was an aircraft carrier built by the Imperial Japanese Navy (IJN) during World War II, the largest such built up to that time. Laid down in May 1940 as the third of the s, Shinanos partially complete hull was ordered to be converted to an aircraft carrier following Japan's disastrous loss of four of its original six fleet carriers at the Battle of Midway in mid-1942. The advanced state of her construction prevented her conversion into a fleet carrier, so the IJN decided to convert her into a carrier that supported other carriers.
Her conversion was still not finished in November 1944 when she was ordered to sail from the Yokosuka Naval Arsenal to Kure Naval Base to complete fitting out and transfer a load of 50 Yokosuka MXY7 Ohka rocket-propelled kamikaze flying bombs. She was sunk en route, 10 days after commissioning, on 29 November 1944, by four torpedoes from the U.S. Navy submarine . Over a thousand sailors and civilians were rescued and 1,435 were lost, including her captain. She remains the largest ship ever sunk by a submarine.Enright & Ryan, p. xiv
Design and description
One of two additional Yamato-class battleships ordered as part of the 4th Naval Armaments Supplement Program of 1939,Enright & Ryan, p. 2 Shinano was named after the old province of Shinano, following the Japanese ship-naming conventions for battleships.Silverstone, p. 336 She was laid down on 4 May 1940 at the Yokosuka Naval Arsenal to a modified Yamato-class design: her armor would be thinner than that of the earlier ships, as it had proved to be thicker than it needed to be for the desired level of protection, and her heavy anti-aircraft (AA) guns would be the new 65-caliber 10 cm Type 98 dual-purpose gun, as it had superior ballistic characteristics and a higher rate of fire than the 40-caliber 12.7 cm Type 89 guns used by her half-sisters.Garzke & Dulin, pp. 74–75
Construction and conversion As with Shinanos half-sisters and , the new ship's existence was kept a closely guarded secret. A tall fence was erected on three sides of the graving dock, and those working on the conversion were confined to the yard compound. Serious punishment—up to and including death—awaited any worker who mentioned the new ship. As a result, Shinano was the only major warship built in the 20th century that was never officially photographed during its construction. The ship is only known to have been photographed on three occasions. The first photograph, taken by a Japanese aircraft in mid-October 1944, was intended to review the camouflage efforts made to conceal the carrier while in drydock. Later, on 1 November 1944, a Boeing B-29 Superfortress reconnaissance aircraft captured Shinano near the entrance of Yokosuka Harbor from an altitude of . Ten days later a civilian photographer aboard a harbor tug photographed Shinanos initial sea trials in Tokyo Bay.
In December 1941, construction on Shinanos hull was temporarily suspended to allow the IJN time to decide what to do with the ship. She was not expected to be completed until 1945, and the sinking of the British capital ships and by IJN bombers had called into question the viability of battleships in the war. The navy also wanted to make the large drydock in which the ship was being built available, which required either scrapping the portion already completed or finishing it enough to launch it and clear the drydock. The IJN decided on the latter, albeit with a reduced work force which was expected to be able to launch the ship in one year.Garzke & Dulin, p. 75
In the month following the disastrous loss of four fleet carriers at the June 1942 Battle of Midway, the IJN ordered the ship's unfinished hull converted into an aircraft carrier. Her hull was only 45 percent complete by that time, with structural work complete up to the lower deck and most of her machinery installed. The main deck, lower side armor, and upper side armor around the ship's magazines had been completely installed, and the forward barbettes for the main guns were also nearly finished. The navy decided that Shinano would become a heavily armored support carrierGarzke & Dulin, p. 78—carrying reserve aircraft, fuel and ordnance in support of other carriers—rather than a fleet carrier.Chesneau, p. 185
As completed, Shinano had a length of overall, a beam of and a draft of . She displaced at standard load, at normal load and at full load. Shinano was the heaviest aircraft carrier yet built, a record she held until the was launched in 1954. She was designed for a crew of 2,400 officers and enlisted men.Jentschura, Jung & Mickel, p. 55Preston, p. 91
Machinery Shinanos machinery was identical to that of her half-sisters. The ships were fitted with four geared steam turbine sets with a total of , each driving one propeller shaft, using steam provided by 12 Kampon water-tube boilers. The ships had a designed speed of , but Shinano never conducted full-speed sea trials so her actual performance is unknown.Brown, pp. 32–33 She carried of fuel oil which gave her an estimated range of at .
Flight deck and hangar Shinano was designed to load and fuel her aircraft on deck where it was safer for the ship; experiences in the Battles of Midway and the Coral Sea had demonstrated that the existing doctrine of fueling and arming their aircraft below decks was a real danger to the carriers if they were attacked while doing so. Much of Shinanos hangar was left open for better ventilation, although steel shutters could close off most of the hangar sides if necessary. This also allowed ordnance or burning aircraft to be jettisoned into the sea, something that the earlier carriers could not do with their enclosed hangars.
