Category Archives: U.S.

Okinawan Emigration Destinations

From Liminality of the Japanese Empire: Border Crossings from Okinawa to Colonial Taiwan, by Hiroko Matsuda (U. Hawaii Press, 2018), Kindle loc. ~840:

Before migration to the US mainland became popular in Okinawa, anti-Japanese sentiment spread across the West Coast, where the Japanese population had increased rapidly at the turn of the twentieth century. After the enactment of the Gentlemen’s Agreement in 1908, Okinawans were unable to enter the United States as migrant laborers. Thus, very few Okinawans followed the thousands of Japanese who had migrated to the US mainland. The few who did so during this period were youths pursuing higher education. Some went to the US mainland via Hawai‘i, Canada, and Mexico; a few traveled directly from Okinawa. As the Gentlemen’s Agreement allowed only families of migrants to enter for the purpose of reuniting with husbands and fathers, some female Okinawans arranged to immigrate and join their grooms in the United States as picture brides.

Elderly Okinawans have a saying that best sums up these migration trends: “The richest people were able to immigrate to South America; people with some money migrated to the Philippines; and the poorest worked on mainland Japan.” Indeed, when it proved too difficult to enter the United States as migrant workers, the Japanese turned to South America—especially Brazil—and the Philippines as alternative destinations. Later, the South Sea Islands [Micronesia] became popular as the South Seas Development Company (Nan’yō Kōhatsu) targeted and recruited Okinawan laborers for its sugar industry. While Brazil, the Philippines, and the South Sea Islands were under different governments and Okinawan immigrants there worked in different industries, there are some commonalities among them. First, the initial immigrants in these countries worked in manufacturing and commercial crop industries such as coffee (Brazil), abaca [aka “manila hemp”]  (the Philippines), and sugarcane (the South Sea Islands). Second, Okinawan immigrants accounted for the majority of Japanese immigrant communities in these countries despite their treatment as “second-class Japanese” and “the other Japanese.”

Japan sent the first indentured migrant farmworkers to Brazil in 1908. Okinawans accounted for more than 40 percent, 325 of the 781 immigrants, of that inaugural group of economic immigrants to Brazil. In fact, many of the first Okinawan immigrants left the plantations to which they were allocated shortly after their arrival. This gave a negative impression to both the Japanese and Brazilian governments. In 1913, the Japanese government refused to accept Okinawans wishing to travel to Brazil as indentured laborers, citing their propensity to leave the plantations and their cultural difference from Japanese workers from the other prefectures, but when migration agencies were unable to recruit enough laborers from the other prefectures, Okinawans were once again permitted to go to Brazil as indentured migrant workers. However, as was the case in the United States, Okinawan migration to Brazil was prohibited in 1919, and only immigrants who were currently in Brazil were allowed to send for their families.

In addition to Brazil, Okinawa sent a significant number of immigrants to other Latin American countries. For instance, Peru quickly became one of the most popular destinations for Okinawan migrant workers after the first group of Okinawan immigrants arrived there in 1899. Between 1899 and 1941, Okinawa sent 11,461 immigrants to Peru, accounting for nearly 30 percent of the total number of Japanese immigrants. Although the immigrants were initially employed on plantation farms, many later moved to urban areas, where they became grocery store or restaurant owners.

Similarly, most Japanese immigrants to Argentina were Okinawans. This is despite the fact that Japanese immigrants had been arriving in Argentina since 1910. There were 1,831 Okinawans in Argentina in 1940, accounting for approximately 45 percent of the Japanese population in the country. Not all Okinawans in Argentina had migrated directly from Okinawa; in actuality, many ended up in Argentina after traveling to Brazil and Peru. In Argentina, many Okinawans initially found work as factory laborers or porters. A sizeable number eventually set up small businesses such as coffee shops and laundries.

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Filed under Argentina, Brazil, Canada, economics, Hawai'i, industry, Japan, labor, Mexico, Micronesia, migration, nationalism, Peru, Philippines, U.S.

