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

10/04/22 • 56 min

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The Unauthorized History of the Pacific War

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 dif...

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.

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.

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 dif...

Previous Episode

Hit and Run

Sit Rep PTO late December 1941-January 1942

Japanese are on the offensive everywhere
Philippines are already on the way out
Wake Island, despite a gallant defense by the Marines has been captured and the planned relief had been called off December 22.
The fact that Wake Island had been abandoned by Admiral Pye lit a fire under Nimitz to strike back.
Morale was extremely low in the fleet due to the fact that Wake had been abandoned.
Capt McMorris, Pye’s Chief of staff, said that retreating from Wake would be “unduly cautious” and a retreat would “destroy service and public confidence. It is an opportunity unlikely to come again soon. We are in great need of a victory.”
Talk about the effect of Pye’s retreat order on the Carrier Force
Aubrey Fitch withdrew to his cabin so he would not hear the mutinous talk on the bridge.
Fliers on Saratoga threatened to ignore the order and launch anyway.
Intel officer Edwin Layton said, “To lose to an enemy that fought you and you fought well was one thing. But to lose because your own Admiral was a nervous Nellie was another.”
January 1942 was probably the worst month of the war in the Pacific as far as public knowledge and morale went.
Admiral King wants to strike back
In a cable dated January 2, 1942 King told Nimitz that he was not pleased with the “half-hearted” deployment of the CVs.
He desired “Hit and Run” raids in the Marshalls and Gilberts.
Talk about surprise raids to hit the outlying Japanese bases.
Even though King wants to strike back, Nimitz’s advisers say don’t do it
What can Nimitz strike back with?
Talk about the carriers and their availability
CV experience or lack thereof
What are the risks of utilizing the CVs at this juncture?
Who is expressing doubt?
Admiral Bloch 14th Naval District responsible for defending Hawaii
What were the arguments against a raid or raids?
Bloch said that deploying the CVs on raids would leave Hawai’i dangerously exposed to further Jap assaults or invasion
Intelligence on the Marshalls and Gilberts was scarce
Little was known about the targets
Didn’t think it was worth the risk
Why take the risk?
CVs were all we had
Why raid in the first place and why the outer ring?
Morale boost
Japan focused on going south. – this would hit them in their “rear area”
“Turning Movement” not the same as flank attack
Possibly may divert Japanese attention from Australia and the Coral Sea
Hitting the outer ring of islands was easier as there would be less of a threat from heavy Jap fleet units
Would also protect Samoa and Australia by weakening the Jap airfields there
The Marshall and Gilbert Islands Raid
Nimitz confers with Admiral Halsey about the upcoming strike.
Halsey is enthusiastic (no surprise here)
Says that CVs should strike like General Nathan Bedford Forrest said about cavalry, “get to the other fellow first with everything you have and as fast as you can and dump it on him.”
Halsey says he will take Enterprise to the Marshalls himself
What strike isn’t with risk?
Halsey says it’s important for the Navy’s self-respect
Nimitz pulls the trigger
Cryptanalysts state to Nimitz that radio traffic indicated a large Japanese fleet movement south, thereby putting the proposed targets out of range of major enemy fleet units
Set for Feb 1
Will comprise Task Force 8 built around Halsey and CV6 and TF 17 under Fletcher and CV5.
TF8 will strike the Marshalls in the am and if possible strike again that afternoon with targets on Kwajalein, Wotje and Taroa (Moelap)
TF17 will strike the Gilberts area with targets on Mili, Makin and Jaluit
Task Force 8
Due to radio intercepts, Nimitz ordered Halsey to strike deep into the Marshalls at Kwajalein and hit the targets as much and as often as practical.
Halsey told his pilots on CV6 that they would stay all day and “raise a little hell in the Marshalls”.
Pilots were elated
First combat for Halsey & Spruance
Weather was clear, moon was high, no wind, no rain...perfect for flying
Aircrews awakened at 0300
Takeoff at 0445
CV6 launches 37 SBDs and 9 TBDs armed with bombs
VS6 to attack airfield
VB6 to freelance and attack targets of opportunity
As VS6 approached Roi island, Japs scramble fighters, Type 96 Claudes and AAA starts sprouting up as the SBDs go into their glide bombing runs
VS6 CO Halstead Hopping’s SBD is jumped by Claudes and is hit by AAA. He drives directly into the drink.

