Joe Rochefort: The Man Who Turned the Pacific Theater of WWII

by Martha Hutchens

image by @everett225, deposit photos

He was an unlikely sort to be able to make such a claim. While he was a naval officer, he was by all accounts an indifferent seaman. He was known to wear slippers and a smoking jacket to his most important WWII assignment. His work was not even acknowledged until years after his death. He was politically inept and narrowly escaped a court-martial in 1921, when the tanker he was duty officer on dragged its anchor in San Francisco Bay.

And yet, all of the war in the Pacific turned on this single man.

To understand this, you have to understand the Battle of Midway, fought on June 4–7, 1942. At this point, much of the U.S. Pacific Fleet was still on the ocean floor at Pearl Harbor. The U.S. had at best three functional carriers, but two was more accurate. Japan had ten operating carriers. The Battle of Coral Sea was fought in May 1942 and stopped Japan’s advance but was technically a draw. The Battle of Midway was the first clear U.S. victory in the Pacific and ended with the sinking of all four Japanese carriers there. Most historians consider it the turning point of the war in the Pacific.

So what was Rochefort’s assignment? He led Station HYPO, the Navy’s codebreaking unit.

Rochefort first started work in cryptanalysis in 1925. Codebreaking was not a prestigious assignment. Everyone knew you had to go to sea to get promoted. But it appealed to Rochefort. In 1929, he was posted to Japan for three years, where he was to learn the language. He then spent several years at sea until returning to Pearl Harbor in late 1939.

In late 1940, the U.S. Army broke the Japanese code Purple. This was a diplomatic code, not a military one. The equivalent Navy code was designated JN-25, and it became Station HYPO’s main objective.

image by @zim90, deposit photos

In December 1941, JN-25 remained unbroken. Traffic analysis told the team that the Japanese were planning something big, but the target was elusive. For months, Rochefort had been tracking large units of the Japanese fleet, but in mid-November Admiral Yamamoto put up a dense “electronic smokescreen” that allowed the carriers that attacked Pearl Harbor to slip through. The team at Station HYPO was devastated at their intelligence failure, which in reality belonged equally to the Army, the Navy, and Washington politicians.

Not long after Pearl Harbor, Rochefort told his team to “Forget Pearl Harbor and get on with the war.”

When Admiral Nimitz was assigned to be the Pacific Commander-in-Chief, he was not impressed with Rochefort, who narrowly kept his position.

Rochefort was not responsible for the actual codebreaking—that task fell to Lieutenant Commander Thomas Dyer, who led the work beautifully. By mid-January 1942, HYPO was decrypting fragments of messages. By the end of March, Americans were reading a substantial number of JN-25 messages.

Rochefort’s responsibility was to determine the significance of these messages, a difficult task considering well more than half of the messages they received remained unbroken. And in early 1942, his record was spotty. He did accurately predict an air raid on Hawaii on March 4, 1942. Buried in the minutiae of these decryptions was the Japanese designation for Midway: AF.

In early May, HYPO was receiving between 500 and 1,000 intercepts per day and reading parts of around 60% of them. Rochefort told Nimitz it was clear the Japanese were planning a major new initiative, but he didn’t know where.

Many potential targets were considered—Pearl Harbor, the U.S. West Coast, even the Aleutian Islands (where there was a small incursion, but that’s a different blog post).

image by @PhotoWorks, deposit photos

But on May 13, a decryption landed on Rochefort’s desk. A Japanese ship was to load supplies and proceed to Affirm Fox—AF. With tens of thousands of messages between the two of interest, Rochefort remembered that AF was Midway. Nimitz sent Captain Lynde McCormick to “the dungeon," the home of Station HYPO. It took a full day, but Rochefort and crew convinced him that Japan intended to commit four carriers to Midway. Then they had to convince Washington, and no one there had much confidence in Rochefort.

But Nimitz did, and this was confirmed by another intercept on May 16. But how to convince Washington?

Here comes one of the most impressive sleights of hand in military history. One of Rochefort’s subordinates, Jasper Holmes, suggested sending an encrypted message to the naval air station on Midway. It instructed the officers there to send an unencrypted message reporting difficulties with their distillation plant.

Midway had no source of fresh water and depended entirely on these plants. Not long after, HYPO decrypted a message saying there was a water problem on AF. The ruse had worked.

The battle at Midway was hard fought, and the victory required both skill and a measure of luck. But America’s fleet wouldn’t have even been there if it weren’t for Joe Rochefort.

He was nominated for a Distinguished Service Medal, but the recommendation was quashed. In Washington, Rochefort was considered an insubordinate cuss, difficult to work with and unpleasant to be around. He was relieved of duty at Station HYPO in October 1942.

Joe Rochefort died in 1976. In 1985, he was awarded the Distinguished Service Medal posthumously. And even today, few know his name or the pivotal role he played in WWII.

Best-selling author Martha Hutchens is a history nerd who loves nothing more than finding a new place and time to explore. She won the 2019 Golden Heart for Romance with Religious and Spiritual Elements. A former analytical chemist and retired homeschool mom, Martha occasionally finds time for knitting when writing projects allow.

Martha’s debut novel, A Steadfast Heart, is now available. You can learn more about her books and historical research at MarthaHutchens.com.

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