The Fog of War:

American Perceptions of the Japanese Battleship Yamato


Mariko and Jay Clarke[1]

Jacksonville University



Before World War II , Japan had grown from depending on foreign technology and expertise to introducing independently first-rate weapons and innovative doctrines in amphibious operations, surface warfare, and carrier aviation. In 1941 and early 1942, Japan’s mastery of these innovative weapons and ways of war—including unique tactics built on long-range guns and torpedoes, and night combat—gave the Empire a marked advantage over its rivals.

To understand Japan’s growing abilities, between the two world wars the U.S. Navy created a cadre of Japanese-speaking, militarily savvy junior officers, and more than half of the eleven U.S. naval attachés who served in Tokyo were captains.  For its part, the Office of Naval Intelligence (ONI) employed officers who had lived and studied in Japan. These intelligence personnel monitored the Japanese navy’s order of battle and doctrine, but evaluating concepts not yet proven in combat challenged them. One U.S. naval attaché in Tokyo, nonetheless, naively suggested that about 95 percent of the information he sought was available in open sources.[2]

Misplaced optimism. One pertinent story between 1936 and 1941 was how much—and how little—the United States divined about the 18.1-inch gunned, 73,000-ton leviathans, the battleships Yamato and Musashi, the Japanese built and commissioned as war broke out in the Pacific. As early as January 1936, as Japan was withdrawing from the London Naval Conference and the world was preparing for the imminent expiration of the Washington and London naval treaties, rumors began circulating that Japan was building super dreadnoughts. These new, 45,000-ton vessels supposedly would carry 16- or 18-inch guns,[3] but U.S. intelligence consistently downplayed reports of the larger guns.

Willfully blind, only after war’s end did ONI nail down how formidable the Yamato and Musashi had been. One postwar analysis at the Naval War College showed that the war-time assumptions that the two Japanese battleships carried 16-inch guns meant that America’s capital ships would have chosen to fight at a range favoring the Yamato: “[I]nstead of being superior, the [Iowa-class] New Jersey would have been inferior to Yamato.” By “shell-weight and penetration; and the ‘range band’ where New Jersey is shown superior on the diagram, is . . . the band she should avoid.”[4] Other analysts have been more generous in their estimates of American chances: “Without question the Iowa-class battleships were the best ever built. They possessed an unmatched combination of great offensive power, good protection, and high speed.  Ships of other nations occasionally equaled or surpassed them in specific categories, but no other capital ships ever built had such an impressively balanced combination of military characteristics.”[5]

Incited by these contradictory opinions, since the war naval thinkers and military gamers have romanticized a mythical ship-to-ship battle pitting the Yamato’s 18-inch guns against the 16-inch guns of American’s Iowa-class battleships. America’s military planners before and during World War II, however, had to respond to Japanese construction based on a profound underestimation of Japanese designs and capabilities.


The Pre-War Fog

The Italo-Ethiopian War of 1935 and 1936 began the process of grouping the alliances that fought in World War II. More immediately, the war had consequences in the Western Pacific where, distracted by the Italian challenge in the Mediterranean, Britain’s Royal Navy could no longer be counted on to sufficiently challenge Japan.

The United States picked up the cudgel. The preliminary negotiations held in London in 1934 to prepare for renewing the Washington Disarmament Treaty had already illuminated the incompatibility of American desires for “equality of security” against Japanese wishes for parity in tonnage of naval vessels. By September 1935, President Franklin Roosevelt’s order making the western end of the Aleutian Islands the first of a series of powerful air bases in the Pacific further clarified the conflicting policies cleaving the United States and Japan.[6]

America’s naval attaché reported that Japan’s naval minister had secretly told the Diet in May 1936 that Japan wished to have a fleet as strong as any that could be formed in the Western Pacific to attack Japan. Implicitly recognizing Japan’s inability to match America’s productive capacity, the minister continued,


[E]qual strength … does not mean having a numerically equal force, ship for ship.  As a result of the coming no-treaty period we shall enjoy freedom of action in construction of warships in respect to category, quality and characteristics. With this freedom we may construct those ships particularly adapted for our national requirements, thereby gaining an advantage which obviates the necessity for numerical equality.[7]


In other words, the Japanese with fewer big ships hoped to overcome a greater number of U.S. and British vessels. To compete successfully with Japan, the United States would have to build ships too large to pass through the Panama Canal. The Americans would have to build two separate fleets, thereby halving the potential force Japan might have to face.[8]

The Japanese, of course, designed their official, public pronouncements on battleship construction to obfuscate. Unfortunately, too many reports of America’s attachés in Tokyo reflected Japan’s effort to minimize the importance of its building program. In May 1937, one swallowed Japan’s naval minister’s assertion that Japan did not contemplate an armaments program “that might menace other countries.” Further, the minister denied as “sheer speculation with no foundation” that Japan proposed to build huge ships with guns larger than sixteen inches.  The attaché commented:


