Originally laid down as a Yamato-class battleship, the Shinano was only partially completed as an aircraft carrier by the time of her sinking in November of 1944.
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The IJN Shinano served the Imperial Japanese Navy (IJN) as a large fleet carrier during World War 2. She originally existed as a hull meant for the Yamato-class series of battleships of which the IJN Yamato became its most famous performer during the war. The class represented the Yamato itself and her sister ship, the IJN Musashi. Yamato ended her career on April 7th, 1945 in a suicide action related to the fighting on Okinawa while Musashi was lost to the enemy during the Battle of Leyte Gulf on October 24th, 1944. Shinano saw her keel laid down on May 4th, 1940 by Yokosuka Naval Arsenal though in 1942 it was decided to convert her still incomplete hulk to that of an aircraft carrier to help shore up losses elsewhere - she would become largest carrier ever built and sunk in the war. Her name stemmed from the Shinano Province of Central Japan and she was launched to sea on October 8th, 1944 and was sunk by an American submarine crew that November.
The Shinano held origins was born in the 1939 initiative put forth by the Japanese Navy as the "4th Naval Armaments Supplement Program" - a program looking to continue expansion of Japanese firepower in the Pacific. As such, the Shinano was laid down with the intent that she serve as a Yamato-class battleship though the Japanese Navy setbacks, beginning with the Battle of Midway where four aircraft carriers were lost, forced authorities to reconsider the vessel as a make-shift fleet carrier. Once converted, she held little of her Yamato identification for she lost much armor protection and lacked the formidable turreted main guns of her sister ships. Instead, the vessel followed conventional wisdom regarding carriers and received a flat-top, inline flight deck with an offset starboard side island superstructure (with attached smoke funnel). The type was cleared to carry up to 47 naval attack, reconnaissance and fighter aircraft to counter the valuable American carrier group strength. As completed, the vessel weighed 65,800 tons under standard load and upwards of 69,000 tons under normal military loads. Her running length was 872 feet with a beam of 119 feet and draught measuring 33 feet, 10 inches. Power was served through 12 x Kampon water-tube boilers developing power to 4 x geared steam turbines driving 4 x shafts through 150,000 shaft horsepower - the same as in all the Yamato-class ships. This provided the vessel a maximum surface speed of 27 knots in ideal conditions, making her quite a fast carrier design. Her range was listed at 10,000 nautical miles (equal to about 12,000 miles) when proceeding at 18 knots. She provided quarter to some 2,400 officers, sailors, specialist and airmen. Defense was rather strong through 8 x 127mm Type 89 Dual-Purpose (DP) twin-barreled cannons supplemented by 35 x 25mm Type 96 anti-aircraft cannons in triple mounts. There were also 12 x 120mm (4.7in) anti-aircraft rocket launchers available with a 28-round supply. During her construction (as well as during the building of the Yamato and the Musashi), the vessel was erected in secret to avoid prying eyes and maintain an ultimate element of strategic surprise.
Despite all of the work, the end of the road for Shinano came quickly in November of 1944. She entered transit from her construction berthing at the Yokosuka Naval Shipyard en route the Kure Naval Base to begin accepting a stock of aircraft and armament fitment. However, she came under the watch of the USS Archer-Fish (SS-311) of the United States Navy during the voyage. Archer-Fish was a Balao-class attack submarine commissioned in September of 1943 and went on to lead an excellent service life for the Americans, surviving the war and ultimately given up as a target hulk off the coast of California in 1968. The American boat engaged the weakened Shinano and landed four torpedoes into her despite a Japanese destroyer presence. In short time, the Shinano listed to starboard - usually the death knell for any warship - and this was followed by a complete power loss which left the vessel a floating target. An attempt was made by accompanying ships to save her from sinking but the order was eventually given by her captain to abandon ship. The Shinano then found the bottom of the ocean on November 29th, 1944 after sinking at the stern. The loss delivered yet another critical blow to Japanese naval aspirations at this late stage in the war. 1,435 Japanese service personnel and civilian workers perished in the assault while some 1,080 souls were ultimately saved.
It was expected that the Shinano would have undertaken formal sea trials into late-1944 and early-1945 before being commissioned sometime in the late spring. However, mounting losses to Japanese naval assets pushed construction of the Shinano along as the Allied noose around the Japanese mainland was ever-tightening - the harried pace leaving quality control in a rather dubious state. Her design also proved flawed on the whole, for her quick-paced flooding ultimately doomed the ship and her crew in short order.