Shinano: The Forgotten (And Terrible) First Supercarrier

What is a supercarrier? It’s a simple enough question, right? And so, you would be right to assume it had an equally simple answer, but in fact, no, that couldn’t be further from the truth.

Because rather than the answer to this question being a simple tonnage figure, i.e., “a carrier must displace over ‘x’ tons to be considered ‘super,’” there is in fact no commonly accepted figure, with the exact hurdle to jump changing with basically every person you ask.

It gets more complicated too, because it turns out that no navy on earth even uses the moniker, at least in official classification, and so, it remains the preserve of the commentariat, and the occasional testosterone pumping recruitment piece.

Despite this, at least everyone agrees that whatever a supercarrier is, this, the 60,000-ton USS Forrestal from 1955 was the first one… right? But alas, no, even that is not the case, or at least, it might not be — because may we present you with this, the Japanese carrier Shinano. She rolled out onto the waves in 1944, and give or take, displaced 65,000 tons… which, of course, was more than the Forrestal.

So, what gives? Why have we all forgotten about the Shinano? Why does Forrestal get all of the glory, when another, even bigger carrier existed that was 11 years her junior? Well, worry not folks, because in the next few minutes those questions, and more, shall be answered, as we pull apart the fully nitty of Shinano and her ill-fated service life.

Design and History

As was quite common at the time, Shinano was not a carrier ‘from the keel up,’ but instead was converted from a hull intended for another purpose. And what would make a better donor hull for the biggest carrier ever built up until that point, than that of the biggest class of battleship ever built, not up until that point do note, oh no no, we mean the biggest battleship class ever — the mighty Yamato class.

The Yamatos were simply monstrous things — the absolute pinnacle of contemporary maritime technology. They clocked in at give or take 70,000 tons in displacement, and to give that number some context, the famed USS Texas of WWI, WWII and now museum ship fame, weighs in at a ‘mere’ displacement of roughly 30,000 tons.

The reason for the Yamato’s absurd size was simple, they were to overcome the numerical superiority of the US Navy by being absolute monsters, ones able to deliver a firm shoeing to multiple battleships at the same time and come out the other side alive and kicking. Naturally, to see this done, the Yamatos packed quite the formidable array of arms and armour.

Their teeth came from a dizzying array of nine 460mm guns, the broadest bore guns ever fitted to a warship, which were split into three turrets of three guns. They were also the heaviest ever, with each turret weighing in at 2,730 tons — which, for comparison, was more than an entire Kagerō-class destroyer. As for the rounds these guns fired, they weighed up to 1,460kg, about the weight of a modern hatchback car, and could reach out to a range of 25 miles.

As for armour, the Yamatos had what historian Mark Stille described as “an unparalleled degree of protection in surface combat.” Their belt armour, the bit that sits immediately above and below the waterline, was up to 40.6 cm thick, and their turret thickness peaked at 66cm at its thickest point. To put this into perspective, let us look at the Texas once again, whose belt armour peaks at 30.5cm, and turret armour peaks at 35.6cm — there simply was nothing else afloat that could hold a candle to a Yamato.

The decision to not complete Shinano as the third ship of this indomitable class, after Musashi and the lead ship Yamato, and instead finish her as an aircraft carrier came in July 1942, a month after the disastrous battle of Midway — in which the Imperial Japanese Navy, IJN, had lost four carriers: Akagi, Hiryū, Kaga, and Sōryū. These losses were absolutely catastrophic; carriers were the lynchpin of the IJN’s naval strategy, and without them they found their capabilities severely neutered.

Further to this, elements of the IJN were waning on the idea of battleships anyway and starting to favour aircraft as the preeminent offensive element of a fleet instead — which they evidenced by pointing to the sinking of the British battleship HMS Prince of Wales and battlecruiser HMS Repulse, both of which were sent to the seabed by aircraft in 1941.

These two motivations together made Shinano’s completion as an aircraft carrier a no-brainer.

Naturally, this involved a lot of modifications to her design. The three turrets were omitted altogether, and a 256 metre long and 40 metre wide flight deck that ran the full length of the hull was installed in their place. The superstructure was also radically altered, the large domineering design of a ‘normal’ Yamato class instead being replaced with a much shrunken down ‘island’ style superstructure pushed off to the starboard side on a sponson that overhung the hull ever so. Inside of this was also fitted a command centre for flight operations, that, naturally, ‘normal’ Yamatos didn’t have. The funnel was also fed up through this new superstructure in response to lessons learned from earlier Japanese carriers, which had side hull mounted funnels, and thus could suffer from rather inconvenient visibility issues.

