If there are any achievements of which Japanese naval architects may feel justifiably proud when they look back on the Pacific War, the construction of the famous battleships Yamato and Musashi most certainly can be placed among the foremost. The largest ever built, these battleships displaced 69,100 tons and mounted nine 18-inch guns. The naval architects’ pride in the huge dreadnaughts was not diminished by the fact that both monstrous ships were eventually sunk by the planes of U. S. carrier forces before their powerful guns were able to wreak the terrific destruction against their principal intended targets—the U. S. battleships.
For their builders the tragedy of their loss lay in the drastic changes that naval warfare technique had undergone by the time those epochal battleships were ready for service. After consistent, almost superhuman efforts on the part of these naval architects, the Yamato was finally completed in early December, 1941, six years and nine months after her first blueprint was made. Ironically, however, the progress of the naval air arm by that time had made such a huge warship obsolete.
The construction of the Yamato-class battleships was not made possible by merely increasing the scale of past shipbuilding data as had been pointed out by Mr. Oscar Parkes in the August 5, 1949, issue of Engineering. The facts that these warships mounted 18-inch guns, the largest modern naval guns ever mounted on a ship, and that these ships were protected by armor capable of withstanding the same caliber projectile made their construction extremely difficult. Extensive studies and experiments, both fundamental and advanced, were unavoidable. In fact, more than two years had elapsed and 23 different blueprints had been drawn up before the final plans were determined in late March, 1937. As many as fifty experimental ship models were tested in the model basin to find the most effective shape.
Unfortunately, most of the invaluable data and information concerning the construction of the Yamato and Musashi were reduced to ashes in the disorder and confusion following the surrender of Japan in the summer of 1945. Such an irrevocable loss was deplorable to say the least. As a scientist who had participated in designing the ship from its beginning, I felt an obligation to leave a record of the construction of the Yamato while my memory was still fresh. With the whole-hearted cooperation and encouragement of those who supported my project, I wrote a long article on the subject which appeared in a Japanese scientific magazine, Shizen, as a series from January to September, 1950. These articles appeared in book form in the fall of 1952. This article is a condensation of the book.
Eighteen-Inch Guns
The unique feature of the battleship Yamato was her eighteen-inch guns. Until then the largest naval guns of the modern type ever mounted aboard a man-of-war were of the sixteen-inch size. However, a mere two-inch difference in gun diameter does not adequately describe the differences in the size, weight, and technical difficulties involved between ships mounting sixteen- inch guns and those with eighteen-inch guns. The weight of a sixteen-inch projectile was about 2,200 pounds; that of the eighteen- jumped to 3,200 pounds. The weight of a triple-mounted eighteen-inch gun turret was 2,774 tons, as heavy as a large-type destroyer. Technically, an eighteen-inch gun offered numerous difficulties, some of which seemed at first to be insurmountable obstacles.
It was obvious that industrially and economically Japan could not keep pace with the United States. Japan’s only resort, Japanese naval strategists believed, was to make each individual ship’s strength so great that even the resourceful and powerful industrial United States could hardly match it in a few years. This was one of the fundamental reasons why the Japanese made tremendous efforts to mount eighteen-inch guns on their new battleships.
Another consideration on which we Japanese put much importance was to build a ship of such size that the same type of ship which the U. S. Navy might build to cope with her could not pass through the Panama Canal. If Japan could build such a ship, she would surely enjoy a very desirable advantage, Japanese naval strategists reasoned. It was believed improbable that even the U. S. Navy could prepare two-ocean fleets. Based upon our study, we estimated that the biggest ship which could pass through the Panama Canal would be 63,000 displacement tons, have a speed of 23 knots or less, and mount ten 16-inch guns.
