After World War I, the Imperial Japanese Navy concentrated on preparing for a possible confrontation with its most likely adversary, the U.S. Navy. Japanese naval leadership faced two major challenges: The first was the numerical superiority of the U.S. battle line, 14 battleships to Japan's 10; the second was the set of restrictions on warship construction imposed by the international naval arms limitations system which, until 1937, froze this ratio in place.
To compensate, the Japanese Navy turned to tactical innovation and superior warship design. During the 1920s, it worked out an attrition strategy using light forces, including destroyers and cruisers, against the U.S. fleet, which was expected to plow westward through the Pacific in the course of a possible war. A key aspect of this strategy was Japanese emphasis on night torpedo attacks from destroyers and cruisers against U.S. capital ships.
For this purpose, early in the same decade, the Japanese Navy developed the Fubuki-class destroyer. Nearly 400 feet long and displacing close to 2,000 tons, these were enormous ships for their type. But it was their firepower—greater than that of many light cruisers—that was unprecedented: six 5-inch guns in three enclosed mounts and nine 24-inch torpedo tubes mounted in three triple banks. This armament and the general layout above the weatherdeck, including a high bridge, massive gun houses, and tall funnels, added considerable topside weight.
In the latter half of the 1920s the Navy General Staff turned its attention to the development of the cruiser, not just as a scout for the fleet, but as an all-purpose warship fast enough to coordinate destroyer operations and firepower, which would enable it to blast open a path for the destroyer flotillas. The Washington Naval Treaty of 1922 had placed quantitative limits on cruiser design—no displacement of more than 10,000 tons and no guns greater then 8 inches in caliber—but not on the aggregate tonnage in cruisers that each signatory nation could build. Because of a total ban on battleship construction, a naval race in cruisers, the next-largest category of warship, was inevitable. Thus was born the "treaty cruiser," favored particularly by the Japanese and U.S. navies.
The Japanese had begun the competition with a cruiser design that combined heavy armament and high speed within a hull of modest proportions. Drawn up by the their navy's most well-known naval architect, Captain Hiraga Yuzuru, and his assistant, Lieutenant Commander Fujimoto Kikuo (Japanese names are given family name first), the first two of what were later dubbed "A"-class or heavy cruisers carried 12 24-inch torpedo tubes, in addition to their 6 8-inch guns. The Navy General Staff insisted on this unusually heavy torpedo armament over the vigorous objections of Hiraga, who believed that the excessive firepower risked the stability and integrity of these ships. Later cruisers extended this principle.
The construction of the four cruisers of the Myoko class is a case in point. The initial staff requirements for the class included armament for ten 8-inch guns in five turrets, eight torpedo tubes, and armor for protection against hits by 15-cm shells. While Hiraga accepted most of these requirements, he balked at the plan to install fixed torpedo mounts below decks as dangerous and unnecessary. But in 1925, during Hiraga's absence in Europe, torpedo specialists on the General Staff prevailed upon Hiraga's temporary successor, Commander Fujimoto, to install 12 fixed torpedo tubes. By loading these ships to comply with the tactical demands of the Navy General Staff, Fujimoto allowed them to be heavier than planned (or permitted by treaty limits) by about 1,000 tons. Thus, the Japanese bought their firepower at the price of inadequate seaworthiness, stability, and longitudinal strength.
Hiraga was still in Europe when the four cruisers of the Takao class began to appear on the drawing boards. Responsibility for their design lay with Commander Fujimoto, who was far more susceptible to pressure from the General Staff than Hiraga. Since the Takaos were to function as fleet flagships in time of peace and as division flagships in wartime, the staff required that their design incorporate command centers to coordinate both day and night battles involving long-range gunnery and torpedo attacks. This further contributed to their topside weight by adding communications, command, navigation, and fire- and damage-control stations, all grouped together in an enormous bridge. They thus achieved centralization of command functions but at a perilous cost.
In 1930, the representatives of the world's great naval powers met again in London to review and extend the naval limitations agreed upon eight years before. One proposal called for a cruiser tonnage ceiling. To the fury of the Navy General Staff, the Japanese Navy was forced to accept not just an inferior ratio across the board, but an actual reduction in strength in relation to the other two major naval powers, Britain and the United States. Japan was thus obliged to halt further construction of heavy cruisers—a category in which, during the previous decade, it had labored with such effort to seize a lead. The London Treaty was the last straw for the Japanese Navy's mounting frustration with the naval limitations system, but in 1930 Japan found itself in the position of having to wait six years before it could break free of the treaty's binds. The Japanese Navy's response, undertaken with considerable skill and ingenuity, was to build to its allotted tonnage limits in each of the restricted warship categories.