German U-Boat Losses, 1943-44

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 280-281:

After the carnage of 1942 and early 1943, the Allies had seen a stunning turnaround in the Atlantic. By September 1943, most U-boats had been swept from the Atlantic waters. This was thanks not only to the new high-speed bombes but also to a host of other Allied war measures: advances in radar, sonar, and high-frequency direction finding; more aircraft carriers and long-range aircraft; better convoy systems. The Allies changed their convoy cipher, and Dönitz could no longer read it. The tables turned. During the summer, American hunter-killer units used code breaking along with other intelligence to find and sink big German submarines that were sent out to refuel U-boats. These refuelers were known as milch cows, and between June and August, American carrier planes sank five. In October, they finished off all but one. The refuelers were critical to the U-boats’ ability to stay so far away from their home base, and as the milch cows went down, the U-boats began to drift homeward.

There was always the chance, however, that the U-boats could come back. And they did try. In October 1943, the U-boats reappeared. But now the costs were punishingly high. For every Allied merchant vessel sunk, seven U-boats were lost. Now Dönitz was the one who could not build boats fast enough to replace those he was losing. In November, thirty U-boats ventured into the North Atlantic and sank nothing. The U-boats began lurking elsewhere, clustering around the coast of Britain, hoping to intercept materiel brought in for an anticipated invasion of France. Dönitz was always trying to innovate the U-boats, adding a Schnorchel that enabled them to remain submerged longer. He was willing to sacrifice his boats, and his men, and kept the U-boats in the water even as a way to tie up Allied resources.

But it was a losing battle. In May 1944, the Allies sank half the U-boats in operation—more than the Germans could replace. More than three-quarters of the U-boat crews were killed, suffering terrible watery deaths. The women in the tracking room were privy to the full immensity and horror.

By now the British had indeed handed over the four-rotor bombe operations to the Americans. After the war, a U.S. Navy file was made of messages from grateful—and gracious—British colleagues. “Congratulations from Hut six on colossal… week,” said one missive from Bletchley. An internal British memo acknowledged that “by half way through 1944” the Americans “had taken complete control of Shark and undoubtedly knew far more about the key than we did.”

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Japanese Shipping Losses, 1943-44

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 249, 250-251:

November 1943, one month after Dot’s arrival at Arlington Hall, marked the war’s most devastating month for Japanese tonnage sunk. U.S. subs sank forty-three ships and damaged twenty-two. American sub captains received intelligence of seventy-six movements of enemy ships. In December, American subs sank or damaged about 350,000 tons, including thirty-two ships sunk and sixteen damaged.

Behind the success of the U.S. Navy were the code breakers. “The success of undersea warfare is to a certain extent due to the success with which Japanese code messages were translated,” noted a naval report. An American naval commander pointed out in a postwar memo that sometimes a convoy might slip through, but only because U.S. submarines were kept so busy by information from decoded messages that they could not handle all the convoys they were alerted to. Over at the Naval Annex, the assembly line of WAVES identified the movements of marus [merchant marine ships] supplying the Japanese Navy. Findings from both operations found their way to the submarine captains, who could hardly keep up with the bounty of intelligence.

The devastation of Japan’s shipping had an enormous impact. Soldiers were deprived of food and medicine. Aircraft did not get spare parts and could not launch missions. Troops did not reach the places they were sent as reinforcements. On March 12, 1944, a broken 2468 message gave the route and schedule of the Twenty-First Wewak Transport convoy, sunk while leaving Wewak to return to Palau. When the Japanese Eighteenth Area Army made a “complete tabulation of shipping from Rabaul and Truk during January,” in an attempt to convince Japanese Army headquarters that it was feasible to send them much-needed supplies, these messages laid out the shipping routes and sealed their doom. Only 50 percent of ships reached the destination; only 30 percent got home.

