Shinano: The Jinx Carrier

After the pyramids of Egypt and the Great Wall of China were the three ships of Yamato: wonders of the world, yet like the lofty pyramids and the long wall, great follies indeed.”

It is a wiser and certainly healthier nation that can today say this of Yamato and her two sisters, and see in them a symbol of Japan’s futile and tragic war effort. As symbols, the super-dreadnoughts Yamato and Musashi, together with the huge aircraft carrier Shinano, are rapidly becoming legends, perpetuated by American and Japanese naval enthusiasts alike.

Although considerable interest has been shown recently in the design and fate of the 64,000-ton, 18-inch gunned battleships, Shinano, third ship of this class later converted into the largest carrier ever built by a world sea power, has been neglected by historians and seems today the best candidate for legend.

There are several reasons for this obscurity, the most obvious one being the complete destruction of documents relating to Yamato-class ships and their subsequent modifications. The pre-surrender burning of the Imperial Naval Technical Bureau (Kampon) archives at Ofuna left only a few naval officers familiar with top secret details of Japanese wartime ship construction. These men assisted the Occupation to bridge the huge gaps brought on by destruction of ships and official documents. In many instances, however, blanks remained, to be filled in only gradually during the post-war years in the form of books and magazine articles, and as personal memoirs. Until recently considerable information concerning the Yamato-class battleships and Shinano existed only in the memories of those officers associated with the Kampon during the war.¹

Yamato and Musas hi have both come in for all of the post-war spotlight on this remarkable class of ships. The suicidal dash of the former during the Okinawa operation and her agonized sinking, just five months after Musashi’s fatal encounter with U. S. carrier planes in the Battle for Leyte Gulf, attracted the attention of readers in Japan and the United States alike.

Shinano’s ignominious demise less than a day after setting sail on her maiden voyage, prompted no such interest. And understandably so; for Shinano's jinx-like story is considerably more complex, involving an interplay of ideas on a much less popular level of naval interest. Shinano’s story is not in her operations but rather in her conception and construction—a four year process, during which tens of millions of yen and long hours of labor were needlessly expended in the creation of what was then thought would be a “majestic and unperishable castle of the seas,” but which ended up instead an unsalable mass of scrap at the hands of an alert American submarine—the largest single underseas kill of World War II.

Conception—1939-1942

H.I.J.M.S. Yamato and Musashi, first of the Japanese super-dreadnoughts, were projected shortly after Japan’s abrogation of the Washington treaty limitations. Designed by Vice Admiral Keiji Fukuda and Captain Kitaro Matsumoto, both of the Kampon, the two Yamato-class battleships were laid down in 1937 at Kure and Nagasaki.

Shinano and a fourth unnamed BB (designated No. 111) of the same design were projected in 1939. Shinano was laid down at Yokosuka naval base, April 7, 1940, in an especially constructed dry dock concealed behind high sandstone cliffs. No. Ill was begun somewhat later in the year at Kure naval base. Elaborate screens concealed the dock from curious eyes.

As Shinano and No. 111 grew in their huge graving docks, plans were completed for the 1942 Fleet Replenishment Program. This program called for the construction of three more super-battleships. One or possibly two of these were to be modified Yamato-class BB’s, but with some of the secondary batteries removed and a higher proportion of AA- guns installed. A third modified Yamato type went to the drawing boards of the Kampon in 1938. This newest modification was designed to carry six 20-inch rifles, two mounted in each of three turrets in somewhat the same arrangement as the H.M.S. Repulse.

This ambitious program, as planned before Pearl Harbor, also included plans for building a 50,000-ton super-carrier (an enlarged and much better protected version of the Taiho) and two 33,000-ton battle "cruisers, designed to stand up against the United States’ Alaska CB’s. The original design of the big cruiser called for three 12- inch triple batteries, and was well along when high ranking officers of the Gunreibu proposed that the designs be made over so that six 14-inch rifles in three double turrets replace the 12-inch batteries. Designers at the Naval Technical Bureau, inured to such interruptions, went back to work, but their plans were dropped for good after the outbreak of hostilities late in 1941.

Meanwhile, the realities of approaching war brought staff members out of the clouds. In the fall of 1940 the Emergency War Program of 1940 was promulgated. Plans were made for augmented carrier construction and modification.

At Yokosuka work on Shinano was temporarily slowed down so that shipbuilding efforts could be channelled to the more urgent aircraft carrier and conversion programs. Work on the battleship continued, but was almost stopped by this emergency construction.