The carrier's flight deck was wide and overhung her hull at both ends, supported by pairs of pillars. A large island, modeled on that fitted on the earlier , was sponsoned off the starboard side and integrated with the ship's funnel. Much like Taihō, the only other Japanese carrier with an armored flight deck, Shinanos flight deck functioned as the ship's strength deck and copied British practice as seen in their carriers. Designed to resist penetration by bombs dropped by a dive bomber, the flight deck consisted of of armor plate laid over of ordinary steel. It was equipped with 15 transverse arrestor wires and three crash barriers that could stop a aircraft;Brown, p. 32 five of these wires were positioned further forward to allow the ship to land aircraft over the bow in case the aft portion of the flight deck was unusable.
Unlike the British carriers, Taihō and Shinano had unarmored sides to their hangars. For stability reasons, the latter only had a single hangar that was , with a minimum width of aft, and had a height of . The forward area of the hangar was dedicated to maintenance and storage facilities. Aircraft were transported between the hangar and the flight deck by two elevators, one at each end of the hangar on the centerline of the flight deck. The larger of the two measured . They were capable of lifting aircraft weighing up to . The ship had an aviation gasoline (avgas) capacity of . Because Taihō had been sunk by an explosion of gasoline fumes, large ventilation fans were installed on the hangar deck to expel fumes in case of damage to the gasoline system. Canvas wind scoops could also be rigged over the elevator opening to force more air inside.
The ship's organic air group was intended to consist of 18 Mitsubishi A7M Reppū (Allied reporting name "Sam") fighters (plus two in storage), 18 Aichi B7A Ryusei ("Grace") torpedo-dive bombers (plus two in storage), and 6 Nakajima C6N Saiun ("Myrt") reconnaissance aircraft (plus one in storage). The remainder of the hangar space would have held up to 120 replacement aircraft for other carriers and land bases. The steel flight deck was covered with a thin, shock-absorbent latex-sawdust compound.
Armament Shinanos primary armament consisted of sixteen 40-caliber Type 89 dual-purpose guns in eight twin mounts, two at each corner of the hull. When firing at surface targets, the guns had a range of ; they had a maximum ceiling of at their maximum elevation of 90 degrees. Their maximum rate of fire was 14 rounds a minute; their sustained rate of fire was around eight rounds per minute.Campbell, pp. 192–193
The ship also carried 105 Type 96 25 mm (1 in) light AA guns in 35 triple-gun mounts.Garzke & Dulin, p. 79 These guns had an effective range of , and an effective ceiling of at an elevation of +85 degrees. The maximum effective rate of fire was only between 110 and 120 rounds per minute because of the frequent need to change the fifteen-round magazines.Campbell, p. 200 This was the standard Japanese light AA gun during World War II, but it suffered from severe design shortcomings that rendered it largely ineffective. According to historian Mark Stille, the weapon had many faults including an inability to "handle high-speed targets because it could not be trained or elevated fast enough by either hand or power, its sights were inadequate for high-speed targets, it possessed excessive vibration and muzzle blast"....Stille, p. 51 These guns were supplemented by a dozen 28-round AA rocket launchers. Each rocket weighed and had a maximum velocity of . Their maximum range was .Campbell, p. 216
Four Type 94 high-angle fire-control directors were fitted to control the Type 89 guns. The two controlling the port-side guns were adjacent to their guns while the starboard directors were mounted fore and aft on the island. They could control all of the forward and rear guns respectively as necessary. Type 22 and Type 13 air search radars may have been fitted.
Armor The ship's original waterline armor belt thickness of was retained only where it had already been installed abreast the magazines, and reduced to elsewhere. Below it was a strake of armor that tapered in thickness from to 75 millimeters at its bottom edge. The flat portion of the armor deck over the machinery and magazine spaces, ranging from , was retained, and the sloped portion that angled downward towards the bottom of the main armor belt was thick. Large external anti-torpedo bulges below the waterline provided the main defense against torpedoes, backed up by an armored bulkhead extending down from the belt armor; the bulkhead was intended to prevent splinters from piercing the main hull and, though not watertight, was backed by a second one which was. The joint between the upper and lower armor belts was weak and proved to be a serious problem when struck by torpedoes.Garzke & Dulin, pp. 79–80
Even though Shinanos avgas tanks were protected by armor that could resist a shell, the IJN attempted to isolate the tanks from the rest of the ship with a cofferdam. However the investigation into the loss of Taihō had revealed that her avgas tanks had sprung leaks after she was torpedoed. The resulting fumes then penetrated the cofferdam and exploded. Therefore, the IJN thought it prudent to fill the empty spaces between the tanks and the cofferdam with of concrete to prevent any fumes from escaping.
Launching
The ship was originally scheduled for completion in April 1945, but construction was expedited after the defeat at the Battle of the Philippine Sea in June 1944 as the IJN anticipated that the United States would now be able to bomb Japan with long-range aircraft from bases in the Mariana Islands. The builder was unable to increase the number of workers on Shinano and could not meet the new deadline of October. Therefore, the pressure to finish as quickly as possible led to poor workmanship by the workforce.Garzke & Dulin, p. 80