Original Plan
These two fundamental requirements naturally demanded a giant ship. As compared with the Mutsu, which mounted eight sixteen-inch guns, the weight of the Yamato’s nine eighteen-inch guns is well illustrated in the following table:
|
|
Yamato |
Mutsu |
|
|
|
(Y) |
(M) |
(Y)/(M) |
|
Weight of gunnery installations (tons) |
11,802 |
6,600 |
2.0 |
|
Armor |
23,500 |
10,400 |
2.3 |
|
Displacement |
68,200 |
37,00 |
1.85 |
It was in October, 1934, that the Bureau of Naval Construction was for the first time requested by the Naval General Staff to study the building of new battleships mounting eighteen-inch guns. As to speed, the original request of the Naval General Staff was approximately 30 knots. This was calculated on the assumption that new U. S. battleships’ speed would be 24 or 25 knots.
The first blueprint of the new battleship— not yet named the Yamato—to meet the above two fundamental requirements was drawn up in March, 1935. The planned ship was bigger than the actual Yamato. It was 294 meters in length, 41.2 meters in width, and displaced 69,500 tons equipped with 200,000 HP turbine engines which would give a top speed of 31 knots. Such a warship was too big even in the eyes of the Japanese strategists, who were then willing to reduce the speed requirement of the new battleship to some 27 knots. This was a difficult decision for the Japanese, who traditionally put much importance on the speed of men-of-war.
Subsequently, alternative blueprints were successively drawn up. And the semi-final blueprint which, except for the main engines, had substantially the same dimensions as the final blueprint, was drawn up in July, 1936. The semi-final plan called for the installation of turbine engines having a total of 75,000 HP to run two propellers and diesel engines with a total of 60,000 HP to run two other propellers. Since the second blueprint it had been a consistent plan in all other blueprints to install diesel engines as the main machinery. By that time, the Japanese Navy had developed a powerful two-cycle, double-acting diesel engine capable of developing more than 10,000 HP. It had been used as the main engine of the submarine tenders, Taigei, Tsurugizaki, and Takasaki, so that we were not apprehensive of employing diesel engines as the propelling machinery of the Yamato.
It was apparent that, although a diesel engine was slightly heavier than a turbine engine having the same power, the fuel consumption of the diesel was appreciably less than that of the turbine. Comparative data between turbine and diesel engines applied to one of the blueprints is shown below:
|
Shaft HP |
Weight of Engines (tons) |
SHP/ft.2 |
Necessary Fuel for 18 Knots—8,000 Miles (tons) |
|
|
Turbine |
Diesel |
|||
|
115,000 |
0 |
4,008 |
76.5 |
8,400 |
|
45,000 |
70,000 |
4,253 |
70.0 |
5,700 |
Final Plan
About two months after the semi-final plan was completed in July, 1936, the designers were confronted with an unexpected difficulty, which caused a drastic change to be made in the semi-final blueprint. A fundamental defect was found in the high-powered diesel engines which had been installed on the above-mentioned sub-tenders. Since the Yamato’s engine rooms were to be covered with 200-millimeter armor plate, it would be impossible to replace the engines after they were installed even if they happened to develop trouble. The fundamental defect found in the diesel engines to be installed aboard the new battleship forced designers to abandon the original plan, which was then changed to provide for the use of 150,000 SHP turbine engines as the propelling plant. It was in March, 1937, that this final blueprint was drawn up.
Principal dimensions thus concluded were as follows:
|
Length between perpendiculars |
244.0 m. |
|
Length over all |
263.0 m. |
|
Breadth maximum |
38.9 m. |
|
Mean draught (Full load condition) |
10.86 m. |
|
Displacement (Trial condition) (Full load condition) |
69,100 tons (when completed) 72,809 tons (when completed) |
|
Fuel load capacity |
6,300 tons |
|
Radius of action |
7,200 sea miles at 16 knots |
|
SHP |
150,000 HP |
|
Engines |
4 turbine engines |
|
Steam pressure & temperature |
25 kg./cm.2 325 degrees C |
|
Crews |
apprx. 2,200 (plan) apprx. 2,500 (actual) |
Features of the Hull
One of the notable features of the Yamato’s hull was that her displacement length ratio was great, and her speed length ratio small, compared with other battleships. While those ratios of the Nagato were 98.14 and 1.001 respectively as compared with 101 and 0.852 for the British battleship Nelson, those of the new Japanese battleship were 112.2 and 0.94 respectively. Moreover, her prismatic coefficient was 0.612, perhaps the highest figure among all the men-of-war in the world. This meant that she was a broad, fat, and shallow draught vessel for such a big displacement.