The fourth Yamato-class BB in building at Kure was not far enough along to warrant further expense of materials and manpower. In November, 1941, part of the vessel was scrapped to make way for priority construction.²

Shinano was all but forgotten until the Pearl Harbor and Malaya actions brought battleship construction back into the limelight. Air-minded Japanese argued that U. S. and British capital ship losses to carrier- based aircraft during the first days of the war emphasized the futility of putting tremendous efforts into the building of Yamato-class battleships. This point of view apparently won out, for it was decided to drastically cut down on Shinano's building.

If Pearl Harbor cast doubts upon Shinano’s value to the Empire, it was the Battle of Midway that saved the ship. Midway had a profound effect upon Japanese carrier design. In the momentous fourth of June battle, 1942, aircraft from Enterprise, Hornet and Yorktown dealt Admiral Nagumo’s fast carrier striking force a blow from which the Imperial Navy never quite recovered. Four carriers, Akagi, Kaga, Hiryu and Soryu, their flight decks cluttered with aircraft rearming and refueling, were hit by American divebombers. Three of the Japanese ships, burning deadly gasoline and ammunition fires, were abandoned; a fourth, mortally wounded, was sunk by a patrolling American submarine.

When the Combined Fleet limped back into Japanese waters the Imperial staff was already planning new carrier construction. Midway had pointed out serious short-comings in Japanese carrier design. It was the opinion of some Midway survivors that the answer to American divebombing attacks lay in constructing carriers with heavily armored flight decks and better protected fuel and ammunition stowage spaces. Damage control methods, already at peak efficiency in the Imperial Navy, also came in for close consideration, with Midway veterans suggesting improvements in ordnance handling and fire-fighting methods.

Any hopes to revive the 1942 Fleet Replenishment Program were drowned by the wave of concern which swept through Imperial Headquarters after Midway. Out of post-Midway thinking came the Modified Fleet Replenishment Program of 1942, calling for 15 carriers of a modified Hiryu class and five of an improved Taiho class.³

It was recognized that construction of carriers embodying lessons learned at Midway would be a long-term project. Even with top priorities, few of the new ships would be ready for combat before mid-1945. And 1945, some feared, might be too late.

Attention was therefore focused upon existing ships capable of modification to aircraft carriers. Anything that could conceivably serve as a flight platform was considered a candidate for conversion. Prominent among the seaplane tenders, tankers, merchant ships, cruisers and battleships slated for alteration⁴ was the hulk of Shinano.

Shinano’s conversion was the idea of the Chief of the Naval Technical Bureau, Vice Admiral Sei-ichi Iwamura. Like other high ranking Japanese naval officers, Iwamura was deeply concerned over Japanese carrier losses at Midway. He saw in Shinano an opportunity to place an aircraft “carrier” in combat more rapidly than would be possible under the costly new construction programs.

Iwamura, working closely with Vice Admiral Keiji Fukuda, dean of Japanese naval architects and guiding light in all major Japanese warship construction, planned to convert Shinano into a strong floating air base, capable of retrieving, launching, and supplying naval aircraft operating from land bases or other ships. Shinano, carrying no planes of her own, nor capable of storing them, was in this first plan to play the part of a combatant auxiliary—a sort of aircraft “tender.”

Fukuda and another well known figure in Japanese warship design, Captain Shigeru Makino, went to work on preliminary designs while Shinano was again readied in Dry Dock 6 for her forthcoming conversion. But before work on Shinano's new design was finished staff members in naval air headquarters urged the Kampon to modify their designs, making Shinano into a true aircraft carrier, capable of maintaining her own aircraft. Iwamura acceded to these requests but included space for only 18 fighters in later plans. Having secured this concession, naval airmen then demanded that the Technical Bureau provide space for additional attack planes. At this point the Gunreibu, standing between the two factions, urged them to stop quibbling and get to work on anything that could be ready for sea in the shortest possible time.

Fukuda and Makino had a very difficult time reconciling the two points of view. But final plans, calling for a 68,000-ton, island-type CVB, capable of handling 18 VF, 18 VA and six scouts and supplying many more aircraft, were ready in September, 1942.

Construction—1942-44

Shinano was therefore a compromise. As the assistant designer of Yamato, Captain Kitaro Matsumoto, was to say later,⁵ it was  a very strange looking compromise indeed, ill conceived and too hastily rushed to completion. In its very design, and certainly in the spirit with which it was constructed, were the seeds of Shinano’s own destruction.

