During World War II, the Imperial Japanese Navy (IJN) built numerous notable warships, with the IJN Shinano being particularly noteworthy. Originally planned as a Yamato-class battleship, changes in strategy led to its conversion into an aircraft carrier, a decision influenced by substantial losses suffered by the Japanese fleet in the Battle of Midway.
Shinano is famous for its distinctive historical significance, notably as the largest warship ever sunk by a submarine attack.
Construction of the IJN Shinano
Construction on the IJN Shinano started on May 4, 1940, at the Yokosuka Naval Arsenal, progressing smoothly until a key moment in 1942 when it was repurposed from a battleship to an aircraft carrier due to Japan’s setbacks against the Americans.
Instead of serving as a fleet carrier, Shinano underwent conversion into a heavily armored support carrier, boasting a displacement of 65,800 tons, primarily intended for storing reserve aircraft and fuel.
The construction of Shinano was shrouded in utmost secrecy, with a high fence surrounding the building site to keep it concealed from public view. Workers were bound by strict confidentiality, facing severe consequences, including execution, for any breaches.
Consequently, Shinano stands out as the sole major warship of the 20th century for which no construction photographs exist. Even after it was finished, the ship was filmed only twice: once by a Boeing B-29 Superfortress during reconnaissance and once by a civilian during sea trials.
Armor and armament
The IJN Shinano underwent modifications influenced by the design of the design of the Yamato and Musashi. Originally planned to have slightly thinner armor by 10-20 mm and fitted with newer anti-aircraft guns, these specifications were altered when she was repurposed into an aircraft carrier. Consequently, Shinano diverged significantly from the typical appearance of a Yamato-class ship, shedding a considerable portion of her armor and large main guns.
In her new form, Shinano took on the characteristic flat top of aircraft carriers and a streamlined flight deck.
Shinano boasted impressive dimensions, measuring 872 feet in length, with a beam of 119 feet and a draught of nearly 34 feet. Her power source consisted of 12 Kampon water boilers, driving four geared steam turbines, which in turn propelled an equal number of shafts, producing 150,000 shaft horsepower. Under optimal conditions, this setup enabled the aircraft carrier to achieve a surface speed of approximately 27-28 knots.
Designed to accommodate a diverse range of aircraft, Shinano was considered defensively robust among carriers. It featured eight twin five-inch dual-purpose guns, 35 triple one-inch anti-aircraft guns, and twelve 28-barrel 4.7-inch anti-aircraft rocket launchers. Along the waterline, Shinano’s armor ranged from 160-400 mm in thickness, while the flight deck boasted 75 mm of armor.
Traveling toward certain destruction
Initially slated for commissioning in early 1945, the construction schedulefor the IJN Shinano was expedited following the Battle of the Philippine Sea. The engagement inflicted major losses on the Japanese Navy, including two fleet carriers, one light carrier and two oilers, with several smaller vessels sustaining damage.
The accelerated construction of Shinano resulted in compromised workmanship on later components. Despite this, she was launched on October 8, 1944, and commissioned on November 19 of the same year.
Following her commissioning, Shinano was scheduled to transit from her shipyard to Kure Naval Base, where she’d be armed and receive aircraft under the command of Capt. Toshio Abe. Despite pressure from superiors to depart immediately, Abe requested a delay, due to incomplete bailing pumps and fire mains. Unfortunately, his plea was denied, and he was forced to set sail at night, contrary to his preference for a daytime departure.
Leaving at 6:00 PM on November 28, 1944, Shinano was accompanied by Isokaze, Yukikaze and Hamakaze. While en route, the ships detected radar signals that indicated the presence of an American submarine nearby, prompting them to employ evasive maneuvers. Unbeknownst to the crew, these inadvertently placed Shinano directly in the path of the USS Archerfish (SS-311).
Sinking of the IJN Shinano
Cmdr. Joseph Enright, aboard the USS Archerfish, had detected the IJN Shinano two hours prior to the Japanese aircraft carrier noticing the submarine’s presence. Believing they were encountering an American wolfpack, Abe, the Japanese commander, ordered his ships to steer away from the Archerfish in a bid to outpace the submersible. Although Shinano was faster than the Archerfish, the former had to reduce speed to avoid potential damage.
By 2:56 AM on November 29, Abe altered course to approach the submarine, but subsequently changed direction southwestward, inadvertently exposing Shinano’s entire flank to the Archerfish. At 3:15 AM, Enright authorized the decision to fire six torpedoes, two of which struck the target before the submarine dived to a depth of 400 feet to evade retaliation.
The Shinano was hit by four torpedoes, which was enough to sink her. Enright and his crew remained unaware of their target’s identity until the conclusion of the Second World War, and were oblivious to the fact that it took over seven hours for the aircraft carrier to succumb to its fate.
Hindsight is 20/20
Initially, those aboard the IJN Shinano underestimated the severity of the damage caused by the torpedo strikes, meaning minimal effort was made to salvage the ship. Abe, in particular, directed her to maintain maximum speed, inadvertently accelerating the flooding of the aircraft carrier.
Unfortunately, by the time they grasped the gravity of the situation, it was too late. The ship had become too heavy to be towed by escort vessels, too inundated to be pumped out and too irreparably damaged for the majority of her crew to evacuate. Out of her 2,400-man crew, 1,435 perished with the ship, including Abe and both navigators.
The survivors were sent to Mitsukejima until January of the subsequent year, preventing the widespread dissemination of news about Shinano‘s sinking. Following the conclusion of the war, the US Navy analyzed the aircraft carrier, along with other Yamato-class ships, and identified significant design flaws that rendered specific joints susceptible to leakage. It was concluded that the torpedoes from the USS Archerfish happened to strike these vulnerable joints, contributing to Shinano‘s demise.
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Regarding Enright, US Naval Intelligence initially doubted his claim of sinking a Japanese carrier, believing all had been identified. However, this was rectified after the war, and Enright was duly honored with the Navy Cross for his victorious achievement.