To make the Yamato’s draught as shallow as possible was a primary consideration from the standpoint of harbor facilities of the naval bases in Japan. Nevertheless, her draught when fully loaded reached 10.8 meters (35+ feet), a depth which necessitated the dredging of some areas of our naval bases and extensive portions of the water approaches to dry docks which were to be used by warships of this class.
How to reduce the hull resistance and increase the propulsive efficiency was the next problem which the designers strove to solve. Tests were conducted with various hull models in the experimental model basin of the Naval Technical Research in Tokyo. This basin was the largest one in this country, having a length of 245.5 m., a width of 12.5 m., and a depth of 6.5 m.
These thorough and extensive experiments led to the adoption of a gigantic bulbous bow, the size of which few other naval architects had ever planned. The result achieved was unique. The reduction of the hull resistance by the use of this bow reached 8.2% at a speed of 27 knots. This figure exceeded what Mr. Oscar Parkes estimated to be —5 to 6%, which was a reasonable estimate for an ordinary type bulbous bow.
By improving the fitting of the shaft bracket and the bilge keel, a further reduction in hull resistance was achieved. Represented in terms of effective horsepower, the former resulted in the saving of 1,900 EHP and the latter 475 EHP. Altogether, including the reduction in resistance by the use of the bulbous bow, these savings totalled 7,910 EHP, or 15,820 SHP.
In the full-power trial run, the 69,500-tons vessel, powered by 153,553 SHP, made 27.46 knots. EHP at that time was calculated at 76,700 HP, the propulsive efficiency reaching 50.0% The propulsive efficiency at her standard speed, 18 knots, proved to be 58.7%. Such efficiency was seldom obtained by other vessels of the Japanese Navy.
Another important feature was the extensive use of lap-joint in the midship part of the shell plating. The butt joint had long been used in shell plating to make the shell surface smooth, thus reducing its frictional resistance. However, a serious defect had been found in the outer bottom butt-joint plates of the Isuzu-class light cruiser and Fubuki-class large-type destroyers. This led to apprehension regarding the use of butt- joint plates in the Yamato’s shell. On the other hand, it was learned that frictional resistance was greatly affected by the surface of the fore and after parts of a ship where the water pressure was greater than at amidship. Based on this finding, butt-joint plating was only used in the fore and after parts of the Yamato; the remaining part was covered by lap-joint plating. This method proved very effective when the ship was completed.
Hull Structure
In the hull structure, too, several new measures were adopted to ensure the required strength and, at the same time, to save weight. Here are some examples:
First, some of the armor was fitted to serve as hull strength members. The lower side armor was fitted to serve dually as longitudinal members. This was an unique method that the Japanese Navy had applied to medium armor plating, since Dr. Hiraga, then the leading naval architect of the Japanese Navy, had applied it for the first time to the light cruiser Furutaka, whose unique characteristics surprised world shipbuilding circles at that time.
Second, electric welding was employed extensively, except in the longitudinal member. The Japanese Navy was rather early in adopting this type of welding in the ship’s hull construction. As early as 1932, this welding was used extensively in building the minelayer, Yaeyama. The 10,000-ton submarine tender Taigei, which was completed in March, 1934, was the first ship in the Japanese Navy with a completely welded shell.
However, two historic sea disasters which later occurred in the Japanese Navy required a thorough investigation of shipbuilding. On March 12, 1934, the latest type 700-ton torpedo boat, Tomozuru, capsized outside the Sasebo naval base in heavy weather. On September 26 of the following year, the Fourth Fleet struck a heavy sea in which two large type destroyers broke in two and others sustained heavy damage. An extensive and thorough investigation was then carried out. The wisdom of the welding was also reviewed, and it was decided not to use the welding in such an important portion as the longitudinal structural members.