This is the first definite announcement by the Navy department of the size and gun calibers of the two capital ships Japan is believed to be laying down. While it is of a negative nature, the Navy Department goes on record as denying current press reports of huge ships carrying guns larger than 16 inches. The opinion is gaining ground in Tokyo that Japan does not contemplate construction of capital ships of a size greatly in excess of present types nor mounting guns larger than those now installed.[9]


He did note, however, that the frustrating limits imposed on visits to Kure, Kobe, and Yokosuka had led him to believe that important naval construction was either under way or contemplated at those places.[10]

The view from Tokyo was never clear, and not everyone among their colleagues stationed in Tokyo agreed with the Americans’ more sanguine understanding of Japanese naval construction. One foreign officer claimed to have reliable information that Japan was building 50,000-ton capital ships mounting 18-inch guns.[11] Other foreign attachés were insisting that Japan would not adopt the 14-inch gun. The American attaché agreed, although he admitted that he had “no direct information” on the subject. The British ambassador had information that the Japanese were testing not only 16- but also 18-inch guns. Some were speculating that Japan might build a 50,000-ton ship “on the theory that the present type might thus be tendered obsolete and qualitative parity would result therefrom.”[12] Japan even kept its allies, Germany and Italy, in the dark.  Meanwhile, public Japanese sources stressed Japan’s need for an aggressive building program.[13]

Amid Japanese secrecy on their naval construction, America’s attaché in 1938 described the problems he and his colleagues faced:


Japan’s present building program is based upon surmise as to the meaning of the many statements made by high Naval authorities, estimates of Japan’s requirements and conjecture as to the probable types to fulfill those needs. Undoubtedly, there have been leaks in the form of unguarded statements now and then from officers of lower rank and, possibly, information has been supplied by the Japanese Naval authorities to representatives of the two countries now allied with Japan.[14]


As the world girded for the approaching world war, America’s attachés read the tea leaves on Japanese naval building as best they could.[15] The U.S. Navy widely circulated their estimates and in 1940 reported them to the Senate Naval Affairs Committee as “reasonably certain.” ONI listed with a “small margin of error” eight battleships, each armed with twelve, 16-inch guns as a conservative figure. The Naval War College saw the Japanese program as less threatening. In June, 1940, officers at Newport placed on the game board only four modern enemy battleships, each with nine, 16-inch guns.[16]

Among his last reports before Japan’s attack on Pearl Harbor on December 7, 1941, the United States attaché concluded that the Japanese had at last completed their eleventh battleship.  Tentatively identified as the Kii, they had cloaked her in extraordinary secrecy. Laid down at Sasebo in October, 1937 and launched two years later, the battleship then went to Kure for fitting out and underwent trials in August 1941. Commissioned in October, she weighed in at 35,000 tons, mounted nine 16-inch guns in three triple turrets, and could reach 28 knots.[17] He was writing about the Yamato.


The Fog of War

American intelligence between 1941 and 1945 tenaciously clung to its pre-war underestimates of Japan’s capital ship construction. It persistently ignored significant evidence contradicting its prejudices, especially on battleship tonnage and the size of main batteries.

A document of January, 1942 summarized this pre-war conception. It pointed out that the Japanese had neither completed nor commissioned any battleships since 1921 except for the Kii [Yamato]. Over the previous four years, remarkably conflicting reports of new construction had emerged. In 1939, the naval attaché had reported his belief that Japan’s Replenishment Program had provided for building eight new battleships ranging in displacement from 35,000 to 45,000 tons. It had become increasingly obvious that the Japanese were effectively keeping secret the details of their building program. It appeared, however, that a lack of essential materials had delayed this original program. British intelligence had stressed the possibility that Japan was building four battleships of which one or two displaced not more than 42,000 tons.  The others displaced about 35,000 tons.[18]

After December 7, America’s sources of information on the Yamato changed dramatically. Analyses of aerial photography, prisoner-of-war interrogations, radio traffic routings, and decoded and translated radio intercepts, after a tenuous start, ultimately pieced together most of Yamato’s operational story. ONI, however, did not completely pierce the Japanese veil of secrecy. Only after war’s end did the United States finally understand the size of the potential threat embodied in the Yamato.

Soon after the war in Europe had begun, Edward J. Mathews put together a team of draftsmen, architects, and others having “some technical knowledge and capacity of third dimensional visualization.” This group set about pulling together the vast body of data available on Japan’s naval and merchant ships, organizing it, and processing it for distribution. Its goal was to put at the Navy’s disposal basic drawings, performance data, and general information on the appearance and technical capabilities of every Japanese ship of military value. For major ships, the group developed and constantly revised master drawings. The group kept reference drawings and data covering standard equipment—guns, mounts, range finders, cranes, davits, boats, torpedo tubes, and torpedoes, and more—to help uncover the size and capacity of unfamiliar ships.[19] The group knew that the Japanese were building huge ships in secret as the war began.  The Americans understood little more of their size, although they thought that two of them bore the names Yamato and Musashi.