Although work began on the carrier before summer was out, it was not until later in the year that construction got into high gear. According to Matsumoto, a great deal of enthusiasm went into Shinano’s building. Its top secret classification failed to keep yard workers from taking unusual interest in the conversion. To some the rejuvenated ship became a symbol and a hope.

Conversion of the former Yamato-class battleship into a carrier proved almost as big a job as a new construction. From keel to main deck Shinano was essentially the Yamato, with double and triple bottoms, armored bulges below the waterline, and heavily armored magazines, steering engine rooms, machinery, and fuel spaces. Onto this it was planned to graft the structure of an aircraft carrier, complete with armored flight deck, island, hangar, and aircraft repair and ordnance stowage spaces. This conversion was to become a formidable construction problem.

Greatest emphasis was placed upon armor protection, Shinano’s major asset. Below the waterline the ship was protected by large armored bulges to minimize torpedo damage. At the waterline the carrier was defended by an eight-inch main belt of armor, in contrast to the 16-inch protection in the same places on Yamato and Musashi. A triple bottom in the machinery spaces gave added protection against mines.

Significant among internal modifications was conversion of Shinano’s magazines. Barbettes and magazines, seven inches thick, were converted to handle aviation ordnance. High speed armored elevators were installed to take bombs, torpedoes, and AA-ammunition directly to the flight deck—a lesson of Midway.

Above Shinano’s main deck, conversion was completely along carrier lines. Since the four-inch armored deck had already been laid down, this was the point at which work was begun on the hangar deck. Only one hangar deck was included in the revised designs. Center of gravity and vertical intensity considerations, added to the fact that the main deck was already down, militated against giving the big carrier two hangar decks, as in Taiho and Zuikaku. The ship consequently had a rather small aircraft complement in comparison to her size.

In Shinano the hangar deck was divided in two parts by an armored vertical bulkhead, and splinter protected by a half-inch armor overhead. The forward part of the hangar deck was designed to handle 18 Reppu fighters of the modified Zero design. The after hangar deck was big enough to house 18 Rynsei attack planes. Six Shiun scout planes rounded out the ship’s air complement.

The Battle of Midway made itself felt in construction of the hangar deck bulkheads. The enclosed sides of some of the Midway carriers made gasoline fires turn the ship’s hangar deck into an inescapable oven. Furthermore, it was difficult to jettison ordnance stowed on the hangar deck in the event of serious fires. In Shinano such fire hazards were minimized by making the forward two- thirds of the carrier hanger deck open, with rolling steel curtains installed for rough seas and night operations. The after third of the hangar deck was completely enclosed and protected by two-inch steel plate.

Midway impressed itself in still another way on the giant carrier’s construction. A fortunate dispersal of 1,000-pound bombs among U. S. aircraft attacking Japanese carriers at Midway was in part responsible for the terrific initial destruction in the June fourth battle. Shinano’s flight deck and elevators were therefore designed to withstand the blast of American 1000-pound bombs. Unlike Taiho, which was protected only between elevators and immediately over the hangar deck, four-inches of armor protected most of Shinano’s flight deck. Supported by closely spaced 31-inch box beams was a bottom layer of three-quarter inch steel plate, followed by a main three-inch armored layer and topped with a thin, shock- absorbent latex-sawdust-cement composition.⁶

Shinano’s armor, from bottom to super-structure, made it the heaviest warship ever constructed: 17,694-tons, or one third, of the carrier’s 68,000-ton trial displacement consisted of defensive armor.

Another big problem handed to Shinano’s builders as a result of the Battle of Midway was the location and protection of fuel voids. At first it was considered necessary to keep the fuel tanks as far from the engine room as possible. However, one group of Japanese officers believed that fuel tanks were best protected by the main belt of armor. In Shinano the opposite view prevailed. Fuel voids were placed most distant from the main armored section under water and protected by tapered one to three-inch armor plate. In many Japanese carriers protection of av-gas spaces was augmented after Midway by surrounding fuel spaces with water. This was to be Shinano’s additional protection: 2,000- tons of water to encase her inflammables.

Taiho’s sinking by the U.S.S. Alhacore in June of 1944 brought fuel stowage into prominence again. As a result of experiments conducted at Kure, Zuikaku and five other of the remaining Japanese carriers⁷ were slated to have cement-filled bulges constructed fore and aft on both sides over av-gas voids. However, only Zuikaku was thus protected; and that protection could not save her from sinking afterwards.