In fact, most of the Yamato’s upper structure was constructed by means of the electric welding. The largest welded block for the Yamato was 11 meters high and weighed 80 tons. The total length of the welded portions of the Yamato reached 463,784 meters, and the total number of welding rods used in the construction added to 7,507,536. By the way, the total number of rivets used was 6,153,030.
Thirdly, the main portion of the longitudinal structure was constructed with ducol steel, while other portions were made with mild steel.
Fourthly, the central longitudinal bulkhead was constructed in duplicate. It was to support heavy, 200-millimeter long, armored deck plates, 38.9 meters wide at the largest breadth. To ensure the reliability of the electric circuit, the central ringmain electric circuit ran through the watertight compartment inside this central bulkhead.
Her flush-type weather deck from bow to stern, giving her an extraordinary appearance for a battleship, was another unique feature. The idea was to make the longitudinal members continuous so as to be most effective and, at the same time, to save the structural weight. This method had been adopted in building Japanese warships ever since it was first applied to the light cruiser Furutaka.
The Yamato’s stern casting, which had to support her heavy 2,490-ton stern portion was an extraordinarily large one, too. Made of cast steel, it weighed 91.3 tons.
Terrific Blast of 18-Inch Guns
Terrific effects were anticipated on numerous installations aboard the Yamato by her huge gun blast. While the blast of two 16- inch guns simultaneously firing was figured 3.5 kg./cm.2 at a point 15 meters from the guns’ muzzles, that of the Yamato's three 18- inch guns was approximately 7.0 kg./cm.2 at the same distance. This was an immense figure, since it was believed that the blast pressure of 0.28 kg./cm.2 was capable of destroying boats on board the ship and that of 1.16 kg./cm.2 of tearing the clothing from men and rendering them temporarily unconscious.
This meant that nowhere on her weather deck could any boat be safely kept while her main batteries were firing—AA guns as well as AA machine guns had to be protected by a shield from the blast of the main batteries. Vedette boats, other launches, and cutters were to be kept inside of the boat hangars which were installed on both sides of the stern. Ventilators on the weather deck were reduced to a minimum and installed at places where the blast was least effective. The idea of protecting AA batteries from the blast by shields, enabling them to fire while the main batteries were in use, greatly restricted the installation of the antiaircraft weapons. After the outbreak of the war, however, the importance of powerful antiaircraft weapons was keenly, and later bitterly, realized. This restriction was then lifted, and many machine guns were installed on the weather deck without a shield to protect them from the blast.
Machinery Arrangement
The Yamato's 150,000 HP propelling machinery, using 25 kg./cm.2 and 325°C. steam, was not unique at all, but its arrangement in four rows was noteworthy. Its twelve 12,500 HP boilers were arranged in four rows, three in each row, each comprising a separate cell. Three boilers in one row were connected to one of four turbine engines which were also installed in four rows. From the viewpoint of damage control and armor protection, this was naturally the most desirable arrangement. However, only a large breadth vessel such as. the Yamato-class battleship could possibly have such an arrangement. How the Yamato improved her shaft horse power per square meter of engine room floor may be seen in the following table:
|
|
SHP |
Engine Room Floor Ae (m.2) |
SHP/Ae |
|
Nagato |
82,300 |
516 |
158 |
|
Yamato |
150,000 |
640 |
238 |
Armor Protection
The Yamato was the heaviest armored man-of-war ever built. Her vital parts were protected on the sides by 410-mm. Vickers-hardened armor plates capable of withstanding the force of an 18-inch projectile fired at more than 20,000 meters. Her 200-mm. MNC deck plates enabled her to withstand an 18-inch projectile fired at less than 30,000 meters. The 200-mm. deck armor could be penetrated only by a 1,000-kg. armor-piercing bomb dropped from the height of 3,400 meters or more. Even part of the upper-most deck, in addition to the armor- protected vital part, was protected by 35- to 50-mm. CNC, the latter being sufficient to repel a 250-kg. bomb dropped by a divebomber.
