by Gerald Boerner
"I couldn’t help but overhear, probably because I was eavesdropping"
— Anonomous
"the vast majority of security failures occur at the level of implementation detail"
– Ross Anderson, 1993.
“It’s an engrossing look at the way the flow of information shapes history–as well as a rare glimpse into the soul of the hardcore geek”
— Lev Grossman
"As soon as men decide that all means are permitted to fight an evil, then their good becomes indistinguishable from the evil that they set out to destroy."
— Christopher Dawson, The Judgment of Nations, 1942
“Cryptography is like literacy in the Dark Ages. Infini tely potent, for good and ill… yet basically an intellectual construct, an idea, which by its nature will resist efforts to restrict it to bureaucrats and others who deem only themselves worthy of such Privilege.”
— Vin McLellan, in “A Thinking Man’s Creed for Crypto”
Pearl Harbor: The U.S. Reads Japanese Communication Codes
The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well. Every Japanese code was eventually broken, and the intelligence gathered made possible such operations as the victorious ambush at Midway and the shooting down of Isoroku Yamamoto in Operation Vengeance.
The Imperial Japanese Navy (IJN) used many codes and ciphers. All of these cryptosystems were known differently by different organizations; the names listed below are those given by Western cryptanalytic operations.
Japanese Codes before World War II
The Japanese did not place so much emphasis on codes & cipher systems as their language was totally different to most European languages & so thought to be unlearnable .
Japanese is usually written as a mixture of Chinese characters Kanji & 2 alphabets hiragana & katakana. It is written in Chinese pollysyllabic characters written from the top right hand corner going down in columns progressing to the left.
In World War Two Japan made extensive use of code books. The Japanese Naval code book known to the Allies as JN25 started before the war but was enhanced during the war. First broken in the late 30′s by U.S.& U.K. it used a system of digits from an additive key book. This was added to a group of digits obtained from looking up a word or phrase to be encoded. The resultant addition added was transmitted. The recipient looked up the additive table and subtracted the additive group to arrive at a word or phrase. Codebreakers had to recreate the additive table as well as the code book.
Red code… This was a code book system used in World War I and after. It was so called because the American copies made of it were bound in red covers. It should not be confused with the RED cipher used by the diplomatic corps.
This code consisted of two books. The first contained the code itself; the second contained an additive cipher which was applied to the codes before transmission, with the starting point for the latter being embedded in the transmitted message. A copy of the code book was obtained in a "black bag" operation on the luggage of a Japanese naval attache in 1923; after three years of work Agnes Driscoll was able to break the additive portion of the code.
Blue code… This was another code book system which succeeded the Red code.
In order to prevail, Nimitz had to have some sense of Japan’s intentions. The task of obtaining the critical information required to turn the tide in the Pacific fell to OP-20–G, the Navy radio intelligence organization tasked with providing communications intelligence on the Japanese Navy. Established in the early 1920s by Laurence F. Safford, the " Father of Navy Cryptology," OP-20 –G was key to Nimitz’s planning. In addition to his earlier cryptologic efforts, Safford had played a major role in placing Commander Joseph Rochefort in command of Station Hypo, the Navy’s codebreaking organization at Pearl Harbor. Over a period of 18 years, OP-20-G had developed a highly skilled group of officers and enlisted men.
Station HYPO, Hawaii
Station HYPO, also known as Fleet Radio Unit Pacific (FRUPAC) was the United States Navy signals monitoring and cryptographic intelligence unit in Hawaii during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units in the Pacific theaters, along with FRUMEL in Melbourne, Australia. The station took its initial name from the phonetic code at the time for "H", as in "Hawaii". The precise importance and role of HYPO has been the subject of considerable controversy, reflecting internal tensions amongst US Navy cryptographic stations.
HYPO was under the control of the OP-20-G Naval Intelligence section in Washington. It was located, prior to the attack on Pearl Harbor of December 7, 1941, and for sometime afterwards, in the basement of the Old Administration Building at Pearl Harbor. Later on, a new building was constructed for the station, though it had been reorganized and renamed by then.
For an interview of a U.S. Navy codebreaker assigned
to the Station HYPO in Hawaii, Click HERE…
Cryptanalytic problems facing the United States in the Pacific prior to World War II were largely those related to Japan. An early decision by OP-20-G in Washington divided responsibilities for them among CAST at Cavite and then Corregidor, in the Philippines, HYPO in Hawaii, and OP-20-G itself in Washington. Other Navy crypto stations, including Guam, Puget Sound, Bainbridge Island were tasked and staffed for signals interception and traffic analysis.
