During World War II, the Imperial Japanese Navy (IJN) built many remarkable warships, with the IJN Shinano standing out as particularly notable. Originally intended to be a Yamato-class battleship, Japan’s losses at the Battle of Midway led to a strategic change, converting her into an aircraft carrier instead.
Shinano holds historical significance as the largest warship ever lost to a submarine.
Construction of the IJN Shinano
Construction of the IJN Shinano began on May 4, 1940, at the Yokosuka Naval Arsenal and continued steadily until 1942. That year, however, a series of strategic defeats to American forces prompted a change in plans, leading to her conversion from a battleship into an aircraft carrier. Instead of becoming a fleet carrier, Shinano was reimagined as a heavily armored support carrier with a displacement of 65,800 tons, primarily intended for storing reserve aircraft and fuel.
Shinano’s construction was shrouded in secrecy, with a tall fence erected around the site to block any external view. Workers were required to adhere to strict confidentiality agreements, with severe penalties, including execution, for any breaches.
Consequently, Shinano is the only major warship of the 20th century for which no construction photographs are known to exist. Even after her completion, she was photographed only twice: once by a Boeing B-29 Superfortress on a reconnaissance mission and once by a civilian during her sea trials.
Armor and armament
The IJN Shinano was designed based on the design of the Yamato and Musashi. Originally, she was planned to have slightly thinner armor, reduced by 10-20 mm, and more modern anti-aircraft guns. However, these plans were altered when she was converted into an aircraft carrier. This transformation resulted in significant departures from the Yamato-class, with Shinano losing much of her armor and large main guns.
As a carrier, Shinano featured the characteristic flat top for her role, with a smooth and streamlined flight deck. She was enormous, measuring 872 feet in length, with a beam of 119 feet and a draft of nearly 34 feet. Her propulsion system consisted of 12 Kampon water boilers driving four steam turbines. This arrangement produced 150,000 shaft horsepower, enabling Shinano to reach a top speed of 27-28 knots under optimal conditions.
Shinano was designed to accommodate a large number of aircraft and was well-defended for her time. She was outfitted with 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. Her waterline armor ranged from 160-400 mm in thickness, while her flight deck had 75 mm of armor.
Traveling toward certain destruction
Initially planned for commissioning in early 1945, the IJN Shinano‘s construction timeline was accelerated following the Battle of the Philippine Sea. This battle inflicted heavy losses on the Japanese Navy, including the destruction of two fleet carriers, one light carrier, and two oilers, while several smaller vessels sustained damage.
The hastened construction of Shinano led to compromised workmanship on later components. Nevertheless, she was launched on October 8, 1944, and officially commissioned on November 19 of the same year.
After her commissioning, Shinano was scheduled to travel from the shipyard to Kure Naval Base, where she was to be outfitted with armaments and aircraft under the command of Capt. Toshio Abe. Although Abe requested a delay due to incomplete bailing pumps and fire mains, his superiors denied his appeal and insisted on immediate departure. As a result, he was forced to set sail at night, despite his preference for a daytime departure.
Shinano departed at 6:00 PM on November 28, 1944, escorted by Isokaze, Yukikaze, and Hamakaze. During the voyage, the group detected radar signals indicating the presence of an American submarine nearby, prompting evasive maneuvers. Unknowingly, these actions placed Shinano directly in the path of the USS Archerfish (SS-311).
Sinking of the IJN Shinano
Joseph Enright, commanding the USS Archerfish, detected the IJN Shinano two hours before the aircraft carrier became aware of the submarine’s presence. Mistaking the vessel for part of an American wolfpack, Cmdr. Abe of the Japanese forces ordered his ships to change course to evade Archerfish. Despite Shinano‘s superior speed, she was required to slow down to avoid any likely damage.
At 2:56 AM on November 29, Abe initially steered toward the submarine, but then veered southwest, inadvertently exposing Shinano‘s entire flank to Archerfish. At 3:15 AM, Enright ordered the launch of six torpedoes, two of which struck their target before the submarine dove to a depth of 400 feet to avoid counterattack.
Shinano was hit by four torpedoes, leading to her sinking. Enright and his crew didn’t learn the carrier’s identity until the end of World War II and were unaware that it took over seven hours for the Japanese vessel to sink after being struck.
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.
Are you a fan of all things ships and submarines? If so, subscribe to our Daily Warships newsletter!
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.
Leave a Comment