Faced with the fact that Japan had built up to its quota in 8-inch gun cruisers, the Navy General Staff, still determined to make cruisers the centerpiece of its night-combat tactics, decided to use its remaining cruiser allocation to build 6-inch gun cruisers capable of slugging it out with 8-inch heavy cruisers. To achieve this, Fujimoto Kikuo (then a captain), who had responsibility for designing the four ships of the new Mogami class, arranged that they should carry 15 6-inch guns in five triple turrets, three forward and two aft, and four triple torpedo mounts in the hull, two on each side. The staff's combat requirements for the class, the same as those for the 10,000-ton "A"-class cruisers, called for armor capable of withstanding 8-inch shells and, most remarkable of all, for gun turrets that could be converted rapidly to accommodate 8-inch ordnance. The displacement of these light, or "B"-class, cruisers was significantly greater than the 8,400 tons called for in the staff's original specifications. When completed, the Mogami class was armored more heavily than any heretofore Japanese light cruiser and had greater firepower—including heavier antiaircraft armament—than any British or U.S. "light" cruisers. Fujimoto had tried to keep the weight down by using light alloys and electric welding wherever possible, but once more, the reckless demands of the General Staff had resulted in a design marked by excessive top-weight and thus by dangerous instability.
A number of Japan's newest cruisers and destroyers also had a problem with longitudinal strength. Depending upon the length and the beam of the particular ship, all modern warships are designed to deal with certain wave configurations. This strength must be adequate to ride the crest of a wave or straddle a trough between two waves.
In designing ships that can traverse the oceans successfully, naval architects routinely assign a numerical value representing the most extreme ratio they expect ships to encounter. The normal waves in Japan's home waters had a gently curving height-breadth ratio of between 1 to 20 and 1 to 30. The Japanese Navy had therefore designed its destroyers, particularly the Fubuki class, to deal with such wave conditions. Obviously, for such ships a different wave configuration and ratio—a steeper, more triangular wave with a height-breadth ratio significantly less than 1 to 20—might create dangerous stresses to the hull. In the case of the Mogami-class cruisers, faulty welding, a flaw discovered during test-firing of the main batteries, compounded the problem.
Thus, it was inevitable that, in certain circumstances of wind and weather, disaster would overtake one of the Japanese Navy's newest ships. Surprisingly, however, when it did so, the warship in question was one of the smaller units.
Having also been limited by the London Treaty to a lower aggregate tonnage in destroyers than it considered necessary, the Japanese Navy decided to fill the gap with a new type of warship, a 600-ton torpedo boat that could guard Japanese ports and naval bases. The first four of the Chidori-class torpedo boats, a projected series of 20 ships, were laid down in 1931 and 1932 and were completed between 1933 and 1934. The navy placed great hope in these small vessels, which were also expected to take over the routine patrol and antisubmarine duties of larger destroyers. But once again, the demands of the Navy General Staff for offensive power resulted in a design that was perilously top-heavy, since they mounted the heaviest possible armament—four 21-inch torpedo tubes and three 4.7inch guns—in a very small hull.
In March 1934, several of the new vessels, including the torpedo boat Tomozuru, were engaged in maneuvers with other fleet units off the west coast of Kyushu. On 11 March, a gale hit the operating area. The sea grew rough, and the smaller craft began to roll, the Tomozuru taking rolls of up to 45. During the night, the gale continued unabated, and the small ships became scattered. Early in the morning of 12 March, the Tomozuru, steaming at a remarkable 14 knots through heavy seas, took a roll from which she never recovered. The light cruiser Tatsuta found her early the next afternoon, drifting keel up, some 50 miles to the southwest, and took her in tow, stern first. When the derelict was righted in Sasebo Harbor, only 13 of the original 6 officers and 107 crew were left alive.
The Tomozuru disaster sent shock waves through the Japanese Navy. In two subsequent official inquiries into the cause of the accident, the fundamental instability of this class of torpedo boats became apparent, and measures were recommended to improve seaworthiness in ships that were still being built. The navy canceled the 16 boats in the program that had not been laid down and abandoned the idea that the four completed boats could replace even second-class destroyers.
Several investigation boards looked into the causes of the accident. Ironically, Admiral Kato Kanji, former Chief of the Navy General Staff, headed the second board, which met April through June 1934. In the end, the scapegoat was Captain Fujimoto, Chief of the Basic Design Section of the Japanese Navy's Technical Department and the General Staff's willing executor, who eventually was sacked and died, a broken man, the following year. Because he had been so heavily involved in the design of so many ships then in service, their stability and integrity were suspect.