In designing the Yamato, efforts were made to minimize the length of the vital part that had to be protected by heavy armor plates. Comparisons with other battleships are as follows: The ratio of the length of the vital part to the water-line length of the Yamato was 53.5%, of the Nelson 54.7% and of the Nagato 63.15%. Despite her lower ratio, however, the Yamato’s stability under damaged condition was designed to be better than that of other Japanese capital ships.
Thick armor plates around the vital part were not the only protective features provided on the Yamato. Her steering engine rooms—(the Yamato had two steering apparatuses, the main and auxiliary, to secure her steering ability)—were protected by armor as heavy as that given to the other armored portion. Another feature was the fact that the bottoms of the Yamato’s magazines were protected by 50- to 80-mm. armor plates. These plates extended from the bottoms of the magazines across water-tight compartments inside the double bottom of the shell. The idea was to protect them from the explosion of a hostile torpedo or mine from underneath the ship.
Another feature was the perforated type of armor plate for her smoke stack protection rather than the conventional coaming armor. After careful tests, 380-mm. armor plating with perforations of 180 mm. in diameter (the total area of the holes being less than 55% of the whole area of the plate) was adopted. In addition, the inclined surface of the stack was protected by 50-mm. armor which would detonate bombs before they exploded on the surface of the perforated plating where the output of smoke from twelve boilers escaped. This new method of stack protection resulted in a substantial reduction of weight.
The percentage of the Yamato’s weight used entirely for protection compared with the total tonnage was high. While that of the Nagato was 30.7%, the highest figure among Japanese warships before the Yamato, that of the Yamato was 33.1%.
Armor Plates
Some important factors should be revealed in connection with the Yamato’s armor plates, which were completed after ten years of earnest study and effort on the part of naval technicians. The front and side barbette armors, which had to resist the terrific kinetic energy of a 1,460-kg. projectile having the speed of approximately 500 meter's per second, consisted of 560-mm. and 410-mm. armor plates respectively. An extremely hard surface was a requisite factor for such armor plate, but the ordinary method of cementation was expensive and incapable of giving the result desired for such thick plates. Instead of the cementation method, therefore, a special method was adopted to harden the surface of such thick armor plates. This new method proved very effective: not only could it harden the portion reaching as thick as 140 mm. from the surface, but it also greatly reduced the production cost.
Theoretically, the resistance of armor plate to a projectile is not uniform. It is least at its edge. This means that the larger a piece of armor plate the greater resistance can be expected. The Japanese Navy ignored expense in expanding the necessary facilities to manufacture larger pieces of armor for the Yamato-class battleships. According to records, about $10,000,000 were spent to expand steelplate manufacturing facilities. The dimensions of a piece of side armor manufactured in these facilities were as follows: 5.9 m. by 3.6 m., 21.2 square meters, 410 mm. thickness, and 68.5 tons.
How to construct a sufficiently strong armor-shelf, especially at the lower edge of the 410-mm. side armor, to resist the terrific shock of a projectile hit, was a big problem also. The Yamato's side armor was equipped so as to drive a wedge with the wedge angle of 10 degrees at its lower edge when struck by the shock of a hit, but even this method proved insufficient after she was commissioned in the service. In the war, she was struck by a torpedo and her side armor at the point of impact was indented about one meter.
Another feature in connection with armor protection was the 9-mm. ducol steel plates which extended along 700 mm. underneath the armor deck. Their purpose was to protect from possible splinters such as armor bolts and rivet heads when the armor deck was hit by an enemy bomb or projectile.
