The Battle of Midway

"As a result of Cryptanalysts we were able to concentrate our limited forces to meet their naval advance on Midway when we otherwise would have been 3,000 miles out of place." - General George C. Marshall.

Introduction

One of the most significant events that turned the tide of World War II was the Battle of Midway in the Pacific ocean. In the beginning of 1942 the United States was coming off of a treacherous surprise attack by the Japanese at Pearl Harbor, where the U.S. Naval fleet was dealt a near crippling blow. Admiral Chester Nimitz, the U.S. Navy Pacific fleet commander, amazingly enough had all of his carriers and a handful of remaining war ships and submarines left. His counter part, Japan's Admiral Yamamoto, was leading a stubborn campaign with continuous victories in the Pacific ready to deliver the U.S. another blow this time for a big knockout punch. Yamamoto came to the realization that the U.S. had to be defeated immediately before the U.S. could pick up its industrial momentum.

Station Hypo

Around April of 1942, Admiral Chester Nimitz desperately wanted to anticipate Yamamoto's next move. While the ball was in Japan's court at the time, the U.S. Navy had no room for mistakes. The critical moment for the U.S. Navy would lie just ahead, where failure could result in a Japanese invasion of the U.S. West Coast.

One of the means for Admiral Nimitz to gain greater insight of Yamamoto's intentions was to intercept and read Japanese encrypted communication signals. The U.S. Navy radio intelligence group, OP-20-G, established by Laurence Safford in the 1920's, was slowly but surely making progress into breaking Japanese codes. OP-20-G had established a wealth of code breaking officers and enlisted men. The branch of OP-20-G stationed in Hawaii was called Station Hypo.

JN-25

The JN-25 was the Japanese Naval code, that Joseph Rochefort, the head of Station Hypo, and his staff eventually broke with consistency. The JN-25 consisted of roughly 45,000 5-digit numbers, where each number would represent a word or set of words. The Japanese would encrypt their words by using an additive table. So, 2 big steps had to be conducted in order to break and thus read encoded messages, the additive had to be stripped off properly and then pattern analysis of the 5-digit numbers had to successfully take place. One of the down falls for the JN-25 code was that it repeatedly used additive tables. Before the attack on Pearl Harbor roughly only 15% of the Japanese encrypted messages were read by the Allies but because of the attack more serious dedication was made to crack codes.

"AF is Short of Water"

By June of 1942, Station Hypo was able to consistently make conjectures regarding Yamamoto's next moves because of the increased code cracking. Clearly, Station Hypo was getting read outs indicating "AF". Rochefort and Admiral Nimitz's Fleet Intelligence Officer, Ed Layton, felt that "AF" stood for Midway because the Japanese would consistently use "A" for locations in the Hawaiian Islands.

However, in the crucial position that Admiral Nimitz was in, he was skeptical and had to confirm it but how? The commanding officer of the Midway installation sent a message in the clear stating that their fresh water supply was extremely low do to distillation plant damage. So Station Hypo eagerly awaited the inevitable Japanese intercept indication, and sure enough Station Hypo decrypted a Japanese message saying "AF is short of water".

Immediately, thereafter Admiral Nimitz began to plan the ambush against the Japanese armada at Midway. With further cryptanalytic success from Station Hypo, Admiral Nimitz knew that the date of the attack was set for June 3rd, 1942. Because of this date, Admiral Nimitz was able to position U.S. forces appropriately to mount an effective attack. Nimitz positioned his carriers northeast of Midway so they could wait for the Japanese naval forces to arrive. By June 4, the attack had begun and U.S. dive bombers led by Lt. Commander Wayne McClusky from the USS Enterprise, were able to sink 3 out of the 4 Japanese carriers, the Soryu, the Akagi and the Kaga. As the night drew near and the battle continued, U.S. forces then sunk the final Japanese carrier, the Hiyru and came out victorious.

Conclusion

So, the tide began to turn for the Allies in the Pacific against the Empire of Japan. The industrial might of the U.S. began to continuously increase from this point and Japan spent the remainder of the war fighting on its heels. The members of Station Hypo and of the U.S. Armed Forces in the Pacific took the fight to the Japanese and should be honored for their courage and bravery.