The first information that came from the field proved disappointing. A Burmese in the British service managed to sneak into one of the protected enclaves to make some drawings. The Japanese caught the spy, and Mathews found the information of little use: “And it is sad to report that to him the new battleships looked for all the world like Burmese junks and the drawings provided no worthwhile data whatever!”[20]

In coming to understand the potential of the Japanese Navy, prisoner of war interrogations were crucial. Compared with other theaters of war, in the Pacific American forces did not capture large numbers of military men. Those Japanese who did fall into American hands, however, provided significant military intelligence, including information on the Yamato.  Unfortunately, American intelligence too often ignored what they were hearing, especially when it challenged their preconceptions of Japanese abilities. Following the Battle of Midway in early June 1942, for example, the American submarine Trout picked up two survivors from the cruiser Mikuma. They stated that the latest battleship in Japan’s Navy, the Yamato, flew the flag of the Commander-in-Chief of the Combined Fleet, displaced 57,000 tons, and could reach a rumored speed of 30 knots. American intelligence dismissively refused to accept these statements without further confirmation.[21]

In August, America launched its first major move after its victory at Midway. U.S. marines took the little island of Tulagi, just off Guadalcanal Island. Caught “flatfooted,” the Japanese garrison “took to the bush.” After the battle, a marine intelligence officer came across a scrap of paper with a crude drawing of a ship.  On the other side of camp, the Americans found a copy of a letter in a dump. It bore a multiple address to Pacific commands and read, in effect, “Here is a drawing of the Yamato to be used for recognition purposes.” The intelligence officer separated these two documents “from the immense mass of junk.”[22] This information reached Mathews’ group a couple of weeks later. The sketch looked like nothing they had ever seen.  From the main batteries and other details, the group concluded that the drawing was not of any known Japanese capital ship but rather represented one of the Yamatos.[23]

An ONI report in October 1942 estimated Yamato’s size at 35,000 tons and her main armament as nine, 16-inch guns. For security reasons, the Japanese termed the ammunition for these guns as “special type 40 cm,” deceiving ONI into believing that the 16-inch estimate was accurate. Naval Intelligence had a hard time budging from this estimate.[24]

On January 13, 1943, in a long report intelligence tried to describe the extent of Japanese naval construction. The report began with the obligatory, “The secrecy with which new construction for Japanese navy is shrouded us well known, and therefore it has been found virtually impossible to disseminate accurate figures on this vital subject.” ONI, nonetheless, suggested it had a decent handle on major ships. The Japanese had completed two new battleships, the Yamato and Musashi, since the outbreak of hostilities.

In early 1943, several POWs reported on the Yamato’s deployment. Most importantly, two New Zealand antisubmarine corvettes on January 29 sank the I-1, a Japanese submarine that was carrying supplies from Rabaul to Guadalcanal. One of the survivors reported that the Yamato had been completed, and he boasted that a new battleship he had seen under construction would be bigger and better than was the North Carolina. Another claimed that he had seen the Yamato at Yokosuka in March, 1942. He estimated that the ship carried a main battery of nine 45-cm guns in three triple turrets. Intelligence officers concluded that, if the POW was correct, the Yamato probably had the most powerful main battery afloat. Documents recovered from the I-1 also provided a windfall for the Americans.[25]

In July, 1943, the Americans intercepted a message from Tokyo to its naval attaché in Berlin. Responding to the Adolf Hitler’s “special request,” Tokyo had decided to allow Germany’s attaché in Tokyo to inspect the Yamato. The Japanese insisted on the strictest secrecy for the inspection, and because they did not want anything leaked to the Italians, they wanted their attaché in Berlin to see that the Germans exercised due caution. The German attaché was to see privately only the nominal specifications, which differed from the true figures. In fact, only a small circle in the Japanese Navy knew even the nominal specifications while “nothing” was “known to the German and Italian attachés.”  If Hitler wished to know more, the Japanese would send an officer who would speak with the Germans.[26]


Yamato’s Nominal Specifications Reported to Berlin[27]


235 meters


31.5 meters


9.15 meters

Standard displacement

42,000 tons

Maximum speed

25 knots

Main armament

9 x 40 centimeter guns

Secondary armament

12 x 15.5 centimeter guns

A/A armament (not exceeding?)

12 x 12.7 centimeter guns


4 developing 90,000 horsepower



Keel laid down

November 1937


December 1941


In October, 1943, the Americans intercepted a message sent from Berlin to the German naval attaché in Tokyo. Apparently, the Japanese were now only slightly more forthcoming with their ally. The Germans were asking technical questions, especially about Yamato’s side and horizontal protection systems. While the Japanese in Berlin were answering all questions as best they could, the Nazi government felt that Tokyo officials had held back valuable information. The German attaché was to send the requested drawings and descriptions as quickly as possible—even in Japanese script, as there were satisfactory translators in Berlin. The Germans wanted to know the degree of Japan’s willingness to cooperate.[28]

The Americans held one significant advantage over the Germans in uncovering the Yamato’s true characteristics—they had access to prisoner of war information. In early July, 1943, one POW described the Yamato as 900 feet long, with three, three-gun main batteries. The guns were between 45 and 48 cm. The ship displaced about 50,000 tons and could reach rumored speeds of 25 to 35 knots. He believed the most likely speed was 28 knots.[29] Another POW who had seen both the Yamato and the Musashi stated in mid-July that the two were identical. He added that the small craft housed in mysterious tunnels on the sides of the battleships were either submarines or motorboats.[30]

