Station Hypo, with special guest Director of Naval History & Heritage Command Sam Cox

If Seth and I were to define the two main thrusts of our podcast “The Unauthorized History of the Pacific War,” it would be (1) to correct some of the mythology that has emerged over decades, and (2) to see what lessons might be gleaned that could be important were war to break out in the Pacific again. In my view, our subject for today falls into the second category, because it’s about the impact of strategic alignment and chains of command on operational success. Station Hypo was one of three main stations the Navy used to listen to and break Japanese naval codes. Hypo was the phonetic word for the letter “H,” which stood for Hawaii since Station Hypo was the code breaking office located in the basement of the Hawaii Naval District commander’s building in Pearl Harbor. As an aside, I visited those rooms when I was commodore in Pearl, and they were being used to store furniture for the Pearl Harbor shipyard headquarters building, but we will leave that for another potential future discussion on what’s happened to all these historic sites over the decades. But germane to this conversation, in the early months of the war the Naval District Hawaii commander reported, not to Admiral Nimitz, but to Admiral King directly. That would be corrected in the coming months, but since Station Hypo supported combat operations in the Pacific, Admiral Nimitz certainly thought of it as one of his assets, while Admiral King’s staff in Washington saw it as solely and completely theirs, to include Station Hypo’s brilliant leader, Commander Joe Rochefort. This led to a chain of command problem that would ultimately lead to Rochefort’s dismissal as head of Station Hypo, even after his incredible success leading to our victory at Midway. To help us unpack all of this, to include how Station Hypo fed both King’s and Nimitz’s strategic picture, we are proud to host the chief historian of the Navy and Director of Naval History and Heritage Command, retired Rear Admiral Sam Cox. Admiral Cox, welcome. Station HYPO: What was HYPO? Initially known as Fleet Radio Unit Pacific, or FRUPAC Hawaii location for the Navy’s cryptanalysts who monitored radio intel of the Japanese. HYPO was one of two major stations for Allied radio intel, the other being in Melbourne, Australia. Under the command of DC, not Nimitz, or Kimmel for that matter. Conspiracy theory that HYPO never had a PURPLE machine, and therefore was unable to read Japanese traffic pre-Pearl Harbor. NOT TRUE. Purple was the diplomatic code, not the Naval code so HYPO had no reason to have the PURPLE machine in the first place. It would not have helped them in any way. HYPO’s mission after Pearl Harbor, was to decipher the Japanese JN-25 code . Prior to Pearl, HYPO was to decipher flag officer’s code and weather codes Washington worked on JN25 initially How much of the code was readable? Prior to Pearl, they had successfully broken a part of the code, only 10% before the attack. Who was HYPO’s CO and what kind of a man was he? Joseph Rochefort was a Naval enlistee, who never graduated high school. He enlisted in 1918, lied about his age and was later commissioned an Ensign in 1919. Spent several years at sea as well as a year in Tokyo as a language officer. He began work in Cryptanalysis in 1926 Rochefort was assigned as head of HYPO in March 1941 by Intel officer Laurance Safford. Brilliant man who had a knack for solving crossword puzzles and figuring out different types of word puzzles. WAS NOT an eccentric as has been shown in movies. YES, he wore a smoking jacket while at work, only because it had pockets for his pipe and tobacco YES, he wore slippers at work because the concrete floors of the “dungeon” hurt his feet while he paced around trying to figure out messages. HYPO was different than most Naval assignments of the era…how so? Many of the staff of codebreakers were handpicked men by Rochefort Not much in the way of military discipline There was no real system of work, the men were allowed to play their hunches in order to decrypt the information and if that included throwing false messages around to confirm something so be it. There was quite a bit of guesswork involved. Men worked round the clock. Rochefort himself rarely went home, often slept on a cot in his office. Most men worked 12 hour shifts, 7 days a week. How was the JN25 code eventually “broken” what was the process? There were over 50,000 five-digit numeral groups to decipher Codebreakers didn’t necessarily break the code as they actually started to see patterns in the messages and began to plug and play if you will, the different patterns together until something began to take shape. LCDR Thomas Dyer had an uncanny knack for seeing patterns in messages, he said, “if you observe something long enough, you’ll see something peculiar. If you can’t see something peculiar, if ou stare at it long enough, that in itself is peculiar. And then you try to explain the peculiarity.” Traffic analysis Traffic analysis played a large part in the “codebreaking” Reading and noticing a pick up Japanese traffic in certain areas of the Pacific would help determine where and how large of an enemy activity was planned or taking shape. This very trick allowed the Hit and Run Raids on the Marshalls on Feb 1 to take place Cryptanalysts got to where they could tell which Japanese radioman sent which message, and in turn could decipher which ship, or station had sent the message, thereby allowing the intel group to piece together the information that could lead to Rochefort’s team saying whether or not a carrier group was deploying under which admiral and from where. Was the information provided trusted? Initially, no. Admirals like King, specifically King, did not initially trust cryptanalysis. Most of the info they were providing seemed to be guesswork Admiral Nimitz, however, DID trust the intel, and specifically trusted Rochefort and Edwin Layton. This of course, proved very fruitful…