Cryptologic Bytes

4 June 1942 - The Battle of Midway "turning point in the Pacific" began. In June 1942, the Japanese had hoped to surprise the American military on Midway Island and claim this crucial location. However, American Navy cryptologists stationed in Hawaii had made some breaks into the Japanese Navy Fleet Code, known to cryptanalysts as JN-25B. Knowing Midway would be attacked, the U.S. Navy and Marines were able to adjust their forces and combat the attack head on. After a series of losses, the United States won a decisive victory over the Japanese Imperial fleet. Damages to the Japanese carrier fleet were insurmountable and their momentum was broken. The Japanese were never able to replace the four aircraft carriers and 332 aircraft.

NCM Curator Patrick Weadon frequently gives talks about the Battle of Midway. In June 2016 he spoke at the 2016 Battle of Midway Ceremony in Annapolis, MD, commemorating the 74th anniversary. Click the link below to learn more and watch a video of his presentation. You can also find a link to a Battle of Midway brochure by Patrick Weadon linked below.

From Wikipedia:

The Battle of Midway was a crucial and decisive naval battle in the Pacific Theatre of World War II. Between 4 and 7 June 1942, only six months after Japan's attack on Pearl Harbor and one month after the Battle of the Coral Sea, the United States Navy under Admirals Chester Nimitz, Frank Jack Fletcher, and Raymond A. Spruance decisively defeated an attacking fleet of the Imperial Japanese Navy under Admirals Isoroku Yamamoto, Chuichi Nagumo, and Nobutake Kondo near Midway Atoll, inflicting devastating damage on the Japanese fleet that proved irreparable. Military historian John Keegan called it "the most stunning and decisive blow in the history of naval warfare." It was Japan's first naval defeat since the Battle of Shimonoseki Straits in 1863.

Many may not be familiar with the story of how Admiral Chester Nimitz knew where to place his ships and planes to prevent a fatal Japanese blow to the U.S. Pacific Fleet.

In the spring of '42, after months of painstaking work to break the Japanese naval code known as JN25, Station Hypo under Commander Joseph Rochefort finally made the breakthrough for which they had been searching. This was not the same "Purple" code the Japanese diplomats used and had been broken months earlier. JN25 consisted of approximately 45,000 five-digit numbers, each representing a word or phrase. More so, the code was modified regularly. Breaking it meant guessing the meanings of enough of these numbers and extrapolating the missing parts so cryptologists could decrypt a whole message.

By May 8, Cmdr. Rochefort knew that a major enemy operation, whose objective was sometimes called AF, was in the offing and could take place somewhere in the Central Pacific. After several sleepless, shower-less, coffee-filled days and nights, he was sure the target was Midway Island. His superiors in Washington needed convincing, however, so he and his team devised a test that would confirm the location of AF. With Admiral Nimitz' permission, Cmdr. Rochefort had the radio station on Midway falsely report that their water distillation plant had broken down, causing a severe water shortage. Within 48 hours, the stations at Hawaii and Melbourne, Australia, decrypted a Japanese radio transmission alerting commanders that AF was short of water.

By May 27, when JN25 was modified again, Cmdr. Rochefort had constructed such a detailed picture of Japanese plans that Cmdr. Edwin Layton, Adm. Nimitz' intelligence officer, was able to predict almost precisely when and where the enemy striking force would arrive with a detailed order-of-battle. With this information, Adm. Nimitz was able to set the trap for what would become the greatest nautical ambush in history.

We remember the cryptologists who accomplished what many thought to be impossible. We also remember the Army and Navy pilots, Marines, and Sailors who fought bravely against all odds and accomplished the greatest nautical victory in the history of naval warfare.

***Visit StationHypo.com (see link below) to follow a 5 part series of blog posts that aired in 2016 -titled, "The Path to Midway."