Into the autumn, American intelligence continued having hard time recognizing the full implications of the reports they were receiving from prisoners on the Yamato and Musashi. The two ships displaced, intelligence officers thought, 45,000 tons, “although less reliable sources” had given “the figures of 50,000 and 57,000 tons.” The class could reach 28 knots and carried three planes. “According to the best information, the main batteries consist of nine 16” guns, arranged in 3 triple turrets.” However, “[c]ertain Japanese sources [that is, POWs] gave the diameter of the guns as 45 cm, or 17.7”, but the figure is believed to be exaggerated.”[31]

The Americans always had a better grasp of Yamato’s operational record, and they well-understood that Japanese logistics were so stretched by late 1943 that they had to resort to using their major capital ships, including the Yamato, as supply vessels.[32]

Meanwhile, Allied intelligence was using its mastery over Japanese codes to set up submarine attacks. During November and December, for example, major vessels of the Imperial Navy suffered at least six torpedo attacks. Even the Yamato was not immune. As early as December 13, the Americans knew that the Yamato was to arrive at Truk on the twenty-fifth ferrying men and material. On Christmas Day, and 180 nautical miles north of Truk, the USS Skate struck the Yamato on the starboard quarter. This was Yamato’s first real contact with her American enemy. At 0518, it had been too dark for the Skate to know what she had hit other than a large warship. The Americans began to uncover the target’s significance only after intercepting several radio communications from the Yamato describing her damage. Still capable of making 20 knots, the Yamato was to leave Truk on January 10 and arrive on January 15 for dry-docking at Kure. Her damage repaired, the Yamato was quickly back at Truk.[33]

Soon the Americans had more information on the Yamato in the form of “the fuzziest, most distorted aerial photographs” with which Mathews’ group ever had to work.[34] On February 4, 1944, two U.S. Marine B-24 bombers flew over Truk. Photographs revealed the volcanic basin full of heavy cruisers, odd naval vessels, and a “large amorphous blob,” out of center and focus, and at first taken as an island. Stereo viewers, however, revealed a vessel unlike any known to the Americans. With the distortion, uncovering accurate dimensions seemed impossible. The photographs then went to the photo interpretation center in Anacostia. One week later, the resulting drawings closely resembled the earlier Tulagi ones. They suggested astonishing dimensions: a length of 950 feet; a beam of 110 feet; a main battery of nine 18-inch/50 caliber guns, and a powerful secondary battery of 8- and 5-inch guns.[35]

The photos over Truk stirred debate among analysts. On February 25, they were also processed at Pearl Harbor. ONI brought ship-design experts into the discussion, and they concluded that the Yamato-class displaced at least 60,000 tons. That also was the size experts thought necessary to mount 18-inch guns, but these same people argued that problems of stowage and propulsion, plus complications with docking and navigation, would render such a warship impractical.[36]

Prisoner of war information again supplemented photographic evidence. One ONI report recognized that the Yamato and Musashi had long been mystery ships, even to Japanese personnel. For security reasons, the Japanese were publishing official documents with false figures on characteristics and capabilities. Nonetheless, with the help of “an intelligent prisoner …believed to be fairly reliable,” ONI produced a sketch. The prisoner, who had served aboard the Yamato and Musashi for a total of thirteen months, claimed that the ships were almost identical. On the controversial subject of main batteries, the POW confirmed the reported triple mounts, but insisted the guns were 45 cm rather than the smaller 40 cm. He claimed that projectiles for these guns stood six feet high, compared with the Nagato’s projectiles, which stood at only 5’6”. Ammunition ordered for the Yamato and Musashi was “40 cm, Type 2” rather than “40 cm, Type 1”. According to the POW, this indicated 45-cm ammunition. The prisoner added that chief petty officers aboard the Yamato often joked that these guns were “the largest 40 cm guns in the Japanese Navy.” Also controversial were the tunnel-shaped compartments on either side of the stern. Did they house submarines or PT boats? The prisoner explained that each tunnel was designed for two midget subs. He added that he had never heard of these subs being stowed there, and that he had no idea how they would be launched. The prisoner saw the compartments used for storage—“including CinC Combined beer.” The hangar was large enough for eight planes with wings folded, but he had seen no more than three carried.  The Yamato, the prisoner said, was of 55,000 tons and could reach 26.5 knots.[37]

The next contact between a Yamato-class vessel and the Americans quickly came. Major Japanese units steamed out of Palau on March 29, 1944, among them the Musashi. Through radio intercepts, the Americans had long known her general location and responsibilities.[38] As the Musashi left Palau, the battleship encountered the submarine Tunny, which launched a six-torpedo spread at the battleship. The Musashi turned to avoid but took a hit in the bow, one that would confine her to the Kure dry dock for slightly more than two weeks.[39]

