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112-542: 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. The Red Book code was an IJN code book system used in World War I and after. It was called "Red Book" because the American photographs made of it were bound in red covers. It should not be confused with

224-537: A columnar transposition . By November 1942, they were able to read all previous traffic and break each message as they received it. Enemy shipping, including troop convoys, was thus trackable, exposing it to Allied attack. Over the next two weeks they broke two more systems, the "previously impenetrable" JN167 and JN152. The "minor operations code" often contained useful information on minor troop movements. A simple transposition and substitution cipher used for broadcasting navigation warnings. In 1942 after breaking JN-40

336-521: A 34-year-old U.S. Navy lieutenant named Laurance F. Safford was assigned to expand OP-20-G's domain to radio interception. He worked out of Room 2646, on the top floor of the Navy Department building in Washington, D.C. Japan was of course a prime target for radio interception and cryptanalysis , but there was the problem of finding personnel who could speak Japanese . The Navy had

448-591: A 500-ton galleon -type ship that transported the Japanese embassy of Hasekura Tsunenaga to the Americas, which then continued to Europe. From 1604 the Bakufu also commissioned about 350 Red seal ships , usually armed and incorporating some Western technologies, mainly for Southeast Asian trade. For more than 200 years, beginning in the 1640s, the Japanese policy of seclusion (" sakoku ") forbade contacts with

560-539: A Chinese naval force near Korean island of Pungdo , damaging a cruiser, sinking a loaded transport, capturing one gunboat and destroying another. This battle occurred before war was officially declared on 1 August 1894. On 10 August, the Japanese ventured into the Yellow Sea to seek out the Beiyang Fleet, and subsequently bombarded both Weihaiwei and Port Arthur. Finding only small vessels in both harbors,

672-644: A ban on Wakō piracy; the pirates then became vassals of Hideyoshi, and comprised the naval force used in the Japanese invasion of Korea (1592–1598) . Japan built her first large ocean-going warships in the beginning of the 17th century, following contacts with the Western nations during the Nanban trade period . In 1613, the daimyō of Sendai , in agreement with the Tokugawa Bakufu , built Date Maru ,

784-532: A cauldron in Ningbo . Japan undertook major naval building efforts in the 16th century, during the Warring States period when feudal rulers vying for supremacy built vast coastal navies of several hundred ships. Around that time Japan may have developed one of the first ironclad warships when Oda Nobunaga , a daimyō , had six iron-covered Oatakebune made in 1576. In 1588 Toyotomi Hideyoshi issued

896-538: A combination of heavily armed large warships, with smaller and more innovative offensive units permitting aggressive tactics. As a result of the conflict, under the Treaty of Shimonoseki (April 17, 1895), Taiwan and the Pescadores Islands were transferred to Japan. The Imperial Japanese Navy took possession of the island and quelled opposition movements between March and October 1895. Japan also obtained

1008-657: A decisive encounter at sea, the Japanese decided to send more troops to Korea. Early in September, the Japanese navy was directed to initiate further landings and to support the army on Korea's western coast. As Japanese ground forces moved north to attack Pyongyang, Admiral Ito correctly guessed that the Chinese would attempt to reinforce their army in Korea by sea. On 14 September, the Combined Fleet sailed north to search

1120-407: A document to the daijō-kan titled "Opinions Regarding Naval Expansion" asserting that a strong navy was essential to maintaining the security of Japan. In furthering his argument, Iwakura suggested that domestic rebellions were no longer Japan's primary military concern and that naval affairs should take precedence over army concerns; a strong navy was more important than a sizable army to preserve

1232-560: A draw, and neither side gained decisive control of the sea, army units in Korea would concentrate on maintaining preexisting positions. Lastly, if the Combined Fleet was defeated and consequently lost command of the sea, the bulk of the army would remain in Japan and prepare to repel a Chinese invasion, while the Fifth Division in Korea would be ordered to dig in and fight a rearguard action. A Japanese squadron intercepted and defeated

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1344-520: A force of at least six large battleships, supplemented by four armored cruisers of at least 7,000 tons. The centerpiece of this expansion was to be the acquisition of four new battleships, in addition to two that were already being completed in Britain as part of an earlier construction program. Yamamoto was also advocated the construction of a balanced fleet. OP-20-G OP-20-G or "Office of Chief Of Naval Operations ( OP NAV), 20 th Division of

1456-596: A large part because of Satsuma power, influence, and patronage. Between 19 August and 23 November 1882, Satsuma forces with Iwakura's leadership, worked tirelessly to secure support for the Navy's expansion plan. After uniting the other Satsuma members of the Dajokan, Iwakura approached the emperor the Meiji emperor arguing persuasively just as he did with the Dajokan, that naval expansion was critical to Japan's security and that

1568-486: A lesser naval power) would dispatch a portion of its fleet against Japan. Yamamoto therefore calculated that four battleships would be the most likely strength of any seagoing force that a major power could divert from their other naval commitments to use against Japan, and he also believed that two more battleships might be contributed to such a naval expedition by a lesser hostile power. In order to achieve victory in such an engagement, Yamamoto theorized that Japan should have

