During World War II, the Imperial Japanese Navy launched an ambitious shipbuilding program that included some of the largest warships ever built. Japanese aircraft carrier Shinano was originally laid down as the third Yamato-class battleship, part of the class that produced the largest battleships ever constructed. After Japan’s defeat at the Battle of Midway, naval strategy shifted toward aircraft carriers, and Shinano was converted into a carrier while still being built.
Even with her enormous size and heavy armor, Shinano had an extremely short service life. Soon after entering service, she was torpedoed and sunk by USS Archerfish (SS-311). Her loss made her the largest warship ever sunk by a submarine, giving her a dramatic and lasting place in naval history.
Construction of the IJN Shinano
Construction of the Japanese aircraft carrier Shinano began on May 4, 1940, at the Yokosuka Naval Arsenal. She was originally laid down as the third vessel of the formidable Yamato-class battleships. Following Japan’s heavy wartime losses, particularly after the Battle of Midway, the Imperial Japanese Navy changed course before the ship was completed. The unfinished battleship was converted into a 65,800-ton support aircraft carrier designed to provide other carrier groups with aircraft, fuel, and ammunition rather than serve as a frontline combat carrier.
Security measures surrounding Shinano‘s construction were extraordinarily tight. The shipyard was hidden behind tall fences, guarded under strict security, and anyone responsible for leaking information faced severe penalties. Because of these precautions, no verified photographs of the ship during construction are known to exist. Today, only two authenticated images of Shinano survive: one captured by a B-29 Superfortress during a reconnaissance flight and another taken by a civilian while the carrier was undergoing her brief sea trials.
Armor and armament
The IJN Shinano was initially based on the design of the Yamato and Musashi, with plans calling for slightly thinner armor and upgraded anti-aircraft capabilities. However, once she was converted from a battleship into an aircraft carrier, her design shifted significantly. Much of her original armor and her massive main guns were sacrificed to accommodate her new role.
As a carrier, Shinano featured a large, flat flight deck with a smooth, modern profile. She was massive—872 feet long, 119 feet wide at the beam, and had a draft of nearly 34 feet. Her power came from 12 Kampon water-tube boilers connected to four steam turbines, producing a total of 150,000 shaft horsepower. This gave her an impressive top speed of 27 to 28 knots under ideal conditions.
Shinano was built to carry a significant number of aircraft and defend herself with an array of weaponry. Her defenses included eight twin-mounted 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 to 400 mm thick, and her flight deck was protected by 75 mm of armor—making her one of the most heavily armored carriers of her time.
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, the captain of the USS Archerfish, spotted the Japanese aircraft carrier IJN Shinano two hours before the carrier realized a submarine was nearby. Commander Abe, in charge of the Japanese forces, mistakenly thought they were dealing with a group of American submarines and ordered his ships to change course to escape. Even though Shinano was the faster ship, it had to slow down to avoid possible damage.
At 2:56 AM on November 29, Abe first steered his ship toward the submarine but then turned southwest, unintentionally exposing Shinano’s entire side to Archerfish. At 3:15 AM, Enright ordered the launch of six torpedoes. Two of them struck the carrier before the submarine quickly dove to a depth of 400 feet to avoid any counterattack.
In total, Shinano was hit by four torpedoes, leading to her sinking. Enright and his crew didn’t learn the true identity of the carrier until after World War II. They also didn’t know that it took more than seven hours for Shinano to go under after being hit.
Hindsight is 20/20
At first, the crew aboard the Japanese aircraft carrier Shinano did not fully understand how serious the torpedo damage was, so only limited efforts were made to save the ship. Commander Abe, especially, insisted on keeping the ship at full speed, which unintentionally made the flooding worse and caused Shinano to sink faster.
By the time the crew realized how severe the damage was, it was too late to save the ship. Shinano had become too heavy to tow, too flooded to pump out, and too badly damaged for many of the crew to escape. Of the roughly 2,400 men on board, 1,435 perished with the ship, including Abe and both of his navigators.
The survivors were taken to Mitsukejima and kept there until January of the following year to prevent news of the sinking from spreading widely. After the war, U.S. Navy analysis found major design weaknesses in the Yamato-class ships, especially in joints that were vulnerable to leaking. Investigators concluded that the torpedoes fired by USS Archerfish (SS-311) struck these weak points, directly contributing to the carrier’s loss.
At first, U.S. Naval Intelligence doubted Commander Enright’s report that he had sunk a Japanese aircraft carrier, since they believed all Japanese carriers had already been identified. After the war, however, his claim was confirmed, and he was awarded the Navy Cross in recognition of his achievement.