At the end of the war, a U.S. naval report found that “more than two-thirds of the entire Japanese merchant marine and numerous warships, including some of every category, were sunk. These sinkings resulted, by mid-1944, in isolation of Japan from her overseas sources of raw materials and petroleum, with far reaching effects on the capability of her war industry to produce and her armed forces to operate. Her outlying bases were weakened by lack of reinforcements and supplies and fell victim to our air, surface and amphibious assaults; heavy bombers moved into the captured bases.” This report’s author, C. A. Lockwood, commander of the submarine force of the U.S. Pacific Fleet, noted that his men got a “continuous flow of information on Japanese naval and merchant shipping, convoy routing and composition, damage sustained from submarine attacks, anti-submarine measures employed or to be employed, effectiveness of our torpedoes, and a wealth of other pertinent intelligence.” Whenever code breaking was unavailable, he added, “its absence was keenly felt. The curve of enemy contacts and of consequent sinkings almost exactly paralleled the curve of volume of Communication Intelligence available.”

He added: “There were many periods when every single U.S. sub in the Pacific was busy” responding.

In fact, he added, code-breaking intelligence made it seem to the Japanese that there were more American submarines in the Pacific than there really were. “In early 1945 it was learned from a Japanese prisoner of war that it was [a] common saying in Singapore that you could walk from that port to Japan on American periscopes. This feeling among the Japanese was undoubtedly created, not by the great number of submarines on patrol, but rather by the fact, thanks to communications intelligence, that submarines were always at the same place as Japanese ships.”

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Japanese Transport Code Language

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 244-246:

The language of the 2468 [transport code] messages was telegraphic in style. Short, straightforward, and no-nonsense, the messages consisted of sailing schedules, harbormaster reports, reports on the water levels of ports and transportation of cargo. Sailing schedules were the simplest. These included the transport number, the date, the time the maru [ship name] would be arriving or leaving, and its destination. Others concerned the movement of troops or equipment. A few dealt with transportation of the wounded or ashes of the dead. The marus out there in the Pacific Ocean carried everything: food, oil, supplies, human remains.

When a new message arrived, Dot looked for stereotypes, which were words that occurred frequently in the same place. “Maru” was a common one, but there were others as well, depending on the origin and the goods being transported. For example, one station transmitting from Singapore—the #3 Sen San Yusoo—sent a regular report on the shipping of oil to Hiroshima, Manila, and Tokyo. Stereotyped words might include ship names and numbers; the number of kiloliters of light oil, crude oil, heavy oil, aviation gasoline, or other gasoline aboard; how many trips each ship would take, and when. Another Singapore station transmitted to Hiroshima, Tokyo, and Moji a report of ships leaving for Palembang. Stereotypes might include the ship number or name, the date and hour of departure, the speed, the course, and the date and hour of scheduled arrival at the mouth of the Musi River.

Another transmitted a daily weather report with data including wind velocity and direction, temperature, and condition of the surface of the Andaman Sea, the South China Sea, the Yellow Sea, and other faraway bodies of water. Dot handled a lot of weather reports. Sitting at her table in Arlington, Virginia, Dot was amused at how many bits and pieces of information she knew about what the weather was like eight thousand miles away.

Another station transmitted a report on small boats available for supply services. Mentioned might be steel barges, wooden barges, special boats, small boats, twenty-metric-ton boats, plywood barges, and cargo submarines.

A station at Surabaya originated a report on the departure of ships escorted by a single Navy plane, including the names and types of ships (motor, sail, fishing), number of barges being towed, date of departure and destination, speed, scheduled date of arrival, route, and daily position of ship on consecutive days at given hours. A report from Shanghai about a supply ship might include a message spelling out that the probable route was “from Shanghai along the coast to the Yangtze River up the Yangtze River to WUU (Buko) down the river to Nanking and finally across the East China Sea to Moji.”