1680-671: A lieutenant commander if over 35). But control was by "regular military types". The Navy wanted the Army to forbid civilians to touch the SIGABA cipher machine like the Navy; though it was developed by a civilian ( William Friedman ). A Royal Navy visitor and intercept specialist Commander Sandwith reported in 1942 on "the dislike of Jews prevalent in the US Navy (while) nearly all the leading Army cryptographers are Jews". In 1940, SIS and OP-20-G came to agreement with guide lines for handling MAGIC;

1792-762: A military force to defeat the rebels, culminating with the Naval Battle of Hakodate in May 1869. The Imperial side took delivery (February 1869) of the French-built ironclad Kotetsu (originally ordered by the Tokugawa shogunate) and used it decisively towards the end of the conflict. In February 1868 the Imperial government had placed all captured shogunate naval vessels under the Navy Army affairs section. In

1904-685: A minimal role transporting troops from western to eastern Japan. Only the Battle of Awa (28 January 1868) was significant; this also proved one of the few Tokugawa successes in the war. Tokugawa Yoshinobu eventually surrendered after the fall of Edo in July 1868, and as a result most of Japan accepted the emperor's rule, however resistance continued in the North . On 26 March 1868 the first naval review in Japan took place in Osaka Bay , with six ships from

2016-606: A modern fleet, so that by 1885 cost overruns had jeopardized the entire 1883 plan. Furthermore, increased costs coupled with decreased domestic tax revenues, heightened concern and political tension in Japan regarding funding naval expansion. In 1883, two large warships were ordered from British shipyards. The Naniwa and Takachiho were 3,650 ton ships. They were capable of speeds up to 18 kn (33 km/h; 21 mph) and were armed with 54 to 76 mm (2 to 3 in) deck armor and two 260 mm (10 in) Krupp guns. The naval architect Sasō Sachū designed these on

2128-515: A number of officers who had served in a diplomatic capacity in Japan and could speak Japanese fluently, but there was a shortage of radiotelegraph operators who could read Japanese Wabun code communications sent in kana . Fortunately, a number of US Navy and Marine radiotelegraph operators operating in the Pacific had formed an informal group in 1923 to compare notes on Japanese kana transmissions. Four of these men became instructors in

2240-505: A peak of activity during the 16th and 17th centuries at a time of cultural exchange with European powers during the Age of Discovery . After two centuries of stagnation during the country's ensuing seclusion policy under the shōgun of the Edo period , Japan's navy was comparatively antiquated when the country was forced open to trade by American intervention in 1854. This eventually led to

2352-490: A result tensions began to rise between the two countries over competing interests in Korea. The Japanese naval leadership was generally cautious and even apprehensive at the prospect of hostilities with China, as the navy had not yet received several modern warships that had been ordered in February 1893, particularly the battleships Fuji and Yashima and the cruiser Akashi . Hence, initiating hostilities at this time

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2464-473: A single hypothetical enemy individually, but also to confront any fleet from two combined powers that might be dispatched against Japan from overseas waters. He assumed that given their conflicting global interests, it was highly unlikely that the United Kingdom and Russia would ever join together in a war against Japan, instead considering it more likely that a major power like Russia (in alliance with

2576-422: A single powerful main gun, the 320 mm (13 in) Canet gun . Altogether, Bertin supervised the building of more than 20 units. They helped establish the first true modern naval force of Japan. It allowed Japan to achieve mastery in the building of large units, since some of the ships were imported, and some others were built domestically at the arsenal of Yokosuka: This period also allowed Japan "to embrace

2688-466: A supportive role to drive an invading enemy from the coast. The resulting military organization followed the Rikushu Kaijū (Army first, Navy second) principle. This meant a defense designed to repel an enemy from Japanese territory, and the chief responsibility for that mission rested upon Japan's army; consequently, the army gained the bulk of the military expenditures. During the 1870s and 1880s,

2800-465: A thirty-four-man British naval mission, headed by Lt. Comdr. Archibald Douglas , arrived in Japan. Douglas directed instruction at the Naval Academy at Tsukiji for several years, the mission remained in Japan until 1879, substantially advancing the development of the navy and firmly establishing British traditions within the Japanese navy from matters of seamanship to the style of its uniforms and

2912-492: A total of 50) and delivered the largest contingent of troops among the intervening nations (20,840 Imperial Japanese Army and Navy soldiers, out of a total of 54,000). The conflict allowed Japan to engage in combat alongside Western nations and to acquire first-hand understanding of their fighting methods. Following the war against China, Japan was pressured into renouncing its claim to the Liaodong Peninsula in

3024-537: The 1860 Japanese delegation to the United States . In 1865 the French naval engineer Léonce Verny was hired to build Japan's first modern naval arsenals, at Yokosuka and Nagasaki . The shogunate also allowed and then ordered various domains to purchase warships and to develop naval fleets, Satsuma , especially, had petitioned the shogunate to build modern naval vessels. A naval center had been set up by

3136-577: The Battle of Midway in 1942. JN-25 is the name given by codebreakers to the main, and most secure, command and control communications scheme used by the IJN during World War II. Named as the 25th Japanese Navy system identified, it was initially given the designation AN-1 as a "research project" rather than a "current decryption" job. The project required reconstructing the meaning of thirty thousand code groups and piecing together thirty thousand random additives. Introduced from 1 June 1939 to replace Blue (and