But retrofitting a major portion of the Japanese fleet would be expensive, just at a time when the Japanese Navy needed major funding for new construction programs once the era of naval limitations came to an end in 1937. For the moment, the navy did nothing beyond revising the plans for the ships of the Chidori class still to be laid down and undertaking certain measures to increase the stability of those ships from the class already in service. Then, just more than a year after Japan's naval planners had begun to realize the faulty design of a significant portion of their ships, a second calamity at sea reaffirmed the implications of the Tomozuru disaster. And this time it struck not just one ship, but a whole fleet.
In summer 1935 the Combined Fleet, the Japanese Navy's largest single fleet organization, engaged in annual grand maneuvers in the waters southeast of Hokkaido. As the maneuvers entered their final phase, the Combined Fleet organized itself temporarily into a "Blue Fleet." representing a Japanese defending force and comprised of the First and Second fleets, and a "Red Fleet," representing the enemy and composed of the Fourth Fleet. Early in the morning of 25 September, the Fourth Fleet, sortied from its base at Hakodate on southern Hokkaido. The force steamed east, then south, to about 100 nautical miles east of northern Honshu.
Early that morning, Japan's Central Meteorological Observatory warned the Fleet of an approaching typhoon some 150 nautical miles east of the Chiba peninsula, to the south, and moving northward at 43 to 50 miles per hour over a 125-mile front. It was, in fact, one of two typhoons moving northward in late September. The first, born north of Ulithi Atoll in the western Carolines, struck the islands of Shikoku and Honshu from 24 to 25 September, but did not threaten the Fourth Fleet. But the path of No. 2 Typhoon (as it came to be called) lay right across the fleet's course. Born in the waters northeast of Guam, while the Fourth Fleet was still at Hakodate, it had become a powerful storm by the time it reached the Bonins on the 25th. That evening, it was moving north at 28 miles per hour and, within a radius of 60 miles, carried winds of terrific force.
By late morning on the 26th, the barometers began to fall significantly on the main ships of the fleet, and the weather began to turn ominous, with low, scudding clouds and heaving swells. At best it is a challenge to try moving an entire fleet expeditiously out of the path of such weather. For this reason, the fleet commander, Admiral Matsushita Hajime, felt that he had no recourse but to ride out the approaching storm, though he ordered a southward course so that the storm would not hit his fleet broadside. All ships secured for heavy weather.
When the typhoon hit the Fourth Fleet, it was steaming at 10 knots in three principal parallel groups: in the center was the main force of six heavy cruisers, five light cruisers and a submarine tender, plus a carrier division of two carriers with an escort of four destroyers; some 100 nautical miles east of the main body were ten destroyers of four destroyer squadrons, led by a light cruiser; and about 110 nautical miles to the west of the main force were 11 submarines of four submarine squadrons led by a light cruiser. A navy oiler struggled along by itself between the main force and the destroyer division.
By early afternoon of the 26th, as the main body neared the eye of the storm, the waves had become truly threatening. Winds had reached more than 45 miles per hour and soon were up to 90. After it entered the eye early in the afternoon, the wind died down, but the ocean was still in turmoil, and waves some 50 to 60 feet high struck the ships of the main force. Reentering the storm by mid-afternoon, this central group encountered wind speeds of nearly 70 miles per hour. The flight deck of the Hosho was distorted and the bridge smashed, and the bridge of the Ryujo was caved in. The accompanying ships suffered less visual damage—but it was real, nevertheless.
Some 100 nautical miles east of the typhoon's eye, the smaller ships, particularly the destroyers, were receiving far worse punishment. By early afternoon, the winds had reached 122 miles per hour, and waves of 50 feet or more were smashing against the bridges of the small ships. The bridge windows of the destroyer Yugiri were shattered, as were those of the Yuzuki, Mikazuki, Harukaze, Hokaze, and Kikuzuki. On the destroyers Asakaze and Mochizuki the waves did structural damage to the bridge itself, and on the Mutsuki the bridge was actually crushed.
The light cruiser Kinu took a roll of 36°, but the rolls of some of the destroyers—up to 75°—were truly terrifying. That none capsized is testimony to a certain amount of good shiphandling but probably far more to extraordinary luck. Neither luck nor shiphandling, however, could ease the enormous strain on hull structures caused by the mountainous seas. Just after 1600, some 250 nautical miles east of the port of Miyako, the bow of the Yugiri broke off and disappeared under the waves, carrying with it the men trapped in the forward part of the ship. About an hour-and-a-half later, more men were lost when the bow of the Hatsuyuki also broke off just in front of the bridge as she tried to crest a huge wave. With watertight doors secured on both ships, they were able to stay afloat.
