Thread by @TrentTelenko

The subject of this thread is the IJNAS C3I system behind the destruction of Force Z.

(I'll be using clips from Angus Konstam's book to illustrate this thread)
ospreypublishing.com/store/military…
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The anniversary of the sinking of Force Z is on the minds of many #twitterhistorians

For example, @ArmouredCarrier has three really nice videos on YouTube about the sinking of HMS Repulse
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Konstam's book is wonderful for most of the journalistic "Who, What, Where, When, How, & Why" on Dec 10, 1941, but it leaves out how the command control, communications & intelligence worked for the IJNAS Rikko Kokutai and why it came into existence in time to destroy Force Z.
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This is _NOT_ a knock of Konstam's book. Osprey books are extremely focused in format & there isn't space for more.

The glossing over of the IJNAS C3I has a price, missing that PoW & Repulse were as much the victims of Adm Isoroku Yamamoto as the USN battleline at Pearl
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Harbor.

In WW2, the Imperial Japanese were a fell high technology power punching in terms of naval & air power with the USA & UK until combat attrition exhausted the Japanese of the skilled air crew in 1943 without adequate replacements.
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The Yamato class battleships, the Zero fighter, Betty torpedo bomber and Type 93 "Long Lance" torpedoes were all examples of cutting edge Japanese military innovation before Pearl Harbor.

The man who guided IJNAS technological development as Japan transitioned from a
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challenging military power - that is a military which copied to keep up - to an innovating military power that built it's military technology to fit its own warfighting concepts and doctrines was Adm Isaroku Yamamoto.

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The time of Yamamoto's planning that led to the execution of Repulse & the Prince of Wales dates from the 1929 - 1934 period when he was chief of the Technological Division of the Naval Air Corps and participated in the London Naval Treaty delegation.
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pacificwrecks.com/people/veteran…

In that period Yamamoto had a role in getting night flight pay instituted for naval flyers in 1932 plus both adopted and deployed a Japanese Empire wide radio direction finding navigation system with grid square maps. The Grid Square map
(Western Approaches grid in photo)
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was so fleet scout planes operating near Japanese possessions or land based direction finding array could quickly give quick coded reports as to where enemy fleets and commerce raiders were, especially at night with aerial scout radio direction finding gear.

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USN wartime intelligence stated that the "Model 2 Aircraft (Hi) Mk 1 Direction Finder" found on the G3M Nell & G4M Betty bombers was a copy of a Telefunken RDF system (closest match at link).

No mention was made of the associated M/F homing beacons.

cryptomuseum.com/df/telefunken/…
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This "Yamamoto C3I system" of grid maps & medium freq. (M/F) beacons were in wide spread service in 1937 and perhaps being tested as early as 1932.

They were the target marking sword of the IJNAS Rikko Kokutai compared to the Dowding System's shield for Fighter Command.
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The failure of Western intelligence, & particularly by UK Royal Navy to catch this Yamamoto System during IJNAS air operations over China 1937-1941 lead to the loss of Force Z.

Radio Beacon ops were central to Rikko Kokutai radio procedures (Chart 79) bombing of Chongqing
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The USN also shares blame here, but to a lessor extend than the RN by reason of American civil aviation politics & tech

1930's era US civil aviation did not use light house style non-directional beacons Europe & Japan did. Radio range beacons created beams that airlines flew
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...like aviation railroads.

There was simply no such excuse for British Naval Intelligence in 1941, given that Luftwaffe used non-directional beacons that were jammed by the RAF in 1940 during the Battle of the Beams.
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Returning to this Yamamoto radio beacon/grid map system, it allowed for multi-airfield, time on target, air strikes with massed torpedo bombers.

Especially at night, when the medium frequency/AM radio band had a much longer range.
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For Force Z, it was the Yamamoto C3I System's ability to rapidly mass widely dispersed Rikko Kokutai to arrive at the same grid coordinates over the ocean _simultaneously_ that doomed it.
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Too many well coordinated Japanese torpedoes and bombs from too many directions at once overloaded PoW & Repulse's anti-aircraft defenses and made jinxing to avoid them futile.
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The Yamamoto C3I system was pulled apart and analyzed by US are very well documented in the following:

SRH-289 THE EMPLOYMENT OF MOBILE RADIO INTELLIGENCE UNIT BY COMMANDS AFLOAT DURING WWII

SRH-309 PACIFIC OCEAN MOBILE RADIO INTELLIGENCE UNIT REPORTS 1945 Parts 1, 2 & 3
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All told, these Ultra histories recorded 854 times that USN mobile "Radio Intelligence Units" (RIU) AKA the 'On The Roof Gang' intercepted the IJNAS aerial scouts calling out grid locations in their scouting of the USN carrier battle groups 1943-1945. 20/

The USN captured the master grid reference map for the entire Japanese Empire when IJN Fleet headquarters in the Marianas was overrun.

The first operations where RIU's made use of this captured IJN geographic grid map started in Dec 1944 when Adm Halsey took TF 38 from
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Ulithi into the Great South China Sea raid in early January 1945.

When you read the War Diaries of that raid. You find that Halsey was using the cover of a typhoon to move through the South China Sea to avoid IJNAS aerial scouts.
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British Naval Intelligence was fully appraised of the grid maps used by the Yamamoto C3I System in 1945 when RN signals officers from the British Pacific Fleet were posted with RIU Task Force 58.

The names of those RN officers were deleted from Ultra histories clipped below.
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As far as I've been able to determine. There has been no reference to this IJNAS radio beacon/grid map system outside USN Ultra histories.

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P.S.

How the Yamamoto C3I System effected the Guadalcanal Campaign -- it's where the slides for this tweet thread came from -- was premiered on @ww2tv YouTube channel

The Horseshoe Nail of Victory of the Guadalcanal Air Campaign

@threadreaderapp unroll please.