Next Episode

Scratch One Flattop-The Battle of Coral Sea

While the hit and run carrier raids of February and March tested American carrier doctrine to an extent, and the Pearl Harbor raid as well as Indian Ocean raids tested Imperial Navy doctrine also to an extent, this is the very first time that both navies tested each other’s way of doing things, and in the process found things that worked, and things that well...didn’t work. Let’s dig into it...

Talking Points:

• What sets off the battle of Coral Sea?

o Outline Japanese plans for Operation MO

 Japanese wanted to seize Port Moresby and all of New Guinea. By doing this, it would provide Japan with both a way to isolate Australia as well as New Zealand from allied supply lines, specifically American supply lines.

• Why Rabaul (Opeation R) wasn’t good enough

 This was to be prefaced by the Japanese capture of Tulagi, which is an island we will hear a lot about in the near future. By capturing Tulagi, in the Solomons, the Japanese could patrol the area and the sea lanes to Port Moresby so as to allow their invasion force a free hand.

 As part of the Port Moresby invasion attempt, the invasion group was to be covered by two separate carrier groups, one which centered around the light carrier Shoho, and another which centered around the fleet carriers Shokaku and Zuikaku.

o US intel at Station HYPO and fleet radio unit Melbourne, or FRUMEL decrypt Japanese messages to an extent, and in turn believe that the Japanese will strike the area of Port Moresby, or the northern coast of Australia on or about the first week of May.

 As a result of this intel, Nimitz deploys the only two carrier task forces at his disposal at this time, those centered around USS Lexington, and USS Yorktown, TF 11 and TF 17 respectively, to stand by the area of the Coral Sea with designs to intercept and destroy the incoming Japanese invasion and support fleets.

• On May 1 the two US CV TFs unite under the command of ADM Fletcher

o May 4, Fletcher detaches CV5 to attack recent Japanese positions on Tulagi

 CV5’s attacks are relatively successful, with damage inflicted on enemy positions and shipping in and around the harbor of Tulagi

• US losses are minimal

• By May 6, Fletcher is aware that Japanese CVs are in the area, and the Japanese invasion fleet is not far behind. As a result, he detaches ADM Crace’s cruisers WITHOUT air cover to block the invasion force.

o This is potentially a critical blunder by Fletcher. Crace’s CAs could have been blown out of the water by Japanese CVs, as it was, they were attacked three times by Japanese aircraft and once by MacArthur’s B17s.

 Japanese reports stated that they had sunk a BB, damaged a second BB and a CA. Japanese sent no further attacks towards Crace. His vessels survived due to poor Japanese (and American) accuracy as well as his skillful maneuvering.

 The sighting of the supposed BBs by the Japanese informed the invasion fleet to reverse course

 Still a horrible decision by Fletcher

• First day of the carrier battle May 7

• Early on the morning of the 7th, Japanese launch searches to find US CVs

o Japanese scout planes from Shokaku find US ships and radio ADM Tagaki of 1 CV, 1 CA, and 3 DD.

 What the Japanese actually sight is the detached oiler Neosho and her escort DD Sims.

• How did the Japanese pilot screw this up this bad?

• Japanese arrive over oiler and DD, realize their mistake and continue their search, they return and attack and sink Sims and force Neosho to be abandonned

• At 0815 a CV5 SBD piloted by John Nielsen finds the Japanese screening force under ADM Goto, which includes light carrier Shoho.

o An error in Nielsen’s coding made the message read 2 Japanese CVs instead of 1.

• Fletcher loses his mind on Nielsen when he lands and clarifies his message

 Believing this to be the main Japanese CV force, Fletcher launches everything he has.

• 93 aircraft are flung at Shoho

o 18 F4Fs, 53 SBDs, 22 TBDs from CV2 and CV5

• Lexington Air Group, under Bill Ault arrive over Shoho first

o The SBDs attack first, and score at least 2 bomb hits and the TBDs score 5 torpedo hits

 This is the only real successful TBD attack of WW2

• Lex AG executes a hammer and anvil attack and leave Shoho a wreck

 Talk about Walt Nelson and Ted Wiebe

• Yorktown Air Group arrive next and continue to pummel Shoho.