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The Yokosuka-built Aircraft Carrier Shinano

10 June 2022

From Ryo Isobe

Most of the story of Shinano, an Imperial Japanese Navy (IJN) aircraft carrier during World War II, is only known through a few eye-witness accounts, as the records or photos were scattered or lost after the war. Here is a story from Hosokawa Chiyokichi, who worked as a ship rigger at Ship Repair Facility (SRF) onboard Commander, Fleet Activities Yokosuka (CFAY), recounted in the Sept. 1979 issue of SRF’s newspaper, “Anchor.”
Most of the story of Shinano, an Imperial Japanese Navy (IJN) aircraft carrier during World War II, is only known through a few eye-witness accounts, as the records or photos were scattered or lost after the war. Here is a story from Hosokawa Chiyokichi, who worked as a ship rigger at Ship Repair Facility (SRF) onboard Commander, Fleet Activities Yokosuka (CFAY), recounted in the Sept. 1979 issue of SRF’s newspaper, “Anchor.”

Hosokawa joined the IJN and finished the Yokosuka Naval Recruiting Training course in 1937 as a machinist mate apprentice. After graduation, he was assigned to several ships, and promoted to the rank of petty officer as a machinist mate. His last assignment at the IJN was aboard Shinano as a group leader in the #3 Engine Room beginning in early 1944.

IJN aircraft carrier Shinano, which was the largest carrier ever during World War II, was built at Yokosuka Arsenal’s dry dock #6 in 1944. While the other five preceding docks in Yokosuka were built primarily for ship maintenance, dry dock #6 was specifically designed for shipbuilding. With a length of 136.5 meters, a width of 67.5 meters, and a depth of 17 meters, the dock was exclusively planned for building and maintaining Yamato-class battleships. The construction of the dock was commenced in 1935 and completed in 1940, and almost at the same time, Shinano’s keel was laid on May 4, 1940.

Shinano was originally planned as the third Yamato-class battleship. However, the idea that a “major ship for sea battle should be an aircraft carrier instead of a battleship,” was getting stronger among the IJN authorities. Therefore, the ship design was altered, even though the hull construction was almost complete and the ship was ready for the installation of a 46-centimeter gun on the upper deck.

After four years and six months of around-the-clock work, the construction, and modifications were completed in 1944.

The launch, which was originally scheduled for Oct. 8, 1944, was delayed due to an accident involving the ship’s undocking, which resulted in damage to the bow. It was estimated that inexperienced workers and sailors, who had been mobilized for expedited construction of the ship, mishandled the caisson on the dock, causing a sudden rush of water into the dry dock, pushing the ship forward.

“An unexpected flooding accident occurred during the flooding of the dock at the initial launching, which seemed to predict her fate and the coming end of WWII,” said Hosokawa. “After a quick repair of 10 days, she was launched again.”
On Nov. 19, 1944, Shinano was officially commissioned, and on Nov. 28 departed for Kure, Yamaguchi prefecture, where the remainder of the ship-fitting work would take place. Shinano, with escort ships, had only been cruising four hours before they were caught on radar by the Balao-class submarine USS Archerfish (SS 311) and followed through the waters near Tokyo Bay.

Shinano’s escorts included the ships Isokaze, Yukikaze and Hamakaze, which were caught on Archerfish’s radar and followed by the submarine on a parallel course.

Believing that Archerfish was a decoy to lure Shinano into a convoy attack, Capt. Toshio Abe, commanding officer of Shinano, ordered that the ships outrun it by using a zigzag maneuver. However, by midnight, the ships were forced to reduce the speed to prevent the Shinano’s propeller shaft’s bearing from overheating.

Archerfish grabbed the opportunity and submerged in preparation for an attack. Shinano tried to turn southwest but ended up heading straight toward the submarine. Within a matter of minutes, the ship turned south, inadvertently exposing its side, offering an ideal firing situation for the submarine to attack.

At 3:15 a.m. Nov. 29, 1944, Archerfish fired six torpedoes, striking Shinano.

According to Hosokawa, Shinano was hit in the shaft-room of the #3 Engine Room on the starboard side. Upon impact, several thousand rivets on the bulkhead, especially between the shaft room and the engine room, came loose all at once. For IJN ships, rivets were used throughout the hull unlike modernized vessels, which are largely built by welding. The damage got worse with increasing water pressure and was beyond the crews’ ability to correct. Lifeboats and buoys were not available for the crew aboard Shinano, as they believed that, “escape from the ship equals timidity,” recalls Hosokawa.

Shinano was sunk on its maiden voyage 160 nautical miles southwest of Tokyo Bay, going down in history as the largest warship annihilated by any combatant submarine during World War II.

The number of shipyard workers and crew member who were lost with the ship is unknown, but Hosokawa was one of the few sailors and engineers who were rescued and survived from the sinking ship.

The Imperial Japanese Navy believed that the Yamato-class battleships, which were heavily armed with gigantic guns and turrets were the most powerful and unmatchable with the other U.S. Navy’s battleships in the sea battles, however, of all the three ships of the IJN Yamato-class vessels were lost. The second ship, Musashi, was sunk in October of 1944, and the lead ship, Yamato, was also sunk in April of 1945. As mentioned above, the third ship, hastily modified as an aircraft carrier, was Shinano. With its consecutive tragic mishaps, it was a swan song for the age of super-dreadnoughts when the times were weighing more on the strategic value of aircraft carriers.

Even after World War II, CFAY’s dry dock #6 has been continuously used for the U.S. Navy’s ship repair, and it has dry-docked large U.S. Navy ships including USS Midway (CV 41), USS Independence (CV 62), and USS Kitty Hawk (CV 63). Recently dry dock #6 saw a major achievement of a scheduled extended dry dock repair and maintenance period for the 7th Fleet flagship USS Blue Ridge (LCC 19), from 2016 through 2018, upgrading multiple systems, extending the ship’s life by approximately 20-plus years.

CFAY ensures the capability of dry dock #6 in order to keep 7th Fleet ships mobile and ready at all times.

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