Japanese aircraft carrier Shinano

Shinano (信濃), named after the old province of Shinano, was an aircraft carrier built by the Imperial Japanese Navy (IJN) during World War II. Initially laid down as the third of the s, Shinano's partially complete hull was converted to an aircraft carrier in 1942, midway through construction. Over the next two years, the ship was heavily modified and she became the largest aircraft carrier built up to that time.

Partially completed in November 1944, Shinano was sent 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. En route to Kure, she was sunk on 19 November 1944, 10 days after commissioning, by four torpedoes from the American submarine USS Archer-Fish (SS-311). The ship carried an inexperienced crew, had serious design and construction flaws, and was not ready for combat. Over a thousand of her crew and passengers were rescued, but 1,435 sailors and civilians died, including her captain. Shinano remains the largest warship ever sunk by a submarine.

Design and description
One of two additional Yamato-class battleships ordered as part of the 4th Naval Armaments Supplement Program of 1939, Shinano was named after Shinano Province, following the Japanese ship-naming conventions for battleships. She was laid down on 4 May 1940 at the Yokosuka Naval Arsenal to a modified Yamato-class design: her armor would be 10 - 20 mm 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 higher rate of fire than the 40-caliber 12.7 cm Type 89 guns used by her half-sisters.

Construction and conversion
As with Shinano's half-sisters JAPANESE BATTLESHIP Yamato and JAPANESE BATTLESHIP Musashi, 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 to have avoided being officially photographed during its construction. The ship is only known to have been photographed twice: on 1 November 1944, by a Boeing B-29 Superfortress reconnaissance aircraft from an altitude of 32000 ft, and ten days later, by a civilian photographic technician aboard a harbor tug during Shinano's initial sea trials in Tokyo Bay.

In December 1941, construction on Shinano's 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 HMS Prince of Wales (53) and HMS Repulse (1916) 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.

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 carrier —carrying reserve aircraft, fuel and ordnance in support of other carriers—rather than a fleet carrier.

As completed, Shinano had a length of 265.8 m overall, a beam of 36.3 m and a draft of 10.3 m. She displaced 64800 LT at standard load and 68059 LT at normal load. Her crew consisted of 2,400 officers and enlisted men.

Machinery
Shinano's machinery was identical to that of her half-sisters. The ships were fitted with four geared steam turbine sets with a total of 150000 shp, each driving one propeller shaft, using steam provided by 12 Kampon water-tube boilers. The ships had a designed speed of 27 kn, but Shinano never conducted full-speed sea trials so her actual performance is unknown. She carried 8904 LT of fuel oil which gave her an estimated range of 10000 nmi at 18 kn.

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 Shinano's 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 256 m flight deck was 131 ft wide and overhung her superstructure at both ends, supported by pairs of pillars. A large island, modeled on that fitted on JAPANESE AIRCRAFT CARRIER Taihō, was sponsoned off the starboard side and integrated with the ship's funnel. Much like the earlier Taihō design, Shinano's armored flight deck functioned as the ship's strength deck and copied British practice as seen in their carriers. Designed to resist penetration by 500 kg bombs dropped by a dive bomber, the flight deck was 75 mm thick. It was equipped with 15 transverse arrestor wires and three crash barriers that could stop a 7500 kg aircraft; 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 536 by, with a minimum width of 65 ft aft, and had a height of 16 ft. 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 49.25 by. They were capable of lifting aircraft weighing up to 7500 kg. The ship had an aviation gasoline capacity of 720000 l. Large ventilation fans were installed on the hangar deck to expel fumes in case of damage to the gasoline system; Taihō had been sunk by an explosion of gasoline fumes. 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.

Armament
Shinano's primary armament consisted of sixteen 40-caliber 12.7 cm 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 14700 m; they had a maximum ceiling of 9440 m 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.

The ship also carried 105 Type 96 25 mm light AA guns in 35 triple-gun mounts. These 25 mm guns had an effective range of 1500 - 3000 m, and an effective ceiling of 5500 m 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. 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".... These guns were supplemented by a dozen 28-round AA rocket launchers. Each 12 cm rocket weighed 22.5 kg and had a maximum velocity of 200 m/s. Their maximum range was 4800 m.