Here is how Dot did her work: Let’s say she knew that the code group for “arriving” was 6286 and she knew where this word was likely to appear. She would find that place in the message and look at the GAT [“group as transmitted”] before her. Books at Arlington Hall listed common code words as well as possible enciphered versions. She would look for a match, or she could do the math in her head and strip out the additive herself. Sometimes—when they were desperate—the code breakers would take the code groups and encipher them with every possible additive. A smattering of 2468 code groups included:

4333 hassoo—to send things [発送]
4362 jinin—personnel [人員]
4400 kaisi—beginning, commencing [開始]
4277 kookoo—navigate, to sail [航行]
4237 toochaku yotei—scheduled to arrive [到着予定]
4273 hatsu yotei—scheduled to leave [発予定]

There were vocabulary words associated with sailing schedules. According to training materials compiled at Arlington Hall, atesaki [宛先] was “destination” or “address”; chaku [着] was “arriving”; dai ichi [第一] was “first”; honjitsu [本日] was “today.” Maru [丸] was “commercial ship”; sempakutu [船舶通] was “ship” [-tu for 通行 tsuukou ‘traffic, passage’?]; sempakutai [船舶隊] was “convoy unit”; teihaku [碇泊] was “anchoring”; yori [より] was “from”; yotei [予定] was “schedule.” Gunkan [軍艦] was “warship.” Chu [中] was “now [or ‘in the middle of, i.e., underway’].” Hatsusen [発船] was “ship leaving.” Hi [日] was “day”; hongetsu [本月] was “this month”; senghu [sic; 船上 senjou?] was “onboard ship”; shuzensen [修繕船] was “ship being repaired”; tosai sen [搭載船] was “ship loading.”

Dot’s workday consisted of messages that, once deciphered, said things like “PALAU DENDAI/ 2/ 43/ T.B./ TRANSPORT/ 918/ (/878/)/ 20th/ 18/ JI/ CHAKU/ ATESAKI/ DAVAO/ SEMPAKUTAI/ 4/ CEBU/ E.T./”

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Occupied Germany as Ethnic Wastebasket

From Orderly and Humane: The Expulsion of the Germans after the Second World War, by R. M. Douglas (Yale U. Press, 2012), Kindle pp. 192-193:

As 1946, the year of “organized expulsions,” began drawing to a close, each of the Big Three was feeling the strain. “At present,” Colonel Thicknesse warned, “we tend to regard occupied Germany as a waste-paper basket with a limitless capacity for the unwanted waste of the world. We are not convinced that this attitude is correct, either economically or politically.” According to figures reported to CRX [= Combined Repatriation Executive], by November the Soviet zone had admitted more than 1.8 million expellees from Poland and Czechoslovakia; the U.S. zone approximately 1.7 million from Czechoslovakia and Hungary (including 160,000 who had arrived via Austria); and the British zone more than 1.3 million from the Recovered Territories: a cumulative total of almost five million people. To this figure could be added a number which could not be precisely calculated—but certainly one in the hundreds of thousands for each occupation zone—of Volksdeutsche who had made their way under duress out of their countries of origin, but entered Germany as unregistered “infiltrees.” All were arriving in a country whose urban centers the Western Allies had gone to immense trouble and expense during the previous five years to level to the ground, an endeavor in which they had enjoyed considerable success and which had left Germany with “a worse housing problem than has ever before existed in any area of comparable size and population.” Even after every available camp, military base, school, church, barn, air raid shelter, and, in some cases, cave had been filled with expellees, the onrushing human tide continued to overwhelm the best efforts of the rudimentary German administration upon whose shoulders the occupying forces thrust the responsibility. As a rule, according to reception officers in all three occupation zones, the expellees were arriving in possession of little more than the—usually insufficient—clothing in which they stood. The overwhelming majority were women and children. Few could make any meaningful contribution in the short term to their own support. Hundreds of thousands needed immediate care, in hospitals, old-age homes, orphanages, or residential centers for the disabled, though the shortage of resources meant that a great many would not receive it.

