computer science

Japanese army and diplomatic codes

Japanese army and diplomatic codes is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Japanese army and diplomatic codes rather than just read about it. In short: Japanese army and diplomatic codes. This article is on Japanese army and diplomatic ciphers and codes used up to and during World War II, to supplement the article on Japanese naval codes.

Key takeaways

Japanese army and diplomatic codes belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Japanese army and diplomatic codes to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Japanese army and diplomatic codes from memory before moving on to harder problems.

Reference excerpt

Japanese army and diplomatic codes. This article is on Japanese army and diplomatic ciphers and codes used up to and during World War II, to supplement the article on Japanese naval codes. The diplomatic codes were significant militarily, particularly those from diplomats in Germany. Japanese army (IJA) and diplomatic codes were studied at Arlington Hall (US), Bletchley Park (UK), Central Bureau or CBB (Australian, US; in Melbourne, then Brisbane), the FECB (British Far East Combined Bureau) at Hong Kong, Singapore, Kilindi then Colombo and the British Wireless Experimental Centre in Delhi.

Japanese Army codes and ciphers Arlington Hall had initially delayed study of the Army codes until 1942 because of the "high payoff" from diplomatic codes, but were not successful until 1943. Then, with success on Army codes in April, the increasing workload was put under Solomon Kullback in branch B-II in September. Other mainly diplomatic work was put under Frank Rowlett in B-III. Branch B-I translated Japanese. Initially, "brute-force" IBM runs on Army codes from April 1942 to the end of the year did not work. but U.S. Army Sgt. Joe Richard noticed that the system for 2468 changed every three weeks, so the messages could be arranged by IBM tabulators by group and time period. Richard was assisted at Central Bureau by Major Harry Clark and by the head, Abraham "Abe" Sinkov, and broke 2468 on 6 April 1943, for which he was awarded the Legion of Merit. Wilfrid Noyce at the Wireless Experimental Centre had realised that the first letter of the third group of each message was not random and that other groups were paired in "doublets". At first, Arlington Hall could not find the non-randomness until Richard told them it changed about every four weeks. With this tip Arlington Hall broke the code, as did the Wireless Experimental Centre. It used a 10×10 conversion square with the plaintext digits 0-9 across the top, key digits down the side, and the table contained the cipher text digits. As well as "kana", the Chinese Telegraph Code was used to explain places or words, and the code groups 1951 or 5734 indicated that the CTC follows; an "absurd security flaw" as it was like "Stop" as a key. The CTC code group was often preceded by the "kana" groups for the same character.

Main Army codes Many of the Army codes were known to the Allies by their four-figure discriminant numbers. The SIS at Arlington Hall gave them three-letter codes, e.g., JEM. A conference at Arlington Hall in early 1944 decided on the allocation of high-level army codes.

2345 Army Ordnance System or JEN 2468 Water Transport Code senpaku angoshu 2 a super-enciphered code or JEK 3366 Army Air Force General Purpose Code 3636 Air Safety Service Code koku hoan angoo-sho No 1 5555 North Pacific System 5678 or ATRW the main Army system to early (May) 1942, then split into 2345 and 7890 6633 Army Air General Purpose Code, Burma (variant of 3366) 6666 Philippine System, old; used by cut-off units in 1944 7777 South-West Pacific System 7890 Army General Administrative System or JEM BULBUL an Army air-to-ground reciphered code kuuchi renraku kanji-hyoo 2-goo.

Water Transport Code The Army Water Transport Code senpaku angoshu 2 (2468 or JEK) was used by the Water Transport organization, the Army's own Navy, when moving troops around the Pacific. Ships signalled their noontime position, course, speed and other movement items. As the Japanese relied extensively on sea transport for isolated garrisons, the information assisted in planning air raids and action against Japanese air raids, and, through the American Seventh Fleet, submarine attacks. Breaking it in 1943 gave the Allies insight into other Army codes.

BULBUL A three-figure reciphered air-to-ground code used by the IJA, kuuchi renraku kanji-hyoo 2-goo was known to the British as BULBUL. First broken by the Bletchley Park air section, it provided vital tactical information, so work on it was carried out in India at the Wireless Experimental Centre in Delhi. Traffic from the army operational flying units based around Meiktila in Burma was particularly valuable, aided by a book and some additive sheets from a Japanese aircraft shot down over India. By November 1944 many messages predicting air raids were intercepted, decoded and sent out as intelligence in ninety minutes. On one occasion Allied night fighters got the lot and all night we could hear Mingaladon air base calling for its lost children.

Find of Japanese Army records In January 1944, Mainline Japanese Army codes were broken with help from a buried trunk found during the Battle of Sio in New Guinea by Australian troops of the 9th Division. The records had been left by retreating Japanese Army troops of the 20th Division. Tokyo was told the papers had been burnt, but the Japanese lieutenant did not want to reveal his position by burning them, so they were buried in a metal strongbox near a stream. They included the army codebook Rikugun Angosho Number Four, which was fed into Sinkov's IBM machines; two additive books and codes for traffic identifiers 2345, 5555, 6666, 7777 and 7870, which were now readable; and an instruction book on how to use the other books. The Central Bureau spent a day drying the damp pages, and the flood of decoded messages that ensued meant that MacArthur had to ask the U.S. Navy for assistance. Two translators, Forrest Biard and Thomas Mackie were sent from Fleet Radio Unit, Melbourne (FRUMEL). Major Sinkov and his team of Americans and Australians from Central Bureau photographed every dried page and sent these photocopies immediately to Arlington Hall, the headquarters of the U.S. Army Signal Intelligence Service, for decryption. The Allies went from decrypting only 1,846 Japanese Army messages in January 1944 to 36,000 messages in March. This intelligence windfall was so beneficial to MacArthur that he accelerated the timetable and the Admiralty Islands campaign began immediately in late February followed by the joint invasions of Hollandia and Aitape, far behind enemy lines, in late April. The Admiralty Islands campaign was originally scheduled to begin in June 1944 prior to the Japanese Army codes being broken.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Japanese army and diplomatic codes

Start with the simplest possible case. Write down what Japanese army and diplomatic codes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Japanese army and diplomatic codes before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Japanese army and diplomatic codes ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Japanese army and diplomatic codes

In research: Japanese army and diplomatic codes appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Japanese army and diplomatic codes in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Japanese army and diplomatic codes is common in secondary-school and first-year university syllabi. It links to neighbouring topics History of cryptography, Imperial Japanese Army, Intelligence operations, so understanding it makes those chapters shorter.
In everyday life: Look for Japanese army and diplomatic codes outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Japanese army and diplomatic codes in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Japanese army and diplomatic codes means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Japanese army and diplomatic codes out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Japanese army and diplomatic codes in simple terms?

Japanese army and diplomatic codes. This article is on Japanese army and diplomatic ciphers and codes used up to and during World War II, to supplement the article on Japanese naval codes.

Why does Japanese army and diplomatic codes matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Japanese army and diplomatic codes?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Japanese army and diplomatic codes.