Code breaking that changed World War II 

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“Military Intelligence is the key to war, without it, you cannot win.” -- Sun Tzu 

After the successful “Doolittle Raid” on mainland Japan in response to Pearl Harbor, the Japanese knew they needed to expand their control throughout the Pacific. In south Asia they conquered nations at an impressive pace, capturing Hong Kong, Singapore, and the Philippines. 

In May of '42, the Allies and Japanese fought their first major naval engagement of the war, the Battle of the Coral Sea. It was the first time ships did not meet in combat, but rather aircraft from carriers clashed, inflicting mutual devastation. The action did slow the Japanese expansion efforts in southern Asia, but where would their main push be to expand their control over the mid-Pacific? 

CODE BREAKERS 

In a small windowless bunker at Pearl Harbor, Lt. Commander Joseph Rochefort and his team of cryptanalysts made up the U.S. Navy’s Combat Intelligence Unit known as Station Hypo. They were good, real good, having cracked the Japanese Naval code little by little and now could decipher most enemy transmissions. 

In April of '42, they developed a process where they could intercept, decrypt and translate most Japanese high command orders in hours. 

Rochefort thought he knew where the major Japanese assault was coming, Midway Island. The U.S. had just completed construction of an air base and port facilities on this tiny strip of land strategically half way between the U.S. and Japan, approximately 1,200 miles northwest of Hawaii. 

Problem was, not everyone who Rocheport reported to in Washington believed the codebreakers were right. It was clear that a new offensive was coming, but where? The messages kept referring to “AF” as the target. 

This would be another brazen attack by Admiral Isoroku Yamamoto, the mastermind behind Pearl Harbor. Yamamoto had spent time in the United States, knew our potential industrial capability and wanted to make another aggressive move before the U.S. fully unleashed its industrial might.

Rochefort had received transmissions from Japanese spotter planes talking about weather conditions, tides and terrain on “AF.” All describing Midway “to a T.” 

Deception was the name of the game, Rocheport and his team devised a ruse to prove “AF” was Midway Island. Through submarine communications, he had the commander on Midway radio that the saltwater evaporator on the island had broken and they were running out of fresh water. It worked, two days later they intercepted a message stating “AF” was running out of drinking water. 

Still Washington was leery. 

Rocheport needed to do something drastic, they had learned more on the now impending attack just weeks away. He had served with the overall commander of the U.S. Pacific Fleet Admiral Chester Nimitz’s intelligence officer Lt. Commander Edwin Lawton, in of all places Japan for three years. They were friends. Breaking protocol and risking disciplinary action, Rocheport contacted Lawton directly, convincing him of his team's discovery. 

Yamamoto’s plans were in motion. 

On June 3, as a feint, the Japanese attacked the Aleutian Islands off of Alaska, wanting the U.S. to react with a strong naval response out of Pearl Harbor. Nimitz however had a small contingent already close, but knew through Station Hypo’s work this was a ploy to draw the Navy’s attention away from Midway. 

Yamamoto planned a three-prong attack.

To the Northwest, four carriers with a slew of support ships and 100-plus planes will initially bomb the tiny Island, destroying defenses. Of those carriers, Akagi, Kaga, Soryu and Hiryu had all taken part in the Pearl Harbor attack six months earlier, Grrrr! 

Coming from the Southeast would be heavy cruisers and destroyers carrying 5,000 invaders who will storm the beaches, eliminating whatever resistance was left and occupy the island. 

Six hundred miles away in his command task force was Yamamoto himself, directing the well designed, he thought, surprise attack. 

Once the depleted U.S. response came from Pearl to Midway, the four carriers plus Yamamoto’s fleet of battleships and heavy cruisers would attack those ships in a Naval battle that would decide who controls the Pacific. 

Pearl was abuzz. After the early Battle of the Coral Sea in which the aircraft carrier Lexington was sunk and Yorktown crippled, the Navy had only two carriers in the theater left, but … as the Yorktown limped back to Hawaii and into dry dock, it was estimated rushed repairs would take two weeks, the Navy got it done in 48 hours. She would join Nimitz’s task force.

Using Rocheport’s information, Nimitz prepared his own surprise for the Japanese. Risking much, not holding a carrier in reserve, the U.S. Navy deployed two task forces for the ambush. 

Yamamoto was about to receive the shock of his life! 

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Bob Ford’s History will appear in each edition of the Midweek and Weekender. You can find more of Bob’s work on his website bobfordshistory.com and videos on YouTube, TikTok and Clapper.