended Japan’s efforts to control the Pacific. And by all accounts, Joe Rochefort’s Midway Code discovery was instrumental in this success. Many argue this was a turning point in the war, but rather than elevate his career, the incident would all but end it.

What happened to Joseph Rochefort?

The Battle of Midway (Photo: Pictures from History via Getty Images)

Soon after the Battle of Midway, Joseph Rochefort was relieved of his cryptanalysis and intelligence gathering detail and reassigned to command a floating dry dock in San Francisco. This has long been interpreted by some as an act of vengeance by those superiors whose authority he circumvented.

Rochefort never served at sea again. After becoming head of the Navy’s Pacific Strategic Intelligence Section in 1944, he retired at the rank of captain in 1953. Captain Rochefort died at the age of 76 in the city of Torrance, California on 20 July 1976.

Joseph Rochefort’s Legacy

Memorial to WWII veterans, and the loss of life at Pearl Harbor (Photo: JPecha via Getty Images)

Joseph Rochefort once said, ‘We can accomplish anything provided no-one cares who gets the credit’. However his achievements have not gone unnoticed. He was posthumously awarded the Navy Distinguished Service Medal, the Presidential Medal of Freedom and the National Defence Service Medal. In January 2012 the Capt. Joseph J. Rochefort Building was dedicated at the National Security Agency facility in Pearl Harbor.


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