3248-517: The JN-40 merchant-shipping code. Important for information on troop convoys and orders of battle. An inter-island cipher that provided valuable intelligence, especially when periodic changes to JN-25 temporarily blacked out U.S. decryption. JN-20 exploitation produced the "AF is short of water" message that established the main target of the Japanese Fleet, leading to a decisive U.S. victory at

3360-610: The Liaodong Peninsula , although was later forced by Russia, Germany and France to return it to China ( Triple Intervention ), only for Russia take possession of it soon after. The Imperial Japanese Navy further intervened in China in 1900 by participating, together with Western Powers, in the suppression of the Chinese Boxer Rebellion . The Japanese navy supplied the largest number of warships (18 out of

3472-743: The Meiji Restoration . Accompanying the re-ascendance of the Emperor came a period of frantic modernization and industrialization . The IJN saw several successes in combat during the early twentieth century, sometimes against much more powerful enemies, such as in the Sino-Japanese War and the Russo-Japanese War , before being largely destroyed in World War II. Japan has a long history of naval interaction with

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3584-501: 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 attaché in 1923; after three years of work Agnes Driscoll

3696-873: The Royal Navy and the United States Navy (USN). It was supported by the Imperial Japanese Navy Air Service for aircraft and airstrike operations from the fleet. It was the primary opponent of the Western Allies in the Pacific War . The origins of the Imperial Japanese Navy date back to early interactions with nations on the Asian continent , beginning in the early feudal period and reaching

3808-545: The Saga Rebellion (1874) and especially the Satsuma Rebellion (1877), forced the government to focus on land warfare, and the army gained prominence. Naval policy, as expressed by the slogan Shusei Kokubō (literally: "Static Defense"), focused on coastal defenses, on a standing army (established with the assistance of the second French Military Mission to Japan ), and a coastal navy that could act in

3920-462: The whale factory ship Nisshin Maru No. 2 (1937) visited San Francisco, U.S. Customs Service Agent George Muller and Commander R. P. McCullough of the U.S. Navy's 12th Naval District (responsible for the area) boarded her and seized her codebooks, without informing Office of Naval Intelligence (ONI). Copies were made, clumsily, and the originals returned. The Japanese quickly realized JN-39

4032-460: The 1854 Convention of Kanagawa led to the opening of Japan to international trade and interaction. This was soon followed by the 1858 Treaty of Amity and Commerce and treaties with other powers . As soon as Japan opened up to foreign influences, the Tokugawa shogunate recognized the vulnerability of the country from the sea and initiated an active policy of assimilation and adoption of Western naval technologies. In 1855, with Dutch assistance,

4144-640: The Army agreed that they would supply the White House in January, March, May, July, September and November and the Navy in February, April, June, August, October and December. But in May 1941 MAGIC documents were found in the desk of Roosevelt's military aide Edwin "Pa" Watson and the Navy took over; while the Army provided MAGIC to the State Department instead. The result was that much of the MAGIC

4256-515: The Army was responsible on even-numbered days and the Navy on odd-numbered days. So, on the first minute after midnight on 6 December 1941 the Navy took over. But USN Lt-Comdr Alwin Kramer had no relief officer (unlike the Army, with Dusenbury and Bratton); and that night was being driven around by his wife. He was also responsible for distributing MAGIC information to the President; in January 1941

4368-410: The Army's SIS but Commander Joseph Wenger had picked out the "perfect new home" for the rapidly expanding OP-20-G and commandeered a private girls' school Mount Vernon College for Women for $ 800,000 (a fraction of what the buildings and grounds were worth), in 1944, compensated $ 1.038 million. So on 7 February 1943 it opened at what was called the "Naval Communications Annex", and staff moved in over

4480-637: The Asian continent, involving transportation of troops between Korea and Japan, starting at least with the beginning of the Kofun period in the 3rd century. Following the attempts at Mongol invasions of Japan by Kubilai Khan in 1274 and 1281, Japanese wakō became very active in plundering the coast of China . In response to threats of Chinese invasion of Japan, in 1405 the shogun Ashikaga Yoshimitsu capitulated to Chinese demands and sent twenty captured Japanese pirates to China, where they were boiled in

4592-530: The Boshin War. Enomoto Takeaki, the admiral of the shōgun ' s navy, refused to surrender all his ships, remitting just four vessels, and escaped to northern Honshū with the remnants of the shōgun ' s navy: eight steam warships and 2,000 men. Following the defeat of pro-shogunate resistance on Honshū, Admiral Enomoto Takeaki fled to Hokkaidō , where he established the breakaway Republic of Ezo (27 January 1869). The new Meiji government dispatched

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4704-461: The Combined Fleet returned to Korea to support further landings off the Chinese coast. The Beiyang Fleet, under the command of Admiral Ding, was initially ordered to remain close to the Chinese coast while reinforcements were sent to Korea by land. However, as Japanese troops swiftly advanced northward from Seoul to Pyongyang, the Chinese decided to rush troops to Korea by sea under a naval escort in mid-September. Concurrently, because there not yet been

4816-476: The Dutch flag. Frictions with the foreign ships, however, started from the beginning of the 19th century. The Nagasaki Harbour Incident involving HMS  Phaeton in 1808, and other subsequent incidents in the following decades, led the shogunate to enact an Edict to Repel Foreign Vessels . Western ships, which were increasing their presence around Japan due to whaling and the trade with China, began to challenge