This was not at all how the Allies had envisaged the population transfers when they had been sold on the idea during the war. Then the stated rationale had been to remove a cohort of “dangerous” Germans—above all, fit men of military age—who might threaten the security of the countries in which they lived. Instead, it had been the least dangerous Germans who had been deported, while the fit men were being held back for forced labor, and in many cases pressured to take out Polish or Czechoslovak nationality against their will. The occupying powers thus found themselves presented with a first-class social, economic, and humanitarian crisis that threatened to undo whatever plans they had made for German reconstruction, as well as to disrupt the economies of the expelling states for years to come. Predictably, each of the Big Three with the benefit of experience discovered its enthusiasm for this novel method of “stabilizing” the European continent shrinking to the vanishing point. After coping—or failing to cope—with the “wild expulsions” of 1945, and finding the “organized expulsions” of 1946 from their perspective to be less satisfactory yet, each of the Allied powers entered 1947 with the same overriding objective: to put an end to what was proving an intolerable burden to it as quickly as possible.

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Cracking the Japanese Water Transport Code

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 241-242:

Ambon. Canton. Davao. Haiphong. Hankow. Kiska. Kobe. Kuching. Kupang. Osaka. Palembang. Rabaul. Saigon. Takao. Wewak. Dot Braden until a few months earlier had never heard of most of these places. Now they ruled her life. They kept her running from the big table where she worked, over to the overlapper’s console, then back again to her spot at the big table. These were the names of places, somewhere in Asia or the South Pacific, likely to be mentioned toward the beginning of messages coded in 2468, the main Japanese water-transport code, or one of the other, smaller transport codes.

Or rather, they were some of the places. Transport code 2468 was massive; 2468 was everywhere; 2468 dominated the Pacific Ocean. Anything anybody needed was sent by water. Water was how the rice was transported, and the soldiers, and the spare airplane parts. To move the goods the Japanese Army needed, the marus were always sailing. Always leaving and arriving. A maru [丸] could be a tanker, a freighter, a cargo ship, a barge, a cable layer, a motor transport. [Japanese Navy ship names never use maru.] They plied between Hiroshima, Yokohama, Wewak, Saipan, Tokyo, Manila, the Truk Lagoon. Exotic places. It was not necessary for Dot to know how to pronounce the cities and ports, but it was helpful to know the four-digit code groups that stood for them. Code system 2468 commanded Dot’s attention, controlled Dot’s movements. It filled her brain.

A job more unlike teaching Virginia schoolchildren would be hard to imagine. No longer was Dot Braden standing at a chalkboard, explaining physics formulas to eye-rolling teenagers, or ordering senior girls to march and salute. Instead, she was sitting head down at a table puzzling over words she had never heard before she came to Arlington Hall. “Sono.” “Indicator.” “Discriminant.” “GAT.” The sono [‘that, aforementioned’] was the number appended to messages that had been divided into parts before being transmitted. Sono #1 was the first part, Sono #2 was the second part, and so on. The discriminant was the number that identified the system—for instance, 2468. The indicator was the tiny clue that told you what book to look in. GAT stood for “group as transmitted”: the code group plus the cipher. The GATs were what you saw when you looked at the message for the first time.

Dot, of course, was not to utter any of these words outside the high wire double fences of the Arlington Hall compound. People were warned never to use, outside the building, the words they used inside it. “This material is extremely secret and must be treated with the utmost care,” one training document said. “Some of the words which you will consider elementary have been used only in this code, eg KAIBOTSU SU ‘to sink a ship’ [海没す ‘sea-reject do’?]. If you should mention this word to any one connected with the Axis or in some way succeed in letting it get into improper hands, this one fact alone would betray to the Japanese that we are reading their most recent transport code.”