Below all of that, the space normally taken up by the lower sections of turrets and vast magazines for storing 900 car sized shells was given over to hangars and the aviation facilities needed to operate a large aerial complement. But note, we have no idea how big this capacity actually was, partly, this is because we actually know very little about the Shinano, period, for reasons we will get to later on, but also this is because when the decision was made to convert her into a carrier, much of her interior had already been constructed, and since the IJN needed carrier capacity now, the decision was made to leave much of this in place and simply build around it. Therefore, because we know so little about her generally, trying to even just ‘eyeball’ an estimate based on her size becomes difficult, as we simply don’t know what her insides really looked like. Mostly historians, however, when pushed to give an answer, will usually guess in the region of 100 or so aircraft.

While we don’t know much about the exact layout of her hangars, we do know the kind of stuff that was fitted to them. For example, we know that they were fitted with enormous armoured doors to protect the valuable aircraft inside, as well as the whole roof of the hangar being made up of 7.6cm of armoured steel and 2cm of regular steel, enough to fend off the force of a 1,100 lb bomb. Crammed inside of it, somewhere, was also maintenance shops, in addition to ammunition elevators and fuelling stations.

And since we have brought up the matter of Shinano being a bit of a botch job, let’s now discuss her intended role. Despite her imposing size, she was not intended to be a true ‘fleet carrier,’ i.e. one that gets stuck into the chunky action and takes a kicking with the rest of the fleet, instead, she was intended to be a support carrier — one that would hang back and resupply the losses of other carriers from her (potentially) vast hangars.

That was not what the IJN wanted, they wanted her to be the single greatest fleet carrier ever put to sea; a simply terrifying prospect that would turn every Allied sailor’s underpants a healthy shade of brown at the mere prospect of having to face her mighty air arm, but alas, with Japan’s war situation going from bad to worse by the day, naval planners were forced to compromise and plan her for whatever role would quickly get her to sea and doing something for the Japanese war effort — and thus she became a support carrier.

It should also come as no surprise to learn that Shinano’s rushed nature also led to her having quite a few design flaws and defects when she was eventually put to sea, the most dire of which was the incomplete state of her watertight compartments — these being subdivided sections of the hull that can be completely sealed in the event of a hull breach to limit the ingress of water, maintain buoyancy, and thus, ultimately, stop a ship from sinking. They had been pretty much standard on any big ship since the late 19th century, and Shinano, naturally, had them too, just as her half-sisters Yamato and Musashi had before her. But the rush to get Shinano out to sea was so frantic, that many of them had either been found to be inadequately sealed during testing, or simply just not been tested at all — remember that detail, it’ll be important in the next chapter.

Oh, and just to make matters even worse, her bulkheads were also full of holes from unsealed wiring, unfinished ventilation tubes, and yet to be installed water pipes. And that was just the bulkhead issues, because she also had basically none of her water bailing pumps operable.

In addition to just having bulkheads as watertight as a sponge and basically no way of bailing water, however, Shinano’s rushed construction also led to her having a highly compromised centre of gravity and stability. Her hull had been designed specifically with those monstrous turrets and that gigantic superstructure in mind, and without them, her centre of gravity radically changed, which drastically affected her buoyancy and stability. A ship isn’t just like a car, in which you strip out weight and invariably make them better through gains in acceleration, they are very carefully and specifically designed things — and stripping out weight doesn’t necessarily make things automatically better.

Given our specific foreshadowing, and the general discussion of Shinano’s flaws, it will probably come as no surprise for you to learn that she didn’t exactly have a great time of it when she was eventually put to sea, so now, let’s bring this chapter to a close and move on to look at just how badly things went.

Ten Days in Commission, Twenty-Four Hours at Sea

After a little over two years of conversion work Shinano was formally commissioned at Yokosuka Naval Port on the 19th of November 1944, having been given a mere two weeks for fitting out and sea trials beforehand.

The problems began before she had even been commissioned however, as a little over a month earlier, likely on the 8th of October, although we can’t be sure, the unmistakable silhouette of a single American B-29 bomber was spotted overhead — the lonely formation implying very strongly that it was conducting a reconnaissance mission. This meant that the Allies now almost certainly knew not only of Shinano’s existence, but also exactly where she was… and such a big carrier would no doubt be a hell of a tempting prize.