4928-544: The European Theater." A cipher machine used by the Imperial Japanese Navy from late 1942 to 1944 and similar to CORAL. A succession of codes used to communicate between Japanese naval installations. These were comparatively easily broken by British codebreakers in Singapore and are believed to have been the source of early indications of imminent naval war preparations. The Fleet Auxiliary System, derived from

5040-550: The FECB at Kilindini broke JN-152 and the previously impenetrable JN-167, another merchant shipping cypher. A merchant-shipping cipher (see JN-152). In June 1942 the Chicago Tribune , run by isolationist Col. Robert R. McCormick , published an article implying that the United States had broken the Japanese codes, saying the U.S. Navy knew in advance about the Japanese attack on Midway Island, and published dispositions of

5152-537: The French during the Boshin War. Also, Japan was uneasy with being dependent on Great Britain, at a time when Great Britain was very close to China. The Meiji government issued its First Naval Expansion bill in 1882, requiring the construction of 48 warships, of which 22 were to be torpedo boats. The naval successes of the French Navy against China in the Sino-French War of 1883–85 seemed to validate

5264-533: The Greater Japanese Empire', or 日本海軍 Nippon Kaigun , 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, when it was dissolved following Japan's surrender in World War II . The Japan Maritime Self-Defense Force (JMSDF) was formed between 1952 and 1954 after the dissolution of the IJN. The Imperial Japanese Navy was the third largest navy in the world by 1920, behind

5376-527: The Imperial Japanese Navy remained an essentially coastal-defense force, although the Meiji government continued to modernize it. Jo Sho Maru (soon renamed Ryūjō Maru ) commissioned by Thomas Glover was launched at Aberdeen , Scotland on 27 March 1869. In 1870 an Imperial decree determined that Britain's Royal Navy should serve as the model for development, instead of the Netherlands navy. In 1873

5488-733: The Japanese bombs had smashed the US Navy 's fleet at anchor in Pearl Harbor . In February 1942 power struggles within the Navy resulted in the sidelining of Laurance Safford , with the support of Admirals Ernest King and Richmond K. Turner (and Joseph Redman ) for the centralizing of control of naval intercept and codebreaking in Washington. So two new sections were headed by John R. Redman (Communications Combat Intelligence section) and Joseph Wenger (Communications Cryptanalytical section; to handle decryption and translation). Safford

5600-625: The Japanese invasion fleet. The executive officer of Lexington , Commander Morton T. Seligman (who was transferred to shore duties), had shown Nimitz's executive order to reporter Stanley Johnston . The government at first wanted to prosecute the Tribune under the Espionage Act of 1917 . For various reasons, including the desire not to bring more attention to the article and because the Espionage Act did not cover enemy secrets,

5712-518: The Japanese judged that a protracted war with China would increase the risk of intervention by the European powers with interests in East Asia. The army's Fifth Division would land at Chemulpo on the western coast of Korea, both to engage and push Chinese forces northwest up the peninsula and to draw the Beiyang Fleet into the Yellow Sea, where it would be engaged in decisive battle. Depending upon

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5824-494: The Japanese political and military leadership, and Japan began to build up its military strength in preparation for future confrontations. The political capital and public support that the navy gained as a result of the recent conflict with China also encouraged popular and legislative support for naval expansion. In 1895, Yamamoto Gombei was assigned to compose a study of Japan's future naval needs. He believed that Japan should have sufficient naval strength to not only deal with

5936-442: The Japanese state. Furthermore, he justified that a large, modern navy, would have the added potential benefit of instilling Japan with greater international prestige and recognition, as navies were internationally recognized hallmarks of power and status. Iwakura also suggested that the Meiji government could support naval growth by increasing taxes on tobacco, sake, and soy. After lengthy discussions, Iwakura eventually convinced

6048-427: The Korean and Chinese coasts and bring the Beiyang Fleet to battle. On 17 September 1894, the Japanese encountered the Beiyang Fleet off the mouth of the Yalu River . The Beiyang Fleet was crippled during the ensuing battle , in which the Chinese lost eight out of 12 warships. The Chinese subsequently withdrew behind the Weihaiwei fortifications. However, they were then surprised by Japanese troops, who had outflanked

6160-413: The Ministry of War was replaced by a separate Army Ministry and Navy Ministry. In October 1873, Katsu Kaishū became Navy Minister. After the consolidation of the government the new Meiji state set about to build up national strength. The Meiji government honored the treaties with the Western powers signed during the Bakumatsu period with the ultimate goal of revising them, leading to a subsided threat from

6272-408: The Office of Naval Communications, G Section / Communications Security", was the U.S. Navy 's signals intelligence and cryptanalysis group during World War II . Its mission was to intercept, decrypt, and analyze naval communications from Japanese , German , and Italian navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the section's effort

6384-444: The Pearl Harbor attack, but because the Japanese Navy was not engaged in significant battle operations before then, there was little traffic available to use as raw material. Before then, IJN discussions and orders could generally travel by routes more secure than broadcast, such as courier or direct delivery by an IJN vessel. Publicly available accounts differ, but the most credible agree that the JN-25 version in use before December 1941