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Culture of U.S. Army Codebreakers, 1943

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 207-209:

Unlike the Navy operation, the Army’s code-breaking operation at Arlington Hall was polyglot, open-minded, and nonhierarchical. Anybody could be in charge of anything. There was a wide assortment of ages and backgrounds working at its wooden tables. Bespectacled middle-aged men labored alongside pin-curled young women with names like Emerald and Velvet. Which is not to say that there wasn’t sexist condescension: One of the bookish men, a New York editor named William Smith, referred to Arlington Hall’s contingent of female southern workers as the “Jewels.” It was a lofty and rather snide reference to the number of women working there whose parents had seen fit to name them after precious stones. He wasn’t wrong: In addition to a profusion of Opals and Pearls, the workforce included a real Jewel—Jewel Hogan—who worked in the machine section. And there was Jeuel Bannister, the band director recruited out of South Carolina.

At Arlington Hall there also were “BIJs,” or born-in-Japans, the term for people who grew up in missionary families and worked in the translating section. There was the actor Tony Randall—later famous as Felix Unger in The Odd Couple—clowning around (at one point he danced on a table) as he waited for the intelligence summary to be taken to the Pentagon. There was an extended group of siblings and cousins—the Erskines—who had relocated as a family unit from Ohio. There was Sumner Redstone, the future billionaire media magnate, now a young officer in the translating unit. There was Julia Ward, former dean of students at Bryn Mawr, czar of a well-run library unit. There were nannies, beauticians, secretaries, restaurant hostesses. Josephine Palumbo at eighteen was virtually running the personnel unit, plucked out of McKinley High School in Washington. Tiny Jo Palumbo, daughter of an Italian immigrant laborer, was the person who swore in newcomers, and the sight of her administering the grave secrecy oath had inspired one code breaker to write a lyrical poem in her honor.

Unlike the Navy, Arlington Hall also had an African American code-breaking unit. This was not so much because the place was unusually liberal-minded, but rather because Eleanor Roosevelt—or somebody at the top—had declared that 12 to 15 percent of the Arlington Hall workforce should be black. It was poor recompense for the fact that many of Arlington’s black residents had been pushed out of their homes by the construction of the Pentagon and other military edifices, but work was welcome and this was better than nothing. Arlington Hall’s African American workers had to take segregated transport to get there, and many, even those who were college graduates, were given menial jobs as janitors and messengers. But there also was a special code-breaking unit whose existence was unknown to many of the white workers. The African American unit monitored the enciphered communications of companies and banks to see what was being transmitted in the global private sector and who was doing business with Hitler or Mitsubishi. They kept a library of 150 systems, with careful files of addresses and characteristics of all the world’s main commercial codes. There was no shortage of qualified people to staff it: Despite its segregated school system and the inequality of resources that accompanied segregation, the city of Washington had a number of highly regarded black public schools, as well as Howard, one of the country’s premier historically black universities. One of the team members, Annie Briggs, started out as a secretary and rose to head the production unit. Another, Ethel Just, led the expert translators. The team was led by a black man, William Coffee, who studied English at Knoxville College in Tennessee, started out as a janitor and waiter at Arlington Hall, and rose to this position.

In short, in its eclecticism and, often, its eccentricity, the atmosphere at Arlington Hall was unlike anything the U.S. military had ever produced.

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Code-breaking Triumph in the Solomons, 1943

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 200-201:

The Navy women had just missed taking part in the code-breaking triumph at Midway, but ten months later they were fully embedded for, and actively engaged in, the other great code-breaking event of the Pacific naval war. On April 13, 1943, a message came through along the E-14 channel of JN-25, addressed to “Solomons Defense Force, Air Group 204, AirFlot 26, Commander Ballale Garrison Force.” The code breakers weren’t able to recover the whole message right away, but the fragments they did recover suggested that the commander in chief of the combined fleet—Admiral Yamamoto himself—was headed to Ballale Island (now Balalae) on April 18. Intelligence officers concluded that this was an inspection tour.