These experiences which occurred during Shinano’s construction and the resultant experiments conducted by the Naval Technical Bureau culminated in minor changes in the carrier’s fuel space protection. When Shinano put to sea in November, 1944, some of her fuel voids were protected by cement as well as water.

On the basis of lessons learned at Midway, Shinano’s ventilation system was given considerable attention. To prevent hangar deck explosions from spreading deadly fumes throughout the ship’s ventilation system— an accident that knocked out at least one Japanese carrier at Midway—all ducts were armored with one to 1½-inch armor.

Ordnance handling also came in for close scrutiny after the grim lessons of Midway had been impressed upon the Imperial Navy. Time and again it was emphasized that explosives handling must be done in the open air and in the shortest possible time. Hangar deck loading, standard operating procedure before Midway, was ruled out as exceptionally risky. Furthermore, Nagumo’s fateful decision to switch ordnance loads at Midway perpetuated a healthy respect for planned rearming discipline. This was particularly reflected in Shinano’s ordnance handling equipment and in post-Midway deck evolutions.

The fire conscious constructors of Shinano did everything in their power to minimize the danger of spreading fires. Wooden structures were eliminated. A special fire-resistant paint was developed in time to be used on the carrier. An important addition to the ship’s fire protection apparatus was a Japanese- designed bubble fire extinguishing system. In contrast to “foamite,” in use at that time aboard American carriers, Shinano was fitted with soap solution tanks feeding specially designed nozzles. The soap bubble extinguishing system, previously installed in commercial ships only, became standard equipment in Japanese carriers after Midway.

Shinano was unusually well protected against air attacks. Sixteen five-inch high angle guns were mounted in pairs, four mounts to each side of the ship. Although it was planned to mount 115 25-mm. AA- machine-guns, Shinano sailed from Yokosuka with 140 of them bristling from all sides. Of these, 69 were mounted in triple mounts, while the remainder were stationed about the ship in double and single mounts.

As an after-thought, 12 multiple rocket launchers in twin mounts were installed for additional protection. Each launcher was capable of firing 28 or 30 4.7-inch rockets in one salvo. It is interesting to note that the basic idea for Shinano’s rocket launchers was derived from a photograph published in a popular American magazine. According to one Japanese designer,⁸ close examination of the photograph revealed a similar rocket launcher mounted on an allied warship entering an American east coast port. Using this as a lead, a Japanese naval rocket launcher was developed, but too late for extensive World War II use.

Comparative Characteristics of Selected Carriers*†
Aircraft carrier	Standard Displ.	Full load Displ.	Length (ft.)	Beam (ft.)	Draught (ft.)	Speed (kts.)	S.H.P.	Aircraft Capacity	Notes:	Complement
Shinano	68,059	71,890	839.6 w/l	119 max.	33.8 mean	27	150,000	42-47	Sunk, 29-11-44 860-ft., o/a	2,400
Taiho	28,564		829.8 w/l	90.8 max.	31.2 mean	33.3	160,000	68	Sunk, 19-6-44
Shokaku	25,625		820 w/l	86.2 max.	29 mean	34	160,000	96	Sunk, 196-6-44
J.V. Forrestal	59,900+		1,040 o/a	252 max
Midway	45,000	60,000	958 o/a	135 hl. max.	32.7	33	212,000	137		3,000 plus
Oriskany	30,800	39,800	888 o/a	129 hl. max.	30.5 max.		150,000	100	Improved Essex	1,650 peace
Essex	227,100	33,000	876-888 o/a	147 max.	30 max.		150,000	82-90		2,500 war
Ark Royal	36,000	46,000	803.7 o/a	112.7	33.2	31.5	167,000	80-110	HMS Eagle	2,750
*Japanese statistics from Shizen, August, 1950, p. 95; in everything except standard displacement Shizen agrees with the Second Demobilization bureau’s “General Description of the Shinano”
†American and British characteristics from Janes Fighting Ships, 1951-52 edition.

 

Compared to other Japanese aircraft carriers of the war, Shinano was slow; but not too slow for the job she was designed to do. Her four steam turbines developed 150,000 shaft horsepower and were capable of sending the big carrier through the water at the same speed as Yamato and Musashi, about 27-knots. Shinano’s tactical radius was greater than that of the super-dreadnoughts: 10,000 nautical miles at 18-knots.

The above table gives some of the significant dimensions and weights of Shinano and contrasts them with the characteristics of American and British carrier types.

