By breaking a code, they unlocked victory.
Station HYPO, also known as Fleet Radio Unit Pacific, won one of the greatest battles of the war: the battle of intelligence. Naval Intelligence has a long and proud history in the United States' armed forces, and they certainly proved their value during the days leading up to what would become one of the greatest naval victories of all time: the Battle of Midway.
The Battle of Midway is being commemorated this year for its 70th anniversary. The battle, which took place from June 4-8 1942, was a turning point in the Pacific War and arguably set the stage for the United States to help win the Second World War. A ceremony will be taking place at the Navy Memorial located on Pennsylvania Avenue NW between 7th Street Northwest and 9th Street Northwest in downtown Washington on June 4.
The battle is noted as being the first real turning point in the war, and the first decisive victory by the United States in the war with Japan. The Imperial Japanese Navy (IJN) had already made broad strokes in the Pacific, beginning with the attack on Pearl Harbor, the invasion of the Philippines, Malaya and Singapore, the Battle of Wake Island and recently a tactical victory at Coral Sea.
With these victories, however, came a sort of overconfidence of the Imperial Fleet, and they first started to show weakness with the breaking of JN-25, the naval cryptography used by the Japanese navy in 1942. Although it wasn't the first Japanese code to be broken by U.S. forces, nor the last, it was supremely important.
JN-25, as it was called by American intelligence officers, was used for high-importance transmissions, such as ship movement and other commands. Preceding the attack on Pearl Harbor, JN-25 was sparsely used due to the lack of any large operations in the Pacific, which gave American cryptanalysts little to work with. Although the United States had cracked the PURPLE code, used by the Japanese Foreign Office, ultra-nationalists in the armed forces did not trust the diplomatic service and did not transmit much for the U.S. to work with.
JN-25 also had a tendency to change, and almost every adjustment lead to a new start for intelligence teams at HYPO. Also, leading up to Midway with sister intelligence stations being threatened by Japanese advance, HYPO was placed under extreme pressure to crack the code. Lt. Cmdr. Joseph Rochefort, the head of the HYPO station, pushed his team for 36-hour shifts, and has been reported to have worked in his bathrobe and shown up to briefings and meetings disheveled.
"By the middle of March 1942, two viable naval radio intelligence centers existed in the Pacific: one in Melbourne, Australia [FRUMEL], and one, HYPO, in Pearl Harbor, Hawaii... The center on Corregidor was no longer affiliated with a fleet command, and its collection and processing capabilities were rapidly disintegrating as a result of evacuations of personnel to Australia and destruction of its facilities by bombing and gunfire," said National Security Agency historian Frank Parker.
But despite (or perhaps because of) this extreme pressure, HYPO and the command station in Washington D.C. delivered in fine fashion. By late May 1942, the teams had cracked enough of the code to understand the gambit being developed to flush American ships out of the protection of Pearl Harbor, and by doing so allowed Adm. Chester Nimitz to set a trap of his own. Although credit is due to Nimitz for taking a gamble and winning, because of the work at HYPO and the rest of Naval Intelligence, it was an educated gamble that led to the United States winning the war.
“It was miraculous; our intelligence predicted the time of the planned attack, the distance and location of the Japanese,” said Capt. John Crawford, a Midway veteran. "Our intelligence had solved the problem. I was happy as a clam."