Water-Tight Compartments
Much attention was also directed toward the maintaining of buoyancy by increasing the number of water-tight compartments. The result of these efforts will be seen in the following table (the number of water-tight compartments):
|
|
Below |
Above |
|
|
|
Armor |
Armor |
Total |
|
|
Deck |
Deck |
|
|
Yamashiro |
574 |
163 |
737 |
|
Nagato |
865 |
224 |
1,089 |
|
Yamato |
1,065 |
82 |
1,147 |
The reason for fewer water-tight compartments above the armor deck as compared with other ships was the fact that the Yamato’s armor deck was comparatively high above sea level.
Turning Ability
The Yamato's turning ability was excellent. Her tactical diameter, advance, and maximum heel when turned by the maximum rudder angle of 35 degrees at a speed of 26 knots were 640 meters, 589 meters, and 9.0 degrees respectively. These figures were considered superior when compared with those of other battleships. Her comparatively small heeling angle in a turn, advantageous from the standpoint of evading bombs and torpedoes, stability, and fire-direction, was attributed to her GM (metacentric height), which was 2.6 meters at her trial run. This figure was once criticized by a foreign critic as being excessive, but this was not true. Her rolling period was 17.5 seconds, a figure arousing pride from the shipbuilding point of view.
As already related elsewhere in this article, the Yamato had two rudders, the main and the auxiliary, instead of the twin-rudder system of ordinary large warships. Originally it was planned to install two rudders, one each fore and aft, in view of the fact the German battleship Bismarck finally lost her maneuvering ability because of damage to her rudders in the early part of World War II. But, the plan was later changed so as to install the auxiliary rudder about fifteen meters ahead of the main one.
In the trial run of the Yamato, however, an unexpected feature was discovered in the use of this auxiliary rudder, to the disappointment of designers. So great was the turning momentum of the Yamato once she had begun turning that the auxiliary rudder alone could not reduce the momentum sufficiently to make her resume course.
Stability and Trim Under Damaged Condition
Compared with other Japanese battleships, the Yamato was well designed to survive in a damaged condition. This was well demonstrated in her last hours and those of her sister ship, the Musashi, although both were eventually sunk.
The Yamato's fore freeboard was 10 meters and aft was 6.4 meters. These figures were remarkable compared with the Nagato’s figures, which were 7.9 meters and 4.8 meters, respectively.. Accordingly, her reserve buoyance reached as much as 57,450 tons, showing a sharp contrast with 29,292 tons for the Nagato and 21,300 tons for the Fuso.
The Yamato was designed also to remain fairly stable in a damaged condition. Although her fore and aft parts, other than the protected portions, were flooded, it was believed that she could maintain her stability until she listed to 20 degrees.
It was also believed that her trim capacity would enable her to function with her fore freeboard reduced to 4.5 meters, even if her fore part was completely destroyed and flooded. The battle report of the Musashi during the Sho Operation in the fall of 1944 stated that her fore part was awash before she eventually sank. This was due to the fact that her water-tight compartments beneath her fore magazine rooms, as well as both sides of her armor-protected portions, were flooded.
Flooding and Pumping System
The flooding and pumping system of the Yamato was designed to satisfy the following requirements: (1) The resultant heel and trim from the first torpedo hit could be recovered within 4 degrees heel and 2.3 meters draft difference between fore and aft within five minutes after the damage control system was started. (2) The resultant heel and trim from the second torpedo hit could be controlled within twenty minutes, according to the above-mentioned standard.
By flooding the opposite side’s damage control tanks, the Yamato could also be recovered by 9.8 degrees at the maximum and another 4.5 degrees heel could be added by shifting fuel to the opposite side tanks. Altogether, it was believed that this system could enable the Yamato to return to almost even keel from a list of 18.3 degrees.
Other Features
Unlike the ugly children’s building-block like masts which had been traditional features of Japanese battleships, the Yamato's tower fore mast was much improved and streamlined. Its frontal area and side area were 159 and 310 square meters respectively, showing much improvement over those of the Nagato, which were 162 and 371 square meters respectively.