Naturally then, her first order upon her commissioning was to get the hell out of there ASAP, with the IJN General Staff ordering that she depart for Kure by the 28th of November at the latest, where she would hopefully be able to finish being fitted out free from the risk of being randomly reduced to scrap at but a moment’s notice.

Her Captain, one Toshio Abe was furious at this call and asked for that date to be pushed back. To him the risk posed to his unfinished ship by the many Allied submarines which by that point of the war infested the seas of Japan like a pack of ravenous piranhas, was far greater than the threat that the Allies might organise an entire mass air raid just to knock out a single dry docked ship — no matter how tantalising a prize she might be… and Abe was nothing if not prophetic.

His request however, though wise, was denied, and after meeting up with his three escorting destroyers, the Isokaze, Yukikaze, and Hamakaze, he got underway at 6pm on the 28th of November, the very last day that he could get away with, and made for Kure.

Onboard were 2,515 souls, made up of 2,175 officers and sailors, 300 shipyard workers tasked with continuing finishing work as she steamed along, and 40 civilians. Also onboard was her air wing: 50 Yokosuka MXY-7 Ohka kamikaze planes; terrifying contraptions which consisted of a rocket motor, a 1,180kg bomb, a cockpit, some wings, and not much else — she had been tasked with delivering these to the Philippines and Okinawa after her fitting out had been completed.

As she was still undergoing fitting work while at sea, most of her watertight doors and hatches were left open in order to afford the workers easier access and speed up their work, and even more worryingly still, many of the manholes in her several layered hulls were left open for the same reason.

It should have only taken 16 hours for Shinano to cover the 300 miles to Kure, but as we have hinted at rather strongly, she would never make it.

The submarine USS Archerfish first detected Shinano at exactly 8:48pm, but for now, all remained well, and Abe remained confident as Shinano had detected the submarine over an hour and a half prior, and so was on high alert for her making an appearance. Things continued to get better too, at least for now, because when detecting Shinano, Archerfish had had to reveal herself, and so Shinano’s destroyer escort broke away and scared off the would-be attacker.

Abe then found himself at a tactical crossroads, did he A), keep his ship dead straight, dump the engine order telegraph, and gun it, knowing full well that he could outrun a submerged submarine, or did he B), move in a defensive zig-zag pattern, lest his eagerness to get away inadvertently make him easy pickings for any other Allied submarines in the area? He chose option B).

As a result of this choice, it was only a matter of time until Archerfish caught up, which she did no later than quarter to ten pm — when Shinano’s lookouts spotted the submarine returning to the surface in order to recharge the batteries it used for underwater running. History could have been changed right then and there, the Archerfish had been caught with its pants down and was a sitting duck, but alas, no.

Despite the most tempting opportunity before him, Abe ordered his escort to not engage and maintain their formation; fearing that the almost too good opportunity before him was a trap intended to lure away one of his escorts, and leave a nice big opening into which another, yet to be detected Allied submarine could duly send some torpedoes.

The Isokaze was having none of it however and broke off to destroy the Archerfish — which would have been but a trifle of a task while it sat vulnerable on the surface. But no, it wasn’t meant to be — because after some… ‘heated’ discussions over the radio, in which Abe told the destroyer of the importance of respecting rank and obeying orders, it returned to formation.

He did change his approach however, as he ordered his motley flotilla to put the submarine behind them, aim dead ahead, and punch it — finally having twigged that the submarine he could actually see was a far more pressing concern than any potential other danger.

This worked great, for a while anyway, as at 11:22pm Shinano’s rushed construction came back to bite Abe on the rear — a bearing had overheated, and he was forced to reduce his speed to 18 knots, give or take exactly the same speed of Archerfish, lest he lose use of a propeller outright. He also couldn’t keep going straight forever, sooner or later he would have to turn to make course to Kure, and when he did, it would only be a matter of time until Archerfish was back on top of him, at the perfect side-on angle for an attack.

That time came at 02:56am when Abe turned Shinano southwest. A mere eight minutes after that, at 03:04am, Archerfish had more or less closed the gap and submerged to begin making its attack run. Her captain, Commander Joseph Enright ordered a full volley of torpedoes prepared, and then, he slowly closed the gap ever more, and waited for the perfect moment to strike, which happened a few minutes later, when Shinano turned due south, and pointed her entire exposed side straight at Archerfish.