The initial break was made in the Pacific, but Washington also got busy, recovering additives and code groups so that blanks could be filled in. More messages were intercepted, and the fast-working, far-flung teams exchanged findings. Among those digging out code recoveries was Fran Steen from Goucher. The inter-island cipher JN-20 “carried further details” about Yamamoto’s upcoming trip, so Raven’s crew of women were busy as well, adding facts and insights. Together the code breakers were able to reconstruct Yamamoto’s precise itinerary, which called for a day of hops between Japanese bases in the Solomon Islands and New Britain. Their translation concluded that the commander would “depart RR (Rabaul) at 0600 in a medium attack plane escorted by six fighters; arrive RXZ (Ballale) at 0800”; depart at 1100 and land at RXP (Buin) at 1110; leave there at 1400 and return to Rabaul at 1540, traveling by plane and, at one point, minesweeper. He would be conducting an inspection tour and visiting the sick and wounded.

It was an extraordinary moment. The Americans knew exactly where the enemy’s most valuable—and irreplaceable—naval commander would be, and when. Yamamoto was known for punctuality. Far above the pay grade of those working additive recovery, Nimitz and other top war officials decided Yamamoto would be shot down. It was not a light decision, assassinating an enemy commander, but they made it. The itinerary, as one memo later put it, signed the admiral’s “death warrant.”

In what was known as Operation Vengeance, sixteen U.S. Army fighter planes, Lockheed P-38s, went into the air on April 18, taking off from a Guadalcanal airfield. They knew Yamamoto would be flying in a Japanese bomber the Americans called a Betty, escorted by Zero fighter planes. The Americans calculated their own flight plan to meet the route they anticipated Yamamoto would be taking, planning to encounter him over Bougainville. They flew for so long that the pilots were getting drowsy; the white coastline of Bougainville was racing beneath them when one of the pilots broke radio silence and shouted, “Bogeys! Eleven o’clock!” There they were, on the horizon: six Zeros, two Bettys. The Japanese did not see the Americans at first, but once they did, the escorting Zeros moved to block the U.S. fighter planes, firing so the bombers could escape. There was a hectic battle in which it never became clear who had shot down whom, but one Betty bomber plummeted into the trees, the other into the surf. Yamamoto’s body was found in the Bougainville jungle, his white-gloved hand clutching his sword.

Cheering broke out at the Naval Annex when they heard the news. The architect of the Pearl Harbor attack was dead. The payback felt complete.

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Cracking the Japanese Navy Code System, 1940s

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 88-90:

On June 1, 1939, the Japanese fleet began using a code that the Allies came to call JN-25. The Japanese—who had moved to using numbers rather than characters—now employed a massive codebook containing about thirty thousand five-digit groups. They also had a new way of enciphering. Before the code was sent, each code group was enciphered by using math to apply an “additive.”

Here is how the additive method worked: When a Japanese cryptographer began encoding a single message, he would look in the codebook and find the five-digit group that stood for the word (or syllable or phrase or punctuation mark) he wanted. He would repeat that process until he got to the end of the message. Then he would get out a different book, called an additive book, turn to a page—selected at random—pick a five-digit number, and add that to the first code group. He would add the next additive to the second. And so on. The Japanese code makers used a peculiar kind of math called noncarrying or “false” addition. There was no carrying of digits, so 8 plus 7 would equal 5, rather than 15. If the code group for “maru” was, say, 13563, and the additive was 24968, the resulting group would be 37421 (1 + 2 =3; 3 + 4 = 7; 5 + 9 = 4; 6 + 6 = 2; 3 + 8 = 1). That was the group of digits that would be radioed. To crack a message, the Americans had to figure out the additive and subtract it to get the code group. Then they had to figure out what the code group stood for.

Once again, it was Agnes Driscoll who diagnosed the new system. Neither she nor anybody in the Navy operation had seen an additive cipher—everything up to then had been transposition, or switching—but she figured it out. It took her less than a year to make a dent. A March 1 status report for the unit “GYP-1” stated that for the “5-number system”—an early title for JN-25—“First break [was] made by Mrs. Driscoll. Solution progressing satisfactorily.” She worked on it for several more months before being transferred in late 1940 to German systems—a promotion in the sense that the Atlantic was beginning to emerge as the hot spot. The research team continued working their way through JN-25, using her methods.