6496-574: The Philippines, and the British Far East Combined Bureau in Singapore, and using a punched card tabulating machine manufactured by International Business Machines , a successful attack was mounted against the 4 December 1941 edition (JN25b). Together they made considerable progress by early 1942. "Cribs" exploited common formalities in Japanese messages, such as "I have the honor to inform your excellency" (see known plaintext attack ). Later versions of JN-25 were introduced: JN-25c from 28 May 1942, deferred from 1 April then 1 May; providing details of

6608-412: The Russian-led Triple Intervention. The Japanese were well aware that they could not compete with the overwhelming naval power possessed by the three countries in East Asian waters, particularly Russia. Faced with little choice, the Japanese ceded the peninsula back to China for an additional 30 million taels (roughly ¥45 million). The cession of the Liaodong Peninsula was seen as a humiliation by

6720-468: The Satsuma domain in Kagoshima, students were sent abroad for training and a number of ships were acquired. The domains of Chōshū , Hizen , Tosa and Kaga joined Satsuma in acquiring ships. These naval elements proved insufficient during the Royal Navy 's Bombardment of Kagoshima in 1863 and the Allied bombardments of Shimonoseki in 1863–64. By the mid-1860s the shogunate had a fleet of eight warships and thirty-six auxiliaries. Satsuma (which had

6832-461: The U.S. Navy's signals intelligence command, OP-20-G ; at Pearl Harbor it was centered at the Navy's Combat Intelligence Unit ( Station HYPO , also known as COM 14), led by Commander Joseph Rochefort . However, in 1942 not every cryptogram was decoded, as Japanese traffic was too heavy for the undermanned Combat Intelligence Unit. With the assistance of Station CAST (also known as COM 16, jointly commanded by Lts Rudolph Fabian and John Lietwiler) in

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6944-548: The US Secretary of State, Cordell Hull , at 1:00 PM Washington time that negotiations between the United States and Japan were ended. The embassy was then to destroy their cipher machines. This sounded like war, and although the message said nothing about any specific military action, Kramer also realized that the sun would be rising over the expanses of the central and western Pacific by that time. The two men both tried to get in touch with Army Chief of Staff General George C. Marshall . After some agonizing delays, Marshall got

7056-433: The Western technological and scientific revolution which allowed Japan to remain aware of naval sciences, such as cartography , optics and mechanical sciences. Seclusion, however, led to the loss of any naval and maritime traditions the nation possessed. Apart from Dutch trade ships, no other Western vessels were allowed to enter Japanese ports. A notable exception was during the Napoleonic wars when neutral ships flew

7168-401: The army and saw naval strength as paramount. In 1870 the new government drafted an ambitious plan to develop a navy with 200 ships organized into ten fleets. The plan was abandoned within a year due to lack of resources. Financial considerations were a major factor restricting the growth of the navy during the 1870s. Japan at the time was not a wealthy state. Soon, however, domestic rebellions,

7280-432: The art of reading kana transmissions when the Navy began conducting classes in the subject in 1928. The classes were conducted by the Room 2426 crew, and the radiotelegraph operators became known as the "On-The-Roof Gang". By June 1940, OP-20-G included 147 officers, enlisted men, and civilians, linked into a network of radio listening posts as far-flung as the Army's. OP-20-G did some work on Japanese diplomatic codes, but

7392-414: The attacks on Midway and Port Moresby. JN-25d was introduced from 1 April 1943, and while the additive had been changed, large portions had been recovered two weeks later, which provided details of Yamamoto's plans that were used in Operation Vengeance , the shooting-down of his plane. This was a naval code used by merchant ships (commonly known as the " maru code"), broken in May 1940. 28 May 1941, when

7504-424: The attitudes of its officers. From September 1870, the English Lieutenant Horse, a former gunnery instructor for the Saga fief during the Bakumatsu period, was put in charge of gunnery practice on board the Ryūjō . In 1871, the ministry resolved to send 16 trainees abroad for training in naval sciences (14 to Great Britain, two to the United States), among whom was Heihachirō Tōgō. In 1879, Commander L. P. Willan

7616-519: The call-sign system, starting with the new JN-25c codebook (issued two months before). However the changes indicated the Japanese believed the Allies had worked out the fleet details from traffic analysis or had obtained a codebook and additive tables, being reluctant to believe that anyone could have broken their codes (least of all a Westerner). Imperial Japanese Navy The Imperial Japanese Navy ( IJN ; Kyūjitai : 大日本帝國海軍 Shinjitai : 大日本帝国海軍 Dai-Nippon Teikoku Kaigun 'Navy of

7728-439: The charges were dropped. A grand jury investigation did not result in prosecution but generated further publicity and, according to Walter Winchell , "tossed security out of the window". Several in Britain believed that their worst fears about American security were realized. In early August, a RAN intercept unit in Melbourne ( FRUMEL ) heard Japanese messages, using a superseded lower-grade code. Changes were made to codebooks and

7840-416: The decrypts and methodically examined them. He realized their importance and sent a warning to field commanders, including Major General Walter Short , the Army commander in Hawaii. However, Marshall was reluctant to use the telephone because he knew that telephone scramblers weren't very secure and sent it by less direct channels. Due to various constraints and bumblings, Short got the message many hours after

