Japanese aircraft carrier Shinano

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.

Design and description

thumb|Drawing of the Shinano as she appeared on 19 November 1944

One of two additional Yamato-class battleships ordered as part of the 4th Naval Armaments Supplement Program of 1939, Shinano was named after the old province of Shinano, 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 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.

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 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 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.

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. She carried of fuel oil which gave her an estimated range of at . 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.

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.

The ship also carried 105 Type 96 25 mm (1 in) light AA guns in 35 triple-gun mounts. 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. 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.

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.

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.

Shinanos launch on 8 October 1944, with Captain 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 that had not been properly ballasted with seawater unexpectedly lifted as the water rose to the level of the harbor. 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. Worried about her safety after the fly-over, they lacked training in the portable pumps on board. He was also concerned for the crews of the escorting destroyers, , and . The destroyers 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 preferred a daylight passage, since it would have allowed him extra time to train his crew and given the destroyer crews time to rest. However, he was forced to make a nighttime run when he learned the Navy General Staff could not provide air support. Shinano carried six Shinyo suicide boats, and 50 Ohka suicide flying bombs;

Attacked

thumb|left|Archerfish on the surface, June 1945

At 20:48, the American submarine , commanded by Commander Joseph F. Enright, detected 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 Archerfish, but the zig-zagging movement of the carrier and her escorts—intended to evade any American submarines in the area—inadvertently turned the task group back into the Archerfishs path on several occasions. At 22:45, the carrier's lookouts spotted Archerfish 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. He assumed Archerfish 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 margin of speed over the submarine. Around 23:22, the carrier was forced to reduce speed to , the same speed as Archerfish, 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 Archerfish. Eight minutes later, Archerfish turned east and submerged in preparation to attack. A few minutes later, Shinano turned south, exposing her entire side to Archerfish—a nearly ideal firing situation for a submarine. The escorting destroyer on that side passed right over Archerfish without detecting her. At 03:15 Archerfish fired six torpedoes before diving to to escape a depth charge attack from the escorts. Enright set his torpedoes to run shallow, at a depth of . He not only wanted to ensure they would hit if they ran deeper than set, but also hoped to increase the chances of capsizing the ship by punching holes higher up in the hull.

Four torpedoes struck Shinano, at an average depth of .

Sinking

thumb|upright=1.4|Diagram showing locations of torpedo hits and ensuing flooding: Red shows compartments immediately flooded, orange slowly flooded, and yellow deliberate flooding to offset the ship's list

Though severe, the damage to Shinano was at first judged to be manageable. This pushed more water through the holes in the hull resulting in extensive flooding. Within a few minutes the ship was listing 10 degrees to starboard. Despite the crew pumping of water into the port bilges, the list increased to 13 degrees. When it became apparent the damage was more severe than first thought, Abe ordered a change of course towards Shiono Point, the southernmost tip of Honshu's Kii Peninsula. Progressively increasing flooding increased the list to 15 degrees by 03:30. Fifty minutes later, Abe ordered the empty port outboard tanks to be counter-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 valves of the port trimming tanks 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. However, the two destroyers displaced only between them, about one-fourteenth of Shinanos 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. While Abe refused to issue any formal orders to abandon ship, at 10:18 he realized the situation was untenable and released the crew to save themselves. At this time Shinano had a list of 30 degrees. As she heeled, water flowed into the open elevator well on her flight deck, 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 she submerged.

At 10:57 Shinano finally capsized and sank stern-first at coordinates (), from the nearest land, in approximately of water, taking 1,435 officers, men and civilians to their deaths. The dead included Abe and both of his navigators, who chose to go down with the ship. Rescued were 55 officers and 993 petty officers and enlisted men, plus 32 civilians for a total of 1,080 survivors. The carrier was formally struck from the Naval Register on 31 August. even though a captured Japanese aviator had revealed in July 1943 that a third Yamato-class battleship was being converted into a carrier. Enright was eventually credited with sinking a Hayatake () carrier by the acting commander of the Pacific Fleet's submarine force on the basis of a drawing Enright submitted depicting the ship he had attacked. Once the existence of Shinano was discovered, Enright was credited with her sinking and awarded the Navy Cross. The executive officer blamed the large amount of water that entered the ship on the failure to air-test the compartments for leaks. He reported hearing air rushing through gaps in the watertight doors just minutes after the last torpedo hit—a sign that seawater was rapidly entering the ship, proving the doors were unseaworthy.

Footnotes

References

External links

Two plans of the ship have been located in the National Archives and Records Administration files and are available for download at [https://catalog.archives.gov/id/76028759] and [https://catalog.archives.gov/id/76028757] .