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 400 mm was only retained where it had already been installed abreast the magazines, and reduced to 160 mm elsewhere. Below it was a strake of armor that tapered in thickness from 200 mm to 75 mm at its bottom edge. The flat portion of the armor deck over the machinery and magazine spaces, ranging from 100 to 190 mm, was retained, and the sloped portion that angled downward towards the bottom of the main armor belt was 230 mm 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 water-tight, 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.

Taihō and Shinano were the only Japanese aircraft carriers with armored flight decks. The latter's flight deck had 75 mm of armor plate laid over 20 mm of ordinary steel.

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 that was supposed to isolate the tanks from the rest of the ship. Even though Shinano's tanks were protected by armor that could resist a 155 mm shell, the IJN thought it prudent to fill the empty spaces between the tanks and cofferdams with 2400 t of cement 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 bombers 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. Even so, the pressure to finish as quickly as possible led to poor workmanship by the workforce.

Shinano's launch on 8 October 1944, with Captain Toshio Abe in command, was marred by what some considered an ill-omened accident. During the floating-out procedure, one of the caissons at the end of the dock unexpectedly lifted as the water rose to the level of the harbor (no one had checked to ensure that all the caissons were properly ballasted with seawater). The sudden inrush of water into the graving dock pushed the carrier into the forward end, damaging the bow structure below the waterline and requiring repairs in drydock. These were completed by 26 October. With a full-load displacement of 72000 LT, Shinano was the largest aircraft carrier yet built, a record she held until the 80000 LT USS Forrestal (CV-59) was launched in 1954.

Commissioning and sinking
On 19 November 1944, Shinano was formally commissioned at Yokosuka, having spent the previous two weeks fitting out and performing sea trials. Worried about her safety after a U.S. reconnaissance bomber fly-over, the Navy General Staff ordered Shinano to depart for Kure by no later than 28 November, where the remainder of her fitting-out would take place. Abe asked for a delay in the sailing date as the majority of her watertight doors had yet to be installed, the compartment air tests had not been conducted, and many holes in the compartment bulkheads for electrical cables, ventilation ducts and pipes had not been sealed. Nor had the fire mains or drainage systems been completed as their pumps had not been delivered and the ship lacked portable submersible pumps. Most of the crew had sea-going experience, but they did not know how to operate the portable pumps on board. The escorting destroyers, Isokaze, Yukikaze and Hamakaze, had just returned from the Battle of Leyte Gulf and required more than three days to conduct repairs and to allow their crews to recuperate.

Abe's request was denied, and Shinano departed as scheduled with the escorting destroyers at 18:00 on 28 November. Abe commanded a crew of 2,175 officers and men. Also on board were 300 shipyard workers and 40 civilian employees. Watertight doors and hatches were left open for ease of access to machinery spaces, as were some manholes in the double and triple-bottomed hull. Abe would have preferred to make the trip in daylight, but the Navy General Staff could not provide air support. Shinano carried six Shinyo suicide boats, and 50 Ohka suicide flying bombs; her aircraft were not planned to come aboard until later. Her orders were to go to Kure, where she would complete fitting out and then deliver the kamikaze craft to the Philippines and Okinawa. Traveling at an average speed of 20 kn, she needed sixteen hours to cover the 300 miles (480 km) to Kure.

At 20:48, the American submarine USS Archer-Fish (SS-311), commanded by Commander Joseph F. Enright, picked up Shinano and her escorts on her radar and pursued them on a parallel course. Over an hour and a half earlier, Shinano had detected the submarine's radar. Normally, Shinano would have been able to outrun Archer-Fish, but the zig-zagging movement of the carrier and her escorts—intended to avoid submarine attack—inadvertently turned the task group back into the sub's path on several occasions. At 22:45, the carrier's lookouts spotted Archer-Fish on the surface and Isokaze broke formation, against orders, to investigate. Abe ordered the destroyer to return to the formation without attacking because he believed that the submarine was part of an American wolfpack and that Archer-Fish was being used as a decoy to lure away one of the escorts to allow the rest of the pack a clear shot at Shinano. He ordered his ships to turn away from the submarine with the expectation of outrunning it, counting on his 2 kn margin of speed over the submarine. Around 23:22, the carrier was forced to reduce speed to 18 kn, the same speed as Archer-Fish, to prevent damage to the propeller shaft when a bearing overheated.