7952-436: The dispatch of a large force of the Imperial Japanese Navy. As a result, the Japan–Korea Treaty of 1876 was signed, marking the official opening of Korea to foreign trade, and Japan's first example of Western-style interventionism and adoption of "unequal treaties" tactics. In 1878, the Japanese cruiser Seiki sailed to Europe with an entirely Japanese crew. After the Imo Incident in July 1882, Iwakura Tomomi submitted

8064-435: The domains had returned their lands and population registers to the government. In 1871 the domains were abolished altogether and as with the political context the centralization of the navy began with the domains donating their forces to the central government. As a result, in 1871 Japan could finally boast a centrally controlled navy, this was also the institutional beginning of the Imperial Japanese Navy. In February 1872,

8176-470: The early phase of the Boshin War of 1868–1869. All other naval vessels remained under the control of the various domains which had been acquired during the Bakumatsu period. The naval forces mirrored the political environment of Japan at the time: the domains retained their political as well as military independence from the Imperial government. Katsu Kaishū a former Tokugawa navy leader, was brought into

8288-481: The following months, military forces of the government came under the control of several organizations which were established and then disbanded until the establishment of the Ministry of War and of the Ministry of the Navy of Japan in 1872. For the first two years (1868–1870) of the Meiji state no national, centrally controlled navy existed, – the Meiji government only administered those Tokugawa vessels captured in

8400-447: The government as Vice Minister of the Navy in 1872, and became the first Minister of the Navy from 1873 until 1878 because of his naval experience and his ability to control Tokugawa personnel who retained positions in the government naval forces. Upon assuming office Katsu Kaishu recommended the rapid centralization of all naval forces – government and domain – under one agency. The nascent Meiji government in its first years did not have

8512-449: The harbor's defenses in coordination with the navy. The remnants of the Beiyang Fleet were destroyed at Weihaiwei . Although Japan had emerged victorious at sea, the two large German-made Chinese ironclad battleships ( Dingyuan and Zhenyuan ) had remained almost impervious to Japanese guns, highlighting the need for bigger capital ships in the Imperial Japanese Navy. The next step of the Imperial Japanese Navy's expansion would thus involve

8624-528: The largest domain fleet) had nine steamships, Choshu had five ships plus numerous auxiliary craft, Kaga had ten ships and Chikuzen eight. Numerous smaller domains also had acquired a number of ships. However, these fleets resembled maritime organizations rather than actual navies with ships functioning as transports as well as combat vessels; they were also manned by personnel who lacked experienced seamanship except for coastal sailing and who had virtually no combat training. The Meiji Restoration in 1868 led to

8736-462: The line of the Elswick class of protected cruisers but with superior specifications. An arms race was taking place with China however, who equipped herself with two 7,335 ton German-built battleships ( Ting Yüan and Chen-Yüan ). Unable to confront the Chinese fleet with only two modern cruisers, Japan resorted to French assistance to build a large, modern fleet which could prevail in

8848-483: The most powerful domains as the government did not have enough naval power to put down the rebellion on its own. Although the rebel forces in Hokkaidō surrendered, the government's response to the rebellion demonstrated the need for a strong centralized naval force. Even before the rebellion the restoration leaders had realized the need for greater political, economic and military centralization and by August 1869 most of

8960-472: The most recent descendant of the Red code), it was an enciphered code, producing five-numeral groups for transmission. New code books and super-enciphering books were introduced from time to time, each new version requiring a more or less fresh cryptanalytic attack. John Tiltman with some help from Alan Turing (at GCSB, Government Communications Security Bureau ) had "solved" JN25 by 1941, i.e. they knew that it

9072-409: The navy secured the ¥6.5 million required annually to support an eight-year expansion plan, this was the largest that the Imperial Japanese Navy had secured in its young existence. However, naval expansion remained a highly contentious issue for both the government and the navy throughout much of the 1880s. Overseas advances in naval technology increased the costs of purchasing large components of

9184-456: The necessary political and military force to implement such a policy and so, like much of the government, the naval forces retained a decentralized structure in most of 1869 through 1870. The incident involving Enomoto Takeaki's refusal to surrender and his escape to Hokkaidō with a large part of the former Tokugawa Navy's best warships embarrassed the Meiji government politically. The imperial side had to rely on considerable naval assistance from

9296-438: The numbers in the codebook were divisible by three. "Breaking" rather than "solving" a code involves learning enough code words and indicators so that any given message can be read. In particular, JN-25 was significantly changed on 1 December 1940 (JN25a); and again on 4 December 1941 (JN25b), just before the attack on Pearl Harbor . British, Australian, Dutch and American cryptanalysts co-operated on breaking JN-25 well before

9408-619: The order of a revolutionary torpedo boat, Kotaka , which was considered the first effective design of a destroyer, in 1887 and with the purchase of Yoshino , built at the Armstrong works in Elswick , Newcastle upon Tyne , the fastest cruiser in the world at the time of her launch in 1892. In 1889, she ordered the Clyde-built Chiyoda , which defined the type for armored cruisers . Between 1882 and 1918, ending with