The process of stripping additives and discerning the meaning of code groups was laborious and excruciating. Years after World War II ended, American code breakers who worked in Hawaii and Australia were still arguing with their D.C. counterparts over what certain code groups stood for. Much like the women who trained the men who would get to do the wartime flying, much like Elizebeth Friedman over at the Coast Guard, Agnes Driscoll taught the men in the field who did this. “In the Navy she was without peer as a cryptanalyst,” wrote Edwin Layton, who headed naval intelligence for Admiral Nimitz, the chief naval commander in the Pacific during the war. In December 1940, both code and cipher were changed, to a system the Allies called JN-25B; the team stripped the additives and built a partial bank of code words. Then, in early December 1941—days before Pearl Harbor—the additive books were changed. The codebooks were not. The U.S. Navy was able to recover a certain amount of the new system—but not enough—before the attack on Pearl Harbor happened and all hell broke loose.

“If the Japanese Navy had changed the code-book along with the cipher keys on 1 December 1941, there is no telling how badly the war in the Pacific would have gone,” said Laurance Safford.

As crushing as Pearl Harbor was, it was thanks in large part to Driscoll’s decades-long detective work—and to the example Elizebeth Friedman set for other women—that America did not enter the Second World War quite as blind as it might have seemed.

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Two Methods of Encryption

From Code Girls, by Liza Mundy (Hachette, 2017), Kindle pp. 82-83:

Technically, there are two kinds of secret message systems. One kind is a code, in which an entire word or phrase is replaced by another word, a series of letters, or a string of numbers, known as a “code group.” A code may be used for secrecy, but also for brevity and truncation. Shorthand is a code in precisely this way and so, often, is modern-day texting. Common phrases, even long ones, can be compressed into short code groups, making messages faster and—when using cable, as many people did in the early decades of the twentieth century—cheaper to send. Saving money has always been important to governments, so the compression advantage is a big deal. Cable companies typically charged by the word, so the fact that stock phrases like “your request of last month has been approved” could be boiled down to a code group, as could the names of places or people or units, meant governments could save a good bit of money when sending telegrams. In the War Department’s “general address and signature” code that was employed in 1925, for example, the word “cavalry” was HUNUG, “Pursuit Squadron” was LYLIV, “Bombardment Squadron” was BEBAX, “Wagon Company” was DIGUF, “U.S. Naval Academy” was HOFOW, and “Fourth Division Air Service” was BABAZ. (Texting uses codes, like OMG and IMO, for much the same reason: brevity and, at times, concealment.) The best code is one in which code groups are randomly assigned, with no rhyme or reason that an enemy can discern. Codes are compiled and kept in codebooks, not unlike dictionaries, where the encoder can look up the word or phrase and the corresponding group that stands for it. But even random codes have an obvious vulnerability: Constant repetitious use of the same code groups in messages enables code breakers to tease out their meaning from context or position.

The other type of system is called a cipher, in which a single letter—or number—is replaced by another single letter or number. Ciphers can be created by scrambling letters, which is called transposition—turning the word “brain,” for example, into “nirab.” Or a cipher can be achieved by replacing individual units with other units, a method called substitution: By substituting X for b, T for r, V for a, O for i, and P for n, for example, brain becomes “XTVOP.” For centuries, ciphers were created by hand, often by those clever Renaissance men who would line alphabets up against one another and create boxes and tables that gave a way to substitute one letter for another. But when radio and telegraph came along, messages could be sent much, much faster than a wigwag flag could do. Machines were needed that could encipher rapidly; and, because it became easier to spot simple patterns when so many messages were being sent and intercepted, more complicated ciphers were needed. People can make complex ciphers, but people make mistakes. Machines are less likely to do so. These machines created an early form of what would later be called encryption, which meant that people who broke them might be described as an early version of what would later be called hackers.

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