The tower consisted of two concentric cylinders, atop of which a triple mounted huge fifteen-meter range finder (one of which was a stereo-inverto type) and the fire-director were mounted. Precautions were also taken to protect the nerves of the ship from the strafing of enemy planes. The inner cylinder, 1.5 meters in diameter, was made from 20-mm. DS steel, inside of which ran communications lines. Space between the outer and inner cylinders was utilized for passages, staff-briefing rooms, etc.
Even in accommodation facilities, the Yamato had remarkable features. She was the first Japanese warship to be equipped with an air conditioning system. Although this comfort was not afforded to all the living quarters, the Yamato had the favorable reputation among sailors as being the most comfortable ship in the Japanese Navy.
Particular Construction Preparations
When the construction of the Yamato-class battleships was planned, there was no shipyard in Japan capable of building such a giant vessel without expanding its facilities. Since the Japanese Navy intended to construct four Yamato-class battleships successively, special preparations for their construction had to be undertaken in selected shipyards. Some of these arrangements consisted of expanding dock capacities, building a special transport capable of carrying a large and heavy 18-inch gun turret, and hiding such a large vessel behind sisal rope curtains for security reasons.
The depth of the construction dock at the Kure naval yard, in which the Yamato was actually built, was deepened about one meter so that the heavy Yamato might be floated in the dock. The capacity of the gantry crane straddling the dock was raised to 100 tons in order to lift heavy armor plates. Moreover, about one-fourth of the dock from its extreme end was covered by roof to prevent its being seen from a prominent hill nearby.
In the Yokosuka district a large dry dock for this size battleship was built, and the third ship of the Yamato-class, later named the Shinano and converted into a carrier, was built there.
The Nagasaki yard of the Mitsubishi Heavy Industries Co., Ltd., was the only other available shipyard capable of building a Yamato-class battleship, even with some expansion of its facilities. Unlike Kure’s building dock, a slipway was to be used for the construction. Technically, the launching of an at least 30,000 launching deadweight tons vessel raised various difficult problems, the details of which will be described elsewhere in this article. Not only was the slipway strengthened, but work shops and piers were also expanded or strengthened. The over-all area of the expansion of the work shops reached a total of almost 240,000 square meters. Floating cranes of 350 tons and 150 tons were built and installed at that shipyard to lift heavy armor plates and gun fittings. At Sasebo, one of the three major naval bases in Japan, a dry dock capable of accommodating a Yamato-class battleship was also built.
Some of the measures taken to safeguard the security of the Musashi were interesting. The slipway on which the Musashi was being built was covered by a sisal rope curtain. The total length of rope used reached 2,710 kilometers, and its weight totalled 408 tons. This great consumption of sisal rope caused a temporary shortage of this item on the market, of which fishermen complained.
One more thing to be added here was the construction of a transport vessel to carry the 18-inch guns from Kure to either Nagasaki, where the Musashi was being built, or to Yokosuka, where the third ship was to be built. These 18-inch guns and their turrets were manufactured at the Kure naval yard, and they could be transported only by the ship specially built for that purpose.
Launching of the Musashi
The launching of the Musashi—her launching weight of 35,737 tons being second only to the 37,287 tons of the Queen Mary— deserves to be described in greater detail. It is noteworthy that efforts were made to minimize the pivotting pressure by making the declivity of keel 30/1000. This made it possible to reduce her pivotting pressure from the originally estimated figured of 8,300 tons (that of the Queen Mary being 8,459 tons) to 7,870 tons. Another point of interest was that a 13-foot wide slipway, the widest ever used in the shipbuilding industry throughout the world, was used for the launching of the Musashi. Such a wide slipway was used to make the average pressure upon the slipway less than 2 tons per square foot. From a technical point of view, such a wide slipway was far from easy to construct.