The US Army’s SIS broke into the highest level Japanese diplomatic cypher (called PURPLE by the US) well before the attack on Pearl Harbor. PURPLE produced little of military value, as the Japanese Foreign Ministry was thought by the ultra-nationalists to be unreliable. Furthermore, decrypts from PURPLE, eventually called MAGIC, were poorly distributed and used in Washington. SIS was able to build several PURPLE machine equivalents. One was sent to CAST, but as HYPO‘s assigned responsibility did not include PURPLE traffic, no PURPLE machine was ever sent there. The absence of such a machine on site in Hawaii has long been seen by conspiracy theorists as a reason for US unpreparedness in Hawaii, and/or to be evidence of a conspiracy by high level officials to deprive Pearl Harbor of intelligence known to Washington. However, no uncontroverted hard evidence for any such conspiracy exists.
Japanese naval signals in 1941 & early 1942
HYPO was assigned responsibility for work on Japanese Navy systems, and after an agreement with Australia, the United Kingdom and Netherlands to share the effort, worked with crypto groups based at Melbourne, Hong Kong and Batavia. Prior to the attack on Pearl Harbor, the amount of available IJN traffic was low, and little progress had been made on the most important Japanese Navy system, called JN-25 by U.S. analysts. JN-25 was used by th IJN for high level operations: movement and planning commands, for instance. It was a superencrypted code, eventually a two-book system, and was about the state-of-the-art at the time. Cryptanalytic progress was slow. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 Dec 41, at which time a new edition of the system went into effect sending the cryptanalysts back to the beginning.
LCDR Joseph J. Rochefort led
and handpicked many of the
key codebreakers at HYPO.
After the attack on Pearl Harbor, there was considerably more JN-25 traffic as the Japanese Navy operational tempo increased and geographically expanded, which helped progress against it. Hong Kong’s contribution stopped until the crypto station there could be relocated (to Ceylon and eventually Kenya), but HYPO and the Dutch at Batavia, in conjunction with CAST and OP-20-G made steady progress. HYPO in particular made significant contributions. Its people, including its commander, Joseph Rochefort, thought a forthcoming Japanese attack early in 1942 was intended for the central Pacific, while opinion at OP-20-G, backed by CAST, favored the North Pacific, perhaps in the Aleutians.
In early 1942, in response to the Japanese advances in the Philippines (which threatened CAST), the possibility of an invasion of Hawaii, and the increasing demand for intelligence, another signals intelligence center, known as NEGAT was formed in Washington, using elements of OP-20-G. In the words of NSA historian Frederick D. Parker:
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 (CAST) 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.
One of HYPO‘s personnel was responsible for the ruse which identified a call sign used in the Japanese traffic related to new offensive operation being planned. This involved a false claim of a fresh water shortage on Midway, broadcast in clear, which succeeded in evoking an encrypted Japanese response, noting that AF was reporting water troubles. Since AF was the apparent focus of the upcoming operation, it was clear that Midway would be the primary target.
As mid-1942 approached, HYPO was under high pressure, and there are tales of 36-hour stints, of Rochefort working in his bathrobe and appearing for briefings late and disheveled besides. This effort climaxed in the last week of May with the decryption of enough JN-25 traffic to understand the Japanese attack plan at Midway in some, but not complete, detail. This allowed Admiral Nimitz to gamble on the ambush which resulted in the Battle of Midway, the loss of four Japanese carriers and many naval aviators, and what is generally agreed to have been the turning point of the Pacific War.
The Question
All four of the code systems used by Admiral Yamamoto had been broken in the fall of 1941 and were used by Station Hypo located at Pearl Harbor. The message intercepted at Station H on November 24th was translated and forwarded directly to Washington DC by Station Hypo, bypassing the local Hawaiian commanders. Washington DC did not relay the translated message back to Kimmell and Short, but instead sent an immediate order to Admiral Kimmell to terminate Exercise 191, a fleet preparedness exercise operating northwest of Hawaii directly in the path of the oncoming Japanese Striking fleet. Kimmell was ordered back to Pearl Harbor.
On November 25th, Winston Churchill sent an urgent message to President Roosevelt. Of all the messages sent between Churchill and Roosevelt, only the message of November 25th remains classified on the grounds of "National Security". On November 28th, USS Enterprise was ordered out of Pearl Harbor in company with 11 of the Unites States’ newest warships, ostensibly to deliver aircraft to Wake Island. On December 5th, USS Lexington was ordered out of Pearl Harbor in company with 8 of the Unites States’ newest warships, ostensibly to deliver aircraft to Midway Island. When the Japanese attack hit Pearl Harbor, the targets they found were older relics from a bygone age; the 21 modern ships of the Pacific fleet, including the two carriers, were safely out of harm’s way.
Background and biographical information is from Wikipedia articles on:
Japanese Naval Codes that can be found at…
http://en.wikipedia.org/wiki/Japanese_naval_codes
Station HYPO that can be found at…
http://en.wikipedia.org/wiki/Station_Hypo
Events Leading to Pearl Harbor Attack that can be found at…
http://en.wikipedia.org/wiki/Events_leading_to_the_attack_on_Pearl_Harbor
Also see…
Japanese Codebreaking at Blechley Park…
http://www.mkheritage.co.uk/bpt/JapCDSCH1.html
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