The End—November 29, 1944

Conceived as a compromise and constructed with fervor and purpose, Shinano was rushed to a sudden end by an early, almost premature, launching. Up to the time of the Marianas operation, Shinano was expected to be finished by the spring of 1945. But the June 19th Marianas “Turkey Shoot” was accompanied by the sinking of two of the Imperial Navy’s finest carriers, Taiho and Shokaku, and resulted in reintensified activity at Dry Dock 6 in Yokosuka. Leyte Gulf carrier losses and the further decimation of the Japanese Navy came as added reminders that Shinano’s construction must be finished to help fill the gaps in the rapidly crumbling line of defense.

Shinano was launched on November 11, 1944, and commissioned eight days later. A well-known officer commanded the new carrier and its 1,400-man crew during the brief shake-down in Tokyo Bay. Captain Toshio Abe was faced with the problem of getting his huge ship and the largely untrained and inexperienced crew into fighting condition within two weeks. In late 1944 Tokyo Bay was no place to train a green crew and qualify pilots. Abe was therefore ordered to take Shinano to Kure, where he was to pick up the air complement for Inland Sea exercises.

The yet unfinished carrier sailed from Yokosuka at 1800, November 28th, with yard workers still hard at work aboard. Destroyers Hamakaze, Isokaze and Yukikaze escorted Shinano as she sailed into Tokyo Bay on her maiden voyage, “a half moon shimmering on the waves.”

Meanwhile, the American submarine Archerfish, released from B-29 lifeguard duties for the night, moved in to play the final role in Shinano’s discouraging drama. Looking for Japanese shipping in the Tokyo Bay area, Commander J. F. Enright, skipper of the Archerfish, picked up Shinano on radar while running surfaced late in the evening. Commander Enright maneuvered his boat in for the kill, waiting patiently for Shinano and escorts to cross his firing line. At 0317 a spread of six “steam” torpedoes, set to run at ten-feet, were fired at the unwary carrier. Four of them struck home a minute later. As destroyers maneuvered in to contact Archerfish, the submarine evaded, confident she had dealt a mortal blow to a Shokaku-class aircraft carrier. And Shinano began her death throes, which were to last until late the following morning.

A Japanese naval board of investigation, convened to probe the Shinano disaster later that winter, brought out the facts of what occurred during the carrier’s last seven hours afloat.⁹ Although hit in the stern with four torpedoes, Captain Abe did not reveal any great anxiety over Shinano’s wounds. In fact, the Captain, confident Shinano was, like her sisters had been, almost invulnerable, ordered speed kept at 18-knots over the rough seas.

In the damage control parties working below, however, it soon became apparent that Shinano was in serious trouble. Due to the ship’s hasty construction, water-tight doors had not yet been fitted to some of the threatened compartments. Moreover, as the ship churned through the seas at 18-knots water made considerable headway in penetrating other parts of the ship below the waterline. The green damage control crews, hastily recruited for carrier duty from the bottom of the man-power barrel, could not keep the water back. It soon became apparent that the Counter-flooding pipes were not capable of evenly distributing weight. This was a design deficiency overlooked during the frenzied post-Saipan construction at Yokosuka, and helped bring Shinano’s career to a quick conclusion.

Apprised of developments below, Captain Abe reduced Shinano’s speed. But it was too late. The sea had the upper hand now. At 1018, after listing to a precarious angle, Abe ordered abandon ship, then retired to his cabin to join his ancestors. A few minutes later Shinano capsized and with half her crew she settled noisily into the sea.

If there was any hope left for an ultimate victory of the Empire, that hope settled to the bottom of the Pacific with Shinano on this cold November morning. For those who had watched the great ship grow, from its conception as a dreadnought through its wartime conversion after Midway, the war was indeed over.

As Toshikazu Kase was to say much later in the postscript to his book, Journey to the Missouri, Shinano’s disaster was symbolic of Japan’s war effort. He wrote:

We built a fine ship and took much pride in her. She looked like a majestic and unperishable castle of the seas. But she was sunk before she fired a shot. There is more than a touch of irony in the fate of the Shinano. For a poor country like Japan the construction of costly warships meant a crushing burden upon the national treasury. And yet we built a good number of them. We also maintained a vast Army and an ever expanding Air Force. In the end we became like the mammoth whose tusks, growing ever bigger, finally unbalanced its bodily structure. As everything went to support the huge tusks, very little was left to sustain the rest of the body. The mammoth finally became extinct. . . . The Shinano was indeed a child of misfortune and her fate symbolic of the tragic decade just now dosed with our capitulation.