Extraordinary efforts were also made to reduce her launching weight as much as possible. From the standpoint of providing the necessary hull strength, the hull of the Musashi had to be completed up to the weather deck before she took to the water. In this case, it was feared her launching weight would be* excessive. It was then planned to install the armor deck after she was launched. But this was extraordinarily difficult because the decks above the armor deck were to be constructed on the armor deck. It was then necessary to install temporary bulkheads in the place of the armor deck on which to construct the upper decks. After she was launched, the deck armor plates were installed to replace those bulkheads. All this was accomplished only after extraordinarily hard work.
The hush-hush policy with regard to the construction of those battleships from the very beginning required the historical launching of the Musashi to be done by stealth. In the afternoon of the day preceding the launching, all the entrances leading to the slipway where the Musashi was being built were closed without notice and communications to the outside were severed. Workers, who were for the first time told the launching hour, labored throughout the night, and the Musashi was launched in the early morning of the following day with little of the ceremony which otherwise ought to accompany such an occasion. In Nagasaki city, too, especially on the opposite coast side of the shipyard, a heavy guard was maintained that early morning to keep people from observing the launching.
Couldn’t the Sinking of the Yamato and Musashi Have Been Prevented?
After reading the above description of how strongly the Yamato and the Musashi were constructed, a reasonable question one might raise would be, “Why, then, were they eventually sunk by only aerial torpedoes and bombs?” Were their losses unavoidable?
According to the detailed battle report of the Musashi in the battle for Leyte Gulf in the fall of 1944, she had been hit by a total of seven bombs, nine torpedoes, and more than fifteen near misses by 1253 hours on that day when the second wave of the U. S. carrier planes had finished their attacks. As a result of those hits, her fore part was flooded up to her third deck, and she listed heavily to port. Her speed had to be reduced to 22 knots. This, however, did not constitute a fatal blow. As a matter of fact, her vital armor-protected part still remained intact, and her list was recovered to almost even keel by use of the damage control system.
It was only after the third round of the U. S. attack, in which another ten direct bomb hits and eleven torpedo hits were scored, that the Musashi lost most of her maneuverability due to her worsened bow trim. Her bow was so deeply awash that her speed had to be reduced to only 6 knots. Yet she still could recover her list by 4 degrees. Toward the evening of that day, about four and one-half hours after the third attack of the U. S. aircraft ended, the situation suddenly became worse. Her list to her port increased, and the giant battleship finally went down.
The immediate cause for her sinking had to be ascribed to the fact that her fore portion was flooded and the fore deck was awash. As a result her efficient area of water- plane was so reduced that she had reached the worst possible condition. When her list had gone beyond the limit of its stability for a damaged condition—about 30 degrees— she eventually sank. As already related elsewhere in this article, the expected bow trim increase when her whole fore part was flooded was 5.5 meters draft increase in her bow, still leaving some meters freeboard. The fact that her bow draft increase reached 8.0 meters and her fore part was awash showed that her water-tight compartments beneath her magazine rooms and both sides of her armor-protected portion, as well as the fore unprotected portion, were all flooded due to damages sustained.
Another cause for the loss of the Musashi was that those flooded portions gradually increased as time passed. This may be due to the fact that sufficient strength was not necessarily given to other portions than the main hull structure in order to reduce the weight of those portions as much as possible. As a matter of fact, the longitudinal and transverse bulkheads in the fore and aft and lower decks were not sufficiently strong.
Data on the Yamato are not available in sufficient detail to comment upon. According to the statement made by Capt. Jiro Nomura, the executive officer of the ship, she was attacked by an overwhelmingly superior number of U. S. carrier-borne planes which numbered over 1,000. As a result, she was hit by at least seven large-type bombs, numerous small-size bombs, and twelve aerial torpedoes. Those aerial torpedoes were concentrated on the port side of the Yamato, which may have contributed to her rather quick end. She went down about two hours after the last wave of planes had ended its attack.
The sinkings of the Yamato and the Musashi by U. S. carrier-borne planes alone certainly did not prove that they were unusually vulnerable. They eventually sank only after they had displayed their immense resistance to the limit as planned. Admittedly, though they had some defects, they proved to be the toughest men-of-war ever built, at least by the defunct Japanese Navy.