Enright gave the order to fire at 03:15am and sent six torpedoes right at the perfect target before him. He then immediately dived to 400 feet — because between the reload time of his torpedoes, and the inevitable depth charge reprisal from Shinano’s escort, he knew he wasn’t getting another chance to take that shot.

Four of those torpedoes found their target. The first struck towards Shinano’s stern, destroying and subsequently flooding an empty aircraft fuel storage tank and killing many of the engineers who were sleeping in their quarters above it. The second also struck the stern, right at the very back in fact, on an engine room — immediately costing Shinano the use of a propeller and half of her engines as water poured in. The third torpedo hit further up the ship, striking dead on a boiler room, immediately putting it out of action, flooding it, and killing every man on duty there. The final one hit an anti-aircraft gun magazine, causing an enormous explosion that took out an adjacent compressor room, damage control station, and oil tank.

Had Shinano been built properly, this wouldn’t have been her end. Make no mistake, it certainly wouldn’t have been ideal, and getting home no doubt would have been quite the arduous task, but things, touch wood, would have been fine in the end. But Shinano wasn’t built properly, and so the freezing water of the Pacific Ocean just kept pouring in, and in, and in, through all of the many holes in her internal bulkheads.

And of the precious few efforts that could be made to save Shinano, or at least delay her sinking, all but none of them were actuated. Her officers, Abe included, were convinced that the four torpedo impacts represented no ultimate danger to them, they were in a carrier-ised Yamato after all. This led to Shinano maintaining full speed ahead, which only served to ram yet more water into her ever filling up hull.

It took only minutes for her to begin listing at 10 degrees to starboard, and this soon increased to 15 degrees come 03:30am. At this point Abe began to grasp the true reality of the situation and began ordering for frantic efforts to save the ship, but nothing tried worked — from having Hamakaze and Isokaze tow her, to counterflooding compartments, it all came to nought.

Shinano ultimately slipped beneath the waves at 10:57am, taking 1,435 souls with her, Abe included. In that moment, she also became the largest ship ever sunk by submarine, even to this very day.

The goliath of a ship, very possibly history’s first ever supercarrier, had barely survived 10 days in commission, and not even 24 hours at sea.

Historiography and Conclusion

So ends the tale of Shinano.

As for the matter of whether or not she was a supercarrier… we’ll leave you to make up your own mind on that — it’s such a subjective question that there’s little point us trying to authoritatively answer it today.

What we will do however is take the time to clear up a few things about her that didn’t really fit into the main body of the piece; remember when we said that we know surprisingly little about her? That wasn’t us overhyping the situation to be dramatic, it really is shocking how little we know.

This gap in our knowledge is the result of the fact that Shinano was constructed in near total secrecy, was barely in commission for 10 days, and the fact that as the war was looming towards its end, the IJN burnt basically every bit of paper about her.

So scant is information on Shinano in fact, that there are three known photos of her. Literally, just three. There is one from the aerial reconnaissance flight we mentioned earlier, one of her on the bottom of the sea today, and one that was taken by pure fluke as she sailed to Kure by a random Japanese civilian who just so happened to have his camera on him.

It’s a weird thing to say when discussing something so modern, but we really do know bugger all about her in the grand scheme of things.

With that in mind, let us also explain where we got the bulk of our information from today, because the lack of information out there about Shinano can lead to secondary sources… ‘varying,’ shall we say, and so it is worth being transparent just in case what we have said today doesn’t line up with your own reading. The primary source used was The Imperial Japanese Navy by Anthony Watts and Brian Gordon — of all the books considered, this one was the most open about what we didn’t know, and thus we deemed it likely the most reliable.

Key Takeaways

• The term ‘supercarrier’ lacks a universally accepted definition, with no agreed-upon tonnage figure.
• The USS Forrestal is often cited as the first supercarrier, but the Japanese Shinano, launched in 1944, was larger.
• Shinano was converted from an unfinished Yamato-class battleship hull, originally designed to be the largest and most powerful battleship ever built.
• Shinano’s rushed conversion and subsequent sea trials led to significant design flaws, including incomplete watertight compartments and compromised stability.
• Despite its size and potential, Shinano sank after being torpedoed by the USS Archerfish, taking 1,435 souls with it, just 24 hours into its maiden voyage.

Sources

• Original MegaProjects video: Shinano: The Forgotten (And Terrible) First Supercarrier
• Hero image source by Quintin Soloviev / openverse, by.

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