In April, 1944, a captured Japanese document revealed the official statistics on the Musashi and Yamato—figures similar to those earlier released to the Germans. Despite radio intercepts, including those revealing Japanese efforts to mislead their German allies with figures purposely underestimating the Yamato’s true power, ONI persistently put more faith in these official documents than it did in the veracity of captured Japanese personnel.[40]

Official Characteristics of the Musashi and Yamato[41]








235 meters

235 meters


31.5 meters

31.5 meters


9.15 meters

9.15 meters

Tonnage (standard)




25 knots

25 knots




Built in

Mitsubishi at Nagasaki

Kure Navy Yard

Keel Laid

Mar. 29, 1938

Nov. 4, 1937


Nov. 1, 1940

Aug. 8, 1940


Aug. 5, 1942

Dec. 16, 1941

Main Battery

9- 40 cm

9- 40 cm

2nd Battery

12- 15.5 cm

12- 15.5 cm

A/A Battery

12- 12.7 cm

12- 12.7 cm

Torpedo Tubes







(Same as BB-Haruna?)

(Same as BB-Haruna?)








(Same as BB-Haruna?)

(Same as BB-Haruna?)





Information continued to flow in that ought to have disabused the Americans of those misperceptions. In September, 1944, interrogations of Natori prisoners revealed that it was common knowledge in naval circles that the real dimensions of the Yamato and Musashi were so secret that even official documents used only nominal figures. One POW had seen their main armament listed in documents as 40 cm, but he and his colleagues understood that it was actually 45 cm or possibly even more. The ships, he said, displaced at least 50,000 tons, and he estimated that their maximum speed was 27 or 28 knots.[42] Of course, not all POW information was helpful.  One prisoner claimed that Japan had completed ten new battleships and cruisers in 1943. He insisted that they could reach 47 knots, including the two whose names he knew—the Yamato and Asai.[43]

Interrogations of Japanese survivors, radio intercepts, and captured diaries uncovered that Japan’s naval forces as the First Diversion Attack Force on October 19 had left the Singapore area bound for Leyte to repel an attacking American invasion force. The Japanese, including the Yamato and Musashi, arrived at Brunei Bay and refueled on October 21. The Americans clashed with this imposing force in the Battle of Surigao Straits of October 24 through 26 and repeatedly hit the Musashi and her consorts. The Musashi alone absorbed an astonishing nineteen torpedoes and seventeen bombs. A survivor of the destroyer Kiyoshimo described the last moments of that mighty warship. The crippled Musashi had made her way to near Mindoro, where she was to be taken in tow; thirty minutes after the destroyers arrived, however, the Musashi’s magazines exploded and she sank. The POW said the Japanese people would “shed tears” if they heard of Musashi’s sinking. In his report, the interrogator commented—”Believe her sinking can be announced by us without prejudice.”[44]

The Battle of Surigao Straits was an overwhelming American victory. Of the original thirty-five Japanese ships, only fourteen or fifteen remained afloat. According to intercepted radio reports, Japan’s other dreadnought, the Yamato, had received minor damage from two bombs hits on the deck forward and three torpedoes hits forward on the port side. Causalities included more than fifty killed and one hundred wounded. On October 28, the battered fleet arrived at Brunei, Borneo for temporary repairs, as there were no shipyards.  It stayed there about a month awaiting further orders.  About November 18, the Yamato and others fueled and left for Japan.[45]


The Fog of War Lifts: The End of the Yamato

By piecing together information divined from the levels and routings of radio traffic plus decoded and translated radio messages, ONI had kept reasonably abreast of the Yamato’s activities—despite early confusion between the battleship Yamato and a 4,379-ton merchant vessel of the same name.[46] As the war progressed, prisoner of war interrogations, action reports, and aerial sightings supplemented radio intercept information, and the American estimates got more exact. In the war’s early stages, American intelligence could figure out where the Yamato had been and what she had done. Later, the Americans could grasp where the Yamato was and what she was doing. By the end, they knew where the Yamato would be, how she would get there, and what she was to do once there. Compare the radio intercepts of April through June, 1942 surrounding the Battle of Midway, with those of mid-July, 1943 and later when American intelligence knew when the Yamato and its screening vessels would leave Kure carrying supplies to Truk. Not only did the Americans know what the Yamato would carry but even what anchorage the Yamato would be assigned once at Truk. By December, 1943 when the Yamato returned to Yokosuka, U.S. intelligence knew the exact times, precise distances from fixed navigational points, and exact bearings the Yamato would take to enter the harbor.[47]

The Yamato’s final sortie provides the most dramatic example of the accuracy of the Americans’ knowledge. By early April, 1945, it was clear that the commander of the “First Diversion Attack Force” was likely in the Kure area and aboard the Yamato. On April 4 the Americans had an inkling that this force would sortie with aerial forces against American ships moving on Okinawa. The next day, the Americans knew that the Japanese battle group, also called the “Special Suicide Attack Unit,” would take on 20,000 tons of fuel at Tokuyama on the morning of the sixth. The fleet would then arrive at an area east of Okinawa at dawn on the eighth. The Japanese assigned radio frequencies to the First Diversion Attack Force and informed other naval and air units of its future movements—movements precisely set to prevent friendly attacks. Simultaneously, of course, the Japanese were inadvertently also telling the Americans. The Yamato and her companions were to sortie from Bungo Channel on April 6.[48]