By nightfall of the 26th, the worst of the storm had passed, and other ships in the squadrons took the mutilated Yugiri and Hatsuyuki in tow, stern first. On 2 October, the battered fleet began making its way back to port. Casualties numbered 54 officers and crew drowned, fatally injured, or missing.
In the immediate aftermath of the disaster, the Japanese Navy established an investigation commission, which concluded that basic designs and limitations had contributed substantially to the damage, which was compounded by faulty welding. It also addressed the problem of instability and called for reducing excess topside weight and raising the metacentric height of the ships.
With the evidence of the Tomozuru and the Fourth Fleet disasters manifest, the Japanese Navy delayed by several years some major construction, while it undertook a huge program of modification.
First, torpedo boats and destroyers were significantly redesigned and reconstructed. The design of the four boats of the Chidori class, completed or building, was modified drastically by scaling back the size and protection of the main batteries, by reducing the number of torpedo mounts and torpedoes carried on deck, by lowering the bridge one deck level, and by adding keel ballast. The eight torpedo boats of the succeeding Otori class, building or completed, incorporated all the lessons learned from the capsizing of the Tomozuru. The 16 destroyers of the new Hatsuharu and Shiratsuyu classes were modified extensively: the upper works were more compact and efficient, the guns were repositioned, one torpedo mount was removed, extra ballast was added, and extra equipage from the main deck was removed.
But the cruisers, particularly those of the most recent Mogami class, caused the greatest concern. In autumn 1936 the Mogami and the Mikuma were placed in reserve and sent for partial reconstruction to the Kure Naval Yard to improve their transverse stability. The enormous bridge on these ships was lowered, the deck heights were reduced, and extra bulges were added to the hull. These modifications were incorporated into their sister ships, the Kumano and the Suzuya, which were still building. The Takao-class ships were also placed temporarily in reserve in late 1935 at Yokosuka Naval Base to improve longitudinal strength.
The lessons of the Tomozuru and Fourth Fleet "incidents" (as the Japanese referred to them) also influenced the design of the two new Tone-class scout cruisers. These ships were improved versions of the Mogami class, being far more stable (partly owing to the addition of side armor and underwater bulges) and employing a radical arrangement for their main armament—eight 20-cm guns in four turrets—all being sited forward of the bridge that left space aft, free from gun blast, for five reconnaissance aircraft and two catapults to launch them. Whatever the tactical concept behind their design, for stability, seaworthiness, and speed, they proved to be excellent ships.
The No. 2 Typhoon taught one other lesson of great consequence to the Japanese Navy. Meteorologists plotted a typhoon as a circle, which they divided into four quadrants, numbered counterclockwise, starting with the upper right-hand quadrant, (assuming that the typhoon was moving in a northerly direction). During its transit through the No. 2 Typhoon, the Fourth Fleet discovered that the semicircle on the right, or east, was the area of greatest danger, because the winds of the typhoon are added to the background flow that causes the forward motion of the storm. Further, the Fourth Fleet encountered the highest and steepest waves, because the shifting direction of the winds, as the storm revolved around its eye, caused an interaction between between wave patterns moving in different directions. The waves encountered in that quarter made it clear that the Japanese Navy had, up to that time, dangerously underestimated the most extreme sea conditions possible in the north Pacific. Whereas Japanese warships had been designed to deal with wave configurations of no more than 1 to 20, naval hulls would need to be capable of withstanding far higher ratios. The Harukaze's navigation officer, Commander Sekino Hideo, recalled seas so mountainous that when the ship crested a wave, he could look down directly upon the destroyer ahead, as if viewing it from an office window. The report of these discoveries was so important to maritime safety and national security that it rated the highest classification. Only after the war was it made public.
Obviously, the extensive renovations of the navy's fleet units and the funds, time, and attention that they absorbed seriously delayed the Japanese Navy's preparations for war with the United States. Yet the ocean disasters of 1934 and 1935, as severe as their consequences may have been, in some ways worked to the Japanese Navy's advantage. It is difficult to say how a better understanding of weather affected fleet movements during the conflict, but it is true that Japan, unlike the United States, did not lose a single ship to wartime weather conditions. Second, without these disasters, the Japanese Navy might not have recognized the weaknesses of their ships and, in wartime, might not have had the time or funds to correct those weaknesses. Certainly, if one considers the combat performance of these particular cruisers and destroyers during the first two years of the Pacific War and their ability to absorb, as well as to inflict, a great deal of punishment, it is clear that these storms were ill winds that nevertheless brought the Japanese Navy reprieve.