9520-700: The organization's primary focus was on Japanese military codes. The US Navy first got a handle on Japanese naval codes in 1922, when Navy agents broke into the Japanese consulate in New York City , cracked the safe, took photographs of pages of a Japanese navy codebook, and left, having put everything back as they had found it. Before the war, the Navy cipher bureau operated out of three main bases: The US Army Signal Intelligence Service (SIS) and OP-20-G were hobbled by bureaucracy and rivalry, competing with each other to provide their intelligence data, codenamed " MAGIC ", to high officials. Complicating matters

9632-455: The outcome of this engagement, Japanese decisionmakers anticipated that they would be faced with one of three choices. If the Combined Fleet were to win decisively at sea, the larger part of the Japanese army could immediately land in force on the Korean coast between Shanhaiguan and Tianjin in order to defeat the Chinese army and bring the war to a swift conclusion. If the naval engagement was

9744-526: The outside world and prohibited the construction of ocean-going ships on pain of death. Contacts were maintained, however, with the Dutch through the port of Nagasaki , the Chinese also through Nagasaki and the Ryukyus and Korea through intermediaries with Tsushima. The study of Western sciences, called " rangaku " through the Dutch enclave of Dejima in Nagasaki led to the transfer of knowledge related to

9856-468: The overthrow of the shogunate. From 1868, the newly formed Meiji government continued with reforms to centralize and modernize Japan. Although the Meiji reformers had overthrown the Tokugawa shogunate, tensions between the former ruler and the restoration leaders led to the Boshin War (January 1868 to June 1869). The early part of the conflict largely involved land battles, with naval forces playing

9968-565: The potential of torpedo boats, an approach which was also attractive to the limited resources of Japan. In 1885, the new Navy slogan became Kaikoku Nippon (Jp:海国日本, "Maritime Japan"). In 1885, the leading French Navy engineer Émile Bertin was hired for four years to reinforce the Japanese Navy and to direct the construction of the arsenals of Kure and Sasebo . He developed the Sankeikan class of cruisers; three units featuring

10080-459: The private domain navies of Saga , Chōshū, Satsuma , Kurume , Kumamoto and Hiroshima participating. The total tonnage of these ships was 2,252 tons, which was far smaller than the tonnage of the single foreign vessel (from the French Navy) that also participated. The following year, in July 1869, the Imperial Japanese Navy was formally established, two months after the last combat of

10192-595: The revolutionary new technologies embodied in torpedoes , torpedo-boats and mines , of which the French at the time were probably the world's best exponents". Japan acquired its first torpedoes in 1884, and established a "Torpedo Training Center" at Yokosuka in 1886. These ships, ordered during the fiscal years 1885 and 1886, were the last major orders placed with France. The unexplained sinking of Unebi en route from France to Japan in December 1886, created embarrassment however. Japan turned again to Britain, with

10304-423: The ruling coalition to support Japan's first multi-year naval expansion plan in history. In May 1883, the government approved a plan that, when completed, would add 32 warships over eight years at a cost of just over ¥26 million. This development was very significant for the navy, as the amount allocated virtually equaled the navy's entire budget between 1873 and 1882. The 1882 naval expansion plan succeeded in

10416-424: The sea. This however led to conflict with those disgruntled samurai who wanted to expel the westerners and with groups which opposed the Meiji reforms. Internal dissent – including peasant uprisings – become a greater concern for the government, which curtailed plans for naval expansion as a result. In the immediate period from 1868 many members of the Meiji coalition advocated giving preference to maritime forces over

10528-592: The seclusion policy. The Morrison Incident in 1837 and news of China's defeat during the Opium War led the shogunate to repeal the law to execute foreigners, and instead to adopt the Order for the Provision of Firewood and Water. The shogunate also began to strengthen the nation's coastal defenses. Many Japanese realized that traditional ways would not be sufficient to repel further intrusions, and western knowledge

10640-649: The shogunate acquired its first steam warship, Kankō Maru , and began using it for training, establishing a Naval Training Center at Nagasaki. Samurai such as the future Admiral Enomoto Takeaki (1836–1908) was sent by the shogunate to study in the Netherlands for several years. In 1859 the Naval Training Center relocated to Tsukiji in Tokyo . In 1857 the shogunate acquired its first screw-driven steam warship Kanrin Maru and used it as an escort for

10752-472: The standing army of forty thousand men was more than sufficient for domestic purposes. While the government should direct the lion's share of future military appropriations toward naval matters, a powerful navy would legitimize an increase in tax revenue. On November 24, the emperor assembled select ministers of the daijō-kan together with military officers, and announced the need for increased tax revenues to provide adequate funding for military expansion, this

10864-457: The upcoming conflict. During the 1880s, France took the lead in influence, due to its " Jeune École " ("young school") doctrine, favoring small, fast warships, especially cruisers and torpedo boats , against bigger units. The choice of France may also have been influenced by the Minister of the Navy, who happened to be Enomoto Takeaki at that time (Navy Minister 1880–1885), a former ally of

10976-574: The visit of the French Military Mission to Japan , the Imperial Japanese Navy stopped relying on foreign instructors altogether. In 1886, she manufactured her own prismatic powder , and in 1892 one of her officers invented a powerful explosive, the Shimose powder . Japan continued the modernization of its navy, especially driven by Chinese efforts to construct a powerful modern fleet with foreign (especially German) assistance, and as