Armed with such accurate information, U.S. planes sighted the Japanese force late in the evening of April 6 in the waters near Kyushu. U.S. Navy Task Force 58 had all the advantages and at 1015 on April 7 launched 380 planes to strike the Japanese force. Guided by a tracking plane, the Americans were able to apply overwhelming force against the doomed Yamato. First reports from the attacking planes, which faced stiff antiaircraft fire but no covering planes, said that the Yamato, still identified at 42,000 tons, took a minimum of eight torpedoes and eight, half-ton bomb hits.  The planes also left other ships badly burning. The Americans took losses of only seven aircraft.[49]

Intercepts of Japanese radio reports confirmed the day’s devastation. One of April 7 reported that about 300 American fighters, bombers, and torpedo planes had attacked the First Diversion Attack from 1230 to 1430. They had sunk the Yamato and other vessels; still others were unable to proceed. A message from one destroyer described the final torpedo attack on the Yamato and her explosion and sinking. Other Japanese radio messages estimated that the Americans had attacked with more than 2000 planes. They also reported that apart from two destroyers, the enemy had either sunk or badly damaged all ships of the Special Suicide Attack Unit.[50]

According to another radio intercept on April 7, Japanese ships had picked up about 600 survivors from the Yamato. On April 8, Japanese planes were to search for the missing ships in an 80-mile radius and then return to Sasebo. That same day, the Surface Suicide Unit radioed its action summary and reported that they had shot down nineteen enemy aircraft. Poorly informed of the battle’s results, Japanese radio operators on April 8 and 9 were still trying to contact the Yamato.[51]

One American report, after analyzing the events of April 7, concluded that the losses sustained by the Japanese had significantly reduced the naval threat to America’s advance on Japan’s homeland. Only on August 29 did the Japanese delete the Yamato from their Wartime Organization charts.  Two days later, they deleted the Musashi and Yamato from the Man-of-War Register. Even at this late date, the Americans continued to believe that the Yamato was only 45,000.[52]


The Fog Lifted: The Post-War Postmortem

Given that the science of warship design in the Japanese Navy dated only from 1918, the boldness of the Yamato’s design was impressive. After the war, ONI devoted considerable attention to her design and wartime performance, gathering documents and interviewing Japanese naval men.[53] This was doubtless interesting and useful information, but it was also akin to closing the barn door after the horse had escaped.

Between the two wars, U.S. naval intelligence had particularly targeted the Japanese navy. In 1938 and 1939, Japanese naval codes and ciphers consumed all of the Navy’s cryptanalysis and 90 percent of its translation efforts. Even so, the Navy was able to read only about 10 percent of the Japanese navy’s coded traffic, mostly material encrypted in eight to ten minor cipher systems dealing with personnel, engineering, administration, weather, and fleet exercises. The Navy could read the main Japanese naval code, JN-25, only intermittently and was unable to read the flag officer’s code. Even so, the U.S. Navy had learned much about Japanese naval strategy from communications intercepted during fleet exercises.[54]

ONI, however, only partly understood Japanese naval tactics. Between American racial and cultural prejudices as well as Japanese secrecy, U.S. Naval Intelligence only belatedly came to grips with Japan’s new approach to naval warfare. The Japanese Navy believed that it needed to defeat the U.S. fleet in a decisive battle to win the war at sea. America’s quantitative superiority had forced Japan to seek ways to offset the U.S. advantage. The Japanese naval staff believed that its ability to defeat the U.S. rested on ships that could outrange their American counterparts, striking U.S. ships beyond their ability to return fire. The Japanese navy therefore expended great effort to increase the range and accuracy of its gunfire. The Yamato-class battleships were the fruit of those efforts.[55]

The battleship had been the centerpiece of both American and Japanese naval thinking between the wars, and ONI had devoted great attention to tracking Japan’s battleship program.  Throughout the 1920s and early 1930s, U.S. intelligence did reasonably well at watching Japanese naval technology.  Despite Japan’s secrecy, the U.S. Navy gleaned considerable data on Japanese naval construction—including accurate figures on the dimensions, tonnage, speed, and armament of Japanese warships—from public as well as foreign sources. Periodic visits to shipyards and naval bases before 1939 allowed attachés to gather insights on Japanese naval construction. U.S. officers gathered what turned out to be accurate intelligence on new weapons systems—the Type 93 torpedo, the Zero fighter, landing craft, and the speed and weight of modernized battleships—only to have the Navy disregard it. The Navy’s experts repeatedly dismissed accurate information showing the Japanese had mastered innovative technologies the United States lacked—reflecting the widespread assumption that Japan had to be inferior to the United States in naval technology. It was also the result of the Navy’s inability to verify empirically the claims made in intelligence reports. Japanese secrecy and rapid technological development considerably degraded the U.S. Navy’s ability to track Japanese naval technology before World War II. The failure to understand novel technological developments held dire consequences when the American and Japanese navies met in combat, especially early in the war.[56]