At 02:56 on 29 November, Shinano turned to the southwest and headed straight for Archer-Fish. The submarine submerged eight minutes later in preparation to attack. Enright ordered his torpedoes set for a depth of 10 ft in case they ran deeper than set; he also intended to increase the chances of capsizing the ship by punching holes higher up in the hull. A few minutes later, she turned south, exposing her entire side to the submarine, which was heading due east. The escorting destroyer on that side passed right over Archer-Fish without detecting her. At 03:15 Archer-Fish fired six torpedoes before diving to 400 ft to escape a depth charge attack from the escorts.

The torpedoes ran deep and four of the six torpedoes struck the Shinano at an average depth of 4.27 m. The first torpedo struck Shinano towards the stern, flooding refrigerated storage compartments and one of the empty aviation gasoline storage tanks. The detonation also killed many of the sleeping engineering personnel in the compartments above. The second torpedo hit the compartment where the starboard outboard propeller shaft entered the hull and flooded the outboard engine room. The third torpedo hit further forward, flooding the No. 3 boiler room and killing every man on watch. Structural failures caused the two adjacent boiler rooms to flood as well. The fourth and final torpedo flooded the starboard air compressor room, the adjacent anti-aircraft gun magazines, and No. 2 damage-control station, and ruptured the adjacent oil tank.

The extensive flooding gave the carrier a 10 degree list to starboard within a few minutes. Despite pumping 3000 LT of water into the port bilges, the list increased to 13 degrees. Though severe, the damage to Shinano was at first judged to be manageable, and the carrier continued at full speed. The crew were confident in the ship's armor and its strength, which translated into lax efforts to save the ship initially, and the captain ordered a change of course towards Shiono Point. Progressive flooding increased the list to 15 degrees by 03:30. Fifty minutes later, Abe ordered the empty port outboard tanks to be flooded, reducing the list to 12 degrees for a brief time. After 05:00 he ordered the civilian workers to be transferred to the escorts as they were impeding the crew in their duties.

A half-hour later, Shinano was making 10 knots with a 13 degree list. At 06:00 her list had increased to 20 degrees after the starboard boiler room flooded, at which point the port trimming tanks' valves rose above the waterline and became ineffective. The engines shut down for lack of steam around 07:00 and Abe ordered all of the propulsion compartments evacuated an hour later. He then ordered the three outboard port boiler rooms flooded in a futile attempt to reduce the carrier's list. He also ordered Hamakaze and Isokaze to take her in tow, but the two destroyers only displaced 5000 t between them, barely a fraction of Shinano's displacement and not nearly enough to overcome her deadweight. The first tow cables snapped under the strain and the second attempt was aborted for fear of injury to the crews if they snapped again. The ship lost all power around 09:00 and was now listing over 20 degrees. At 10:18, Abe gave the order to abandon ship; by this time Shinano had a list of 30 degrees. As she heeled her flight deck touched the water, which flowed into the open elevator well, sucking many swimming sailors back into the ship as she sank. A large exhaust vent below the flight deck also sucked many other sailors into the ship as it submerged.

At 10:57 Shinano finally capsized and sank stern-first at coordinates (32.11667°N, 137.06667°W), 65 mi from the nearest land, in approximately 4000 m of water, taking 1,435 officers enlisted men and civilians to their deaths, including Abe, who chose to go down with his ship. Rescued were 55 officers and 993 petty officers and enlisted men, plus 32 civilians for a total of 1,080 survivors. The survivors were isolated on the island of Mitsuko-jima until January 1945 after their rescue to suppress the news of the carrier's loss. The carrier was formally struck from the Naval Register on 31 August.

Post-war analysis of the sinking
Post-war analysis by the U.S. Naval Technical Mission to Japan noted that Shinano had serious design flaws. Specifically, the joint between the waterline armor belt on the upper hull and the anti-torpedo bulge on the underwater portion was poorly designed; Archer-Fish's torpedoes all exploded along this joint. The force of the torpedo explosions also dislodged an H-beam in one of the boiler rooms which punched a hole into another boiler room. In addition, the failure to test for water-tightness in each compartment played a role as potential leaks could not be found and patched before Shinano put to sea. Abe's decision to maintain full speed forced more water through the holes in the hull and put more pressure on interior bulkheads, many of which leaked or failed. The executive officer blamed the large amount of water that entered the ship on the failure to air-test the compartments for leaks.