IJN Shinano, Japan's Largest Aircraft Carrier
The IJN Shinano, named in honor of the Shinano province, was originally laid down as a Yamato class battleship. However, battle losses during the course of the Second World War led to Shinano's conversion to an aircraft carrier during construction. She was the largest WWII aircraft carrier.
IJN Shinano: Originally the Third Yamato
In the early 1940's after abandoning a series of naval arms limitation treaties Japan was building a series of the most powerful battleships ever seen. They were called the Yamato class, and at more than 800 feet in length and 60,000 tons they were behemoths. The two that were eventually completed - Yamato and Musashi - went on to be two of the most legendary warships in Japanese history.
But the Battle of Midway in 1942 proved that aircraft carriers were the dominant naval vessel in the Pacific. Japan lost four of its largest at Midway, and immediately began a crash program to build or convert as many ships that could be deployed as aircraft carriers as possible. Its hull only recently completed, IJN Shinano was a prime candidate for conversion.
With plenty of space to work with, the Shinano promised to be a potent aviation platform. From the outset her modified design was intended to outclass any other carrier afloat and leave her able to survive battle damage that sank many of her predecessors. Notable among her design features was the inclusion of an armored flight deck capable of withstanding the explosive force of any bomb dropped by any aircraft that could be launched from a contemporary aircraft carrier.
With over eight hundred feet and seventy feet of length and one hundred and thirty feet of width (measured at the flight deck) to work with, Shinano was capable of fielding the largest airwing of any carrier constructed by the end of the Second World War. Nearly 140 aircraft could fit in her capacious hangar, and by establishing a deck park this could likely be increased.
IJN Shinano was redesigned with the lessons of the Battle of the Coral Sea and the Battle of Midway in mind. Aside from the thickly armored flight deck, she was extremely well protected by sixteen 5" heavy anti-aircraft guns as well as over one hundred and forty 25mm autocannons. These would provide a potent screen of flak over and around the Shinano capable of shredding enemy aircraft so bold as to attack her.
As far as her machinery went, Shinano was a relatively slow aircraft carrier with a top speed of around twenty-seven knots. However she could sail almost 10,000 nautical miles without refueling while moving at this speed, which given her air wing size meant that she could pose a threat to US bases in most if not all the western and central Pacific.
IJN Shinano Deployment Possibilities
By her launch in late 1944 Shinano was one of the last aircraft carriers afloat in the Japanese Navy, and Japan herself was facing a daunting array of foes closing in on all sides. A serious lack of fuel oil coupled with the loss of most of its forward bases in the Pacific to the US advance meant that most Japanese warships operated fairly close to their bases at this point in the war.
Because ground based aircraft (Japanese aircraft tended to have very long ranges) could provide air cover for the fleet in these dark months, Shinano became more valuable as a support carrier for the naval strike forces than a major fleet carrier. Her combat airwing would be relegated to a third of her capacity, but her hangar would then be filled with vital reinforcement aircraft including "Ohka" manned suicide rockets. Her decent speed coupled with a major load of these weapons meant that she could rapidly reinforce a beleaguered garrison and still help to cause serious casualties among the Allied land, naval, and air forces.
Her existence was apparently unknown to US naval planners, and so it was fortuitous that her maiden voyage was spotted by a US submarine that happened to be in the right place at the right time.
In late 1944, when the course of the war had taken a definitive turn for the worse for Japan, Shinano was ordered to be moved from Yokosuka near Yokohama south to Kure to complete her fitting out process - a vital prerequisite to being sent into open battle. She was escorted by a screen of three destroyers, and while this may seem like a weak force, she was meant to remain close to land and under friendly air cover during the course of her voyage. US submarines were a threat, but warships travel faster than merchant vessels, and only a very lucky submarine could hope to catch a carrier and not be destroyed by her escorts. The USS Archer-Fish got lucky. She put four torpedoes into the IJN Shinano, which capsized and sank with heavy loss of life due to crew inexperience with damage control and the fact that she was not intended to be combat ready for some time.
Shinano - Moved for Fitting Out without Rudimentary Watertight Doors
As Japan's position became increasingly desperate, her leaders began to make decisions that were in hindsight incredibly risky. The treatment of the Shinano is a case in point. In November 1944 she was ordered, to the dismay of her captain, to move from Yokosuka to Kure to help shore up the southern defenses and prepare to be fully fitted out prior to commissioning and sailing to war. Although her captain plead for more time to finish installing rudimentary safety features in a warship such as watertight doors and effective pumping mechanisms he was ignored.
Naval vessels are complex meldings of steel and iron that rely on maintaining watertight integrity in order to remain afloat. If you take a hunk of metal and toss it into the sea, it sinks rather quickly. Only when that metal is shaped so that significant quantities of lighter than water substances like air and ballast are trapped within the metal structure will the metal be sufficiently buoyant to float. Naval vessels use pumps to eliminate seawater that enters the vessel, and a series of segmented compartments separated by watertight doors that can isolate portions of the ship that are being flooded so that the damage to the vessel is contained.
IJN Shinano was not yet equipped with watertight doors and her pumping systems were not fully operational when she was ordered to sail for Kure. In addition, her crew was a combination of inexperienced sailors and dockworkers ill trained to handle a major emergency.
USS Archer-Fish Sinks the IJN Shinano
Not only was the Shinano dangerously incomplete in regards to ability to sustain and recover from battle damage, she had the misfortune to come across a US submarine, the Archer-Fish, only hours after departing Yokosuka. The submarine picked her task group up on radar and approached - probably believing Shinano to be a large merchant ship or group of smaller merchant ships considering her escort and the fact that her existence was unknown to US Naval authorities.
After a four hour cat and mouse approach - made easier by the fact that not all of IJN Shinano's boilers were online and her top speed was reduced - Archer-Fish fired six torpedoes at the aircraft carrier and dove deep. Of the six, four struck the carrier and immediately caused serious flooding along her starboard side.
Ironically, the damage was not immediately lethal. Shinano's crew bravely fought the flooding brought on by the four torpedo hits for four hours before she was no longer able to sustain forward progress, and even then the ship remained afloat for more than two additional hours. Her crew tried to pump out the seawater, they even tried to counterflood to correct a rapidly developing list to starboard that threatened to capsize her.
But in vain. Shinano's pumps didn't work correctly, her lack of watertight compartmentation hindered efforts to counter flooding, and her crew - albeit brave - did not have sufficient experience in damage control procedures. Finally, she capsized and sank taking almost 1500 men with her - including her captain. The IJN Shinano remains a little over 100 miles off the Japanese coast.
Shinano Sources and Image Credits
Janes Fighting Ships of World War II, 1946 Janes Publishing Company, 1994 reprint edition
Churchill, The Second World War, 1959 Time Life
Images all via Wiki Commons courtesy (respectively) of Takeo Kanda, the US Government, Hiroshi Arakawa, and the US Navy
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