Not only did US analysts impose their preconceptions on the Japan’s navy and underestimate Japanese technological innovations, the Americans also underestimated their tactical innovations designed to use their new weapons systems. The U.S. Navy mistakenly assumed that Japanese tactics mirrored U.S. tactics.[57]

Scholarly and popular books and articles, websites, board and computer games, and model builders all testify to continued fascination with the Yamato. Amid great international publicity, her remains were located and examined in 1985 and reexamined more carefully in 1999. The great dreadnought lies in two main parts in some 1000 feet of water. Her bow portion, severed from the rest of the ship near the second, main battery turret, is upright. The amidships and stern section are upside down nearby, with a large hole in the lower starboard side close to the after magazines.

The Yamato, which should have been the greatest battleship ever built, in truth was already obsolete when launched in 1941—fire control radar and especially seaborne aircraft had changed the nature of combat at sea. Yamato’s mystique depends on what might have been, rather than what was. In reality, she had been often reduced to ferrying men and material to threatened points in the Empire. Her grand moment, her last desperate sortie to redeem not just the Yamato herself but the entire concept of big-gun capital ships as the centerpiece of fleet strategy, led only to a valiant but futile death.


[1] This is a condensed version of J. Calvitt Clarke III and Mariko A. Clarke, “Yamato wo meguru Bei-Kaigun no Joho-Katsudo” [Intelligence Activities of the US Navy Concerning the Yamato], Youichi Hirama, ed., Senkan Yamato [Battleship Yamato] (Tokyo: Kodan-sha, 2003), 162-196. The authors would like to thank Lt. Cmdr. Roger Thomas (ret.) of Jacksonville, FL and Dr. Jon Sumida of the University of Maryland for their encouragement and advice.  Any errors, of course, are ours.

[2] Thomas G. Mahnken, Uncovering Ways of War: U.S. Intelligence and Foreign Military Innovation, 1918-1941 (Ithaca, NY: Cornell University Press, 2002), 42-44, 46, 57.

[3] Japan Advertiser, 6 February, 1936.


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[4] Malcolm Muir, Jr., “Rearming in a Vacuum: United States Navy Intelligence and the Japanese Capital Ship Threat, 1936-1945,” The Journal of Military History 54 (October, 1990), 485.

[5] Robert O. Dulin, Jr. and William H. Garzke, Jr., Battleships: United States Battleships in World War II (Annapolis, MD: Naval Institute Press, 1976), 107.

[6] For a good description of the conference, see Arnold J. Toynbee, Survey of International Affairs, 1936 (London: Oxford University Press), 49-116.  For Japanese justifications of its new policy directions, see Japan Advertiser, 9 September; 8 October, 1935.

[7] National Archives, College Park, MD, Record Group [hereafter cited as NARA RG] 38, Records of the Office of the Chief of Naval Operations, M975, Selected Naval Attaché Reports Relating to the World Crisis, 1937-1943, Microfilm, 3 rolls (Washington, DC: National Archives and Records Service, 1974), 1: 20 January, 1938; John Prados, Combined Fleet Decoded (New York, NY: Random House, 1995), 21.

[8] Matsumoto Kitaro, Senkan Yamato, Musashi—Sekkei to Kenzo [Design and Construction of the Yamato and Musashi] (Tokyo: Haga Shoten, 1961), 145-46; Makino Shigeru and Koga Shigekazu, Senkan Musashi Kenzo Kiroku [Record of the Construction of Battleship Musashi] (Tokyo: Atene Shobo, 1994), 15-16; Maema Takanori, Senkan Yamato Tanjo [Birth of Battleship Yamato] 2 vols. (Tokyo: Kodan-sha, 1997), I: 245; David C. Evans and Mark R. Peattie, Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy, 1887-1941 (Annapolis: Naval Institute Press, 1997), 294-95.

[9] NARA RG 38, microfilm, 1: 22 May, 1937.  See Prados, Combined Fleet, 20-21.

[10]NARA RG 38, microfilm, 1: Mar. 16, 17, 1937; 22 May; 26 June; 3 September; 29 October, 1937; Muir, “Rearming in a Vacuum,” 476.

[11] NARA RG 38, microfilm, 1: 22 May, 1937.

[12] Robert H. Levine, The Politics of American Naval Rearmament, 1930-1938 (New York: Garland Publishing, 1988), 419.

[13] NARA RG 38, microfilm, 1: 28 January; 22 May, 1937; 16, 20 January; 18 February, 1938; 14 February, 1939; Muir, “Rearming in a Vacuum,” 476.

[14] NARA RG 38, microfilm, 1: 20 January, 1938; also see Japan Advertiser, 3 April, 1936.