11088-476: Was a five-digit code with a codebook to translate words into five digits and there was a second "additive" book that the sender used to add to the original numbers "But knowing all this didn’t help them read a single message". By April 1942 JN25 was about 20 percent readable, so codebreakers could read "about one in five words" and traffic analysis was far more useful. Tiltman had devised a (slow; neither easy nor quick) method of breaking it and had noted that all

11200-681: Was able to break the additive portion of the code. Knowledge of the Red Book code helped crack the similarly constructed Blue Book code. A cipher machine developed for Japanese naval attaché ciphers, similar to JADE. It was not used extensively, but Vice Admiral Katsuo Abe , a Japanese representative to the Axis Tripartite Military Commission, passed considerable information about German deployments in CORAL, intelligence "essential for Allied military decision making in

11312-491: Was compromised, and replaced it with JN-40. JN-40 was originally believed to be a code super-enciphered with a numerical additive, in the same way as JN-25. However, in September 1942, an error by the Japanese gave clues to John MacInnes and Brian Townend, codebreakers at the British FECB , Kilindini . It was a fractionating transposition cipher based on a substitution table of 100 groups of two figures each followed by

11424-426: Was delayed or unused. There was no efficient process for assessing and organizing the intelligence, as was provided postwar by a single intelligence agency. In the early hours of the morning of 7 December 1941, the U.S. Navy communications intercept station at Fort Ward on Bainbridge Island, Washington , picked up a radio message being sent by the Japanese government to the Japanese embassy in Washington, D.C. It

11536-526: Was directed towards Japan and included breaking the early Japanese "Blue" book fleet code . This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific , Atlantic , and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington, D.C. The Code and Signal Section was formally made a part of the Division of Naval Communications (DNC), as Op-20-G, on July 1, 1922. In January 1924,

11648-466: Was followed by an imperial re-script. The following month, in December, an annual ¥7.5-million tax increase on sake, soy, and tobacco was fully approved, in the hopes that it would provide ¥3.5 million annually for warship construction and ¥2.5 million for warship maintenance. In February 1883, the government directed further revenues from other ministries to support an increase in the navy's warship construction and purchasing budget. By March 1883,

11760-645: Was hired to train naval cadets. Ships such as the Fusō , Kongō and Hiei were built in British shipyards, and they were the first warships built abroad specifically for the Imperial Japanese Navy. Private construction companies such as Ishikawajima and Kawasaki also emerged around this time. During 1873, a plan to invade the Korean Peninsula , the Seikanron proposal made by Saigō Takamori ,

11872-735: Was narrowly abandoned by decision of the central government in Tokyo. In 1874, the Taiwan expedition was the first foray abroad of the new Imperial Japanese Navy and Army after the Mudan Incident of 1871 , however the navy served largely as a transport force. Various interventions in the Korean Peninsula continued in 1875–1876, starting with the Ganghwa Island incident provoked by the Japanese gunboat Un'yō , leading to

11984-402: Was not more than perhaps 10% broken at the time of the attack, and that primarily in stripping away its super-encipherment. JN-25 traffic increased immensely with the outbreak of naval warfare at the end of 1941 and provided the cryptographic "depth" needed to succeed in substantially breaking the existing and subsequent versions of JN-25. The American effort was directed from Washington, D.C. by

12096-459: Was perceived as ill-advised, and the navy was far less confident than their counterparts in the Japanese army about the outcome of a war with China. Japan's main strategy was to swiftly obtain naval superiority, as this was critical to the success of operations on land. An early victory over the Beiyang fleet would allow Japan to transport troops and material to the Korean Peninsula; additionally,

12208-519: Was shifted to an administrative support and cryptographic research role; thus was sidelined for the remainder of the war, as ultimately was Joseph Rochefort in Hawaii. With Japanese advances in the Philippines , a possible invasion of Hawaii, and greater demand for intelligence, OP-20-G undertook two courses of action: In Summer 1942 the Navy went through the motions of perhaps co-locating with

12320-558: Was that the Coast Guard , the FBI , and even the FCC also had radio-intercept operations. The Navy organization at OP-20-G was more conventionally hierarchical than the Army at Arlington Hall which went more on merit rather than rank (like Bletchley Park), though commissions were handed out to "civilians in uniform" with rank according to age (an ensign for 28 or under, a lieutenant to 35 or

12432-485: Was the last in a series of 14 messages that had been sent over the previous 18 hours. The messages were decrypted by a PURPLE analogue machine at OP-20-G and passed to the SIS for translation from Japanese, early on the morning of December 7. Army Colonel Rufus S. Bratton and Navy Lieutenant Commander Alwin Kramer independently inspected the decrypts. The decrypts instructed the Japanese ambassador to Washington to inform

12544-497: Was utilized through the Dutch at Dejima to reinforce Japan's capability to repel the foreigners; field guns, mortars, and firearms were obtained, and coastal defenses reinforced. Numerous attempts to open Japan ended in failure, in part to Japanese resistance, until the early 1850s. During 1853 and 1854, American warships under the command of Commodore Matthew Perry , entered Edo Bay and made demonstrations of force requesting trade negotiations. After two hundred years of seclusion,

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