[15] NARA RG 38, microfilm, 1: 28 January; 15 February. 1937; 13 March, 12, 27 April, 1939; NARA RG 38, Box 89: Records of the Chief of Naval Operations. Office of Naval Intelligence Monograph Files. Japan 1939-46:16 January; 14 February; 16 March, 1939; 11 October; 14 March; 1 April; 8 October 8, 1940; 8 May, 1941; Hara Katsuhiro, Senkan Yamato Kenzo Hiroku [Untold Story of the Construction of Battleship Yamato] (Tokyo: KK Best Seller, 1991), 53.

[16] Muir, “Rearming in a Vacuum,” 478.

[17] NARA RG 38, Box 89: November, 1941.

[18] NARA RG 38, Box 89: 6 January: 16 March, 1942.

[19] Edward J. Mathews, “What Ship is That? US Naval Institute Proceedings (July, 1978), 61-62.

[20] Ibid.

[21] NARA RG 38, Box 89: 26 March; 15, 17, 21, 26, 28 June, 1942; n.d.

[22] Mathews, “What Ship,” 64-65.

[23] Ibid.

[24] Prados, Combined Fleet, 415. Among captured documents, Americans found several pages of Life magazine showing pictorially the naval strength of the world’s sea powers. Three new Japanese battleships were sketched: the first two were Yamato and Musashi; the third was unnamed. NARA RG 38, Box 1448: Translations of Intercepted Radio Traffic and Miscellaneous World War II Documentations, 1940-1946, Japanese Orange Translations: 15 October, 1942.

[25] NARA RG 38, Box 1448: 12 February, 1943; 3 March, 1943; RG 38, Box 89: 19 April, 12 May, 1943; Prados, Combined Fleet, 401.

[26] NARA RG 38, Box 1448: 4 July, 1943.

[27] Ibid.

[28] NARA RG 38, Box 1448: 24 October, 1943.

[29] NARA RG 38, Box 1448: 8 July, 1943.

[30] NARA RG 38, Box 1448: 17 July, 1943. For a report summarizing Naval Intelligence’s views of the state of Japanese battleship construction including the Yamato and the Musashi, see NARA RG 38, Box 89:28  July, 1943.

[31] NARA RG 38, Box 1448: 9 September, 1943.

[32] See, e.g., the radio intercepts from July through December in NARA RG 38, Box 1448 regarding the Yamato: 15, 19, 20, 21, 25, 30 July; 2, 3, 6, 12, 23 August; 10 October; 11, 13, 16, 20, 25 December, 1943.

[33] NARA RG 38, Box 1448: 13, 24, 25, 29 December, 1943; January; 9 February, 1944; Prados, Combined Fleet, 533.

[34] Mathews, “What Ship Is That?” 65.

[35] Ibid., 64-65. Muir, “Rearming in a Vacuum,” 481, gives slightly different figures: length, 840 feet; beam, 125 feet; main battery, nine probable 16-inch guns in triple turrets; secondary battery included 8 probable 8-inch guns in twin mounts.

[36] Prados, Combined Fleet, 534-35.

[37] NARA RG 38, Box 89: n.d.

[38] See, e.g., NARA RG 38, Box 1448: 1, 2, 11, 14, 16, 24 March, 1944.

[39] Prados, Combined Fleet, 548.

[40] NARA RG 38, Box 1448: 14 April, 1944; NARA RG 19, Box 467, 15 April, 1944; Prados, Combined Fleet, 534-35.  For captured Italian documents, see NARA RG 38, Box 89: 11 August, 1944.

[41] NARA RG 38, Box 1448:14 April, 1944; NARA RG 19, Box 467, 15 April, 1944.

[42] NARA RG 38, Box 1448: 13, 21 September, 1944.

[43] NARA RG 38, Box 1217: 23 November, 1944.

[44] NARA RG 38, Box 1448, 5, 24 October, 1944.

[45] NARA RG 38, Box 1448: 24, 25, 26, 28 October; 18 November, 1944. Different sources give slightly different figures for the killed and injured on the Yamato.

[46] NARA RG 38, Box 1448: 21 July, 1942.

[47] For this progression, see NARA RG 38, Box 1418.

[48] NARA RG 38, Box 1448: 5, 6 April, 1945.

[49] NARA RG 38, Box 1448: 7 April, 1945.

[50] NARA RG 38, Box 1448: 8 April, 1945.

[51] NARA RG 38, Box 1448: 7 April; 29, 31 August, 1945.

[52] NARA RG 38, Box 1448: 8, 9 April; 31 August, 1945; n.d.; NARA RG 0019, Box 467: Bureau of Ships. General Correspondence 1940-1945: 24 July, 1945.

[53] See, e.g., NARA RG 38, Box 1448: 6 September; 15, 16, 17, 25 October; 7, 12, 24, 25, November, 1945; NARA RG 38, Box 89: 7 November, 1946.  The results of this information gathering can be seen in NARA RG 38, Box 89: “The Yamato and the Musashi,” 2-17 and “The Yamato’s 18-Inch Guns,” 17-19.

[54] Mahnken, Uncovering Ways of War, 58.

[55] Ibid., 58-59.

[56] Ibid., 62, 64, 66-67, 71.

[57] Ibid., 57, 61-62.