A question concerning IJN CLs

[Shawn]

The Japanese light cruisers, Oi and Kitakami were converted to Long Lance carriers during 1941. Subsequently in the later part of 1942 they were converted again to fast transports. The question is why? These two CLs would have been a terror in the confined waters around Guadalcanal. Does anyone know if their performance as torpedo cruisers was somehow lacking?

[CaptHawkeye]

A big problem that the IJN was having was that pretty much all of their cruisers and destroyers weren't getting anywhere near the number of torpedo hits they wanted.

http://www.navweaps.com/index_tech/tech-067.htm

The Japanese indirectly established a minimum hit rate of 15% for their torpedoes if they wanted to really hurt the US navy. Ultimately they couldn't get above 7%, barely half that minimum. As the war went on the Japanese put less and less emphasis on having their Destroyers and Cruisers try to perform front line actions on their own after they were severely attritioned during the Solomons Campaign. More emphasis was placed on anti-aircraft protection but that was difficult to achieve due to how much space on their ships was already devoted to other weapon systems. Late war DDs like the Akizuki Class ditched the usual Torpedo-Heavy act and concentrated more on AA which was desperately needed.

As for converting Oi and Kitakami to transports, after Guadalcanal the Japanese were desperate to evacuate their remaining military forces off of the island. Fighting the USN became secondary to evacuating personnel. Besides, two or even ten more cruisers weren't about to make Japan's situation any better in the area.

[Zinegata]

Not to mention the Long Lance mounts can end up exploding rather catastrophically if the mount gets hit by even low-calibre shells. While this wasn't much of a problem in Guadalcanal with the US fire control (especially at night) being subpar, it proved to be fatal to at least one Japanese cruiser that fought against a destroyer escort at the Battle off Samar. I've even heard (but couldn't confirm) that a CVE even managed to cripple a second Japanese cruiser by scoring a Long Lance mount hit - using its sole 5-inch cannon!

[Shawn]

As the war went on the Japanese put less and less emphasis on having their Destroyers and Cruisers try to perform front line actions on their own after they were severely attritioned during the Solomons Campaign. More emphasis was placed on anti-aircraft protection but that was difficult to achieve due to how much space on their ships was already devoted to other weapon systems. Late war DDs like the Akizuki Class ditched the usual Torpedo-Heavy act and concentrated more on AA which was desperately needed.

As for converting Oi and Kitakami to transports, after Guadalcanal the Japanese were desperate to evacuate their remaining military forces off of the island. Fighting the USN became secondary to evacuating personnel. Besides, two or even ten more cruisers weren't about to make Japan's situation any better in the area.

All very true. However, these two ships were taken in hand to be modified into fast transports in August of '42. There is no way the IJN could foresee the need for transports at that time. They were still looking for the mythical decisive battle which, I think, these two ships would be perfect for.

[Sea Skimmer]

Actually the decision to convert them was taken immediately after the US landing on Guadalcanal. By this point Japan very much realized the battleship was eclipsed, but still very useful as later events would show. The threat of air attacks made a floating bomb like the torpedo cruisers a real joke. Japan knew that risk too, which is why its heavy cruisers had armor above the torpedo tubes. Anyway Japanese defensive strategy had always called for mobile counter attacks to a US thrust into its new possessions. The decisive battle was supposed to be the end result of those actions, but not the only thing that would happen. Japan had already converted a number of old destroyers into fast transports before the war, the light cruisers were just an expansion on that useful policy.

As for the torpedo tubes themselves, the transport conversions actually retained the forward six quadruple mounts though in some cases the tubes would be loaded with supplies. Four mounts were removed to make space for two 14-meter landing barges. Depth charges, and a few 25mm anti aircraft guns were also fitted to each ship. The conversion was carried out very rapidly, and both ships left Kure on September 9th to embark Special Naval Landing Force troops, who were then immediately taking to the Shortland Islands. The cruisers then made a series of shuttle runs between various forward bases and later operated further west. Plans for a full transport conversion with no torpedo tubes and fitting a new main battery of 127mm anti aircraft guns were never carried out because they would have taken too long.

Oi was sunk west of Manila by US Submarine Flasher 19 July 1944. Kitakami was converted into a Kaiten carrier during late 1944 but then effectively immobilized by lack of fuel. US air raids caused minor damage and she survived the war. She was broken up and scrapped in late 1946-47. A third conversion was planned but never carried out, IIRC the ship was converted directly to a transport instead. Before and throughout the war Japanese warships of all types, including both Yamato class battleships and a number of aircraft carriers were used as transports. Japan was a poor nation and could not nearly afford enough shipping to meet the demands of its far flung empire of conquest.

[Zinegata]

Japan knew that risk too, which is why its heavy cruisers had armor above the torpedo tubes.

Not enough to save the Chokai from 5 inch shells though .

[Stuart]

It's also worth noting that the Japanese were short of torpedoes; manufacturing rates didn't compensate for use and delivering the torpedoes to the front line was a real problem. ***This is a guess but*** I suspect if we look deep enough we'll find that there simply were not enough torpedoes available to give the torpedo cruisers their full outfits. Therefore since the tubes were empty and transports were needed, remove said tubes.

[Shawn]

It's also worth noting that the Japanese were short of torpedoes; manufacturing rates didn't compensate for use and delivering the torpedoes to the front line was a real problem. ***This is a guess but*** I suspect if we look deep enough we'll find that there simply were not enough torpedoes available to give the torpedo cruisers their full outfits. Therefore since the tubes were empty and transports were needed, remove said tubes.

Interesting...I never thought of it as a production problem. Considering the overall state of the Japanese economy, it does make sense though.

[Zinegata]

I dunno. I haven't heard of ammunition shortages being a big problem for the IJN. There weren't really that many big fights (especially for the surface fleets) to expend gun ammunition and torps.

[CaptHawkeye]

Not true. Just look at The Battle of the Sunda Straight. Even for relatively tiny battles the Japanese would expend ridiculous amounts of ordinance on targets because the general philosophy for the IJN was that their opponent's naval assets had to be annihilated as quickly as possible. After all the IJN was a tiny force fighting enemies much bigger than it.

Besides that, merchant tonnage usually could not be diverted in enough strength to keep frontline bases in supply. What merchant ships the IJN had also had to be closely escorted and only at night otherwise they'd get scuppered. For gun and AA ammunition it's not as hard. Torpedoes though, especially the Long Lance, are very big, expensive weapons that are difficult to keep in constant supply.

[Sea Skimmer]

References do exist to shortages of Japanese aerial torpedoes. The torpedo planes which sank Prince of Wales and Repulse for example had only one torpedo apiece in all of Indochina. In another case during the Indian Ocean Raid it was considered reported to have been considered fortunate that a torpedo strike was not flown off to attack British heavy cruisers, as bombing sank them first, and since torpedo planes could not land with torpedoes onboard the weapons which were in short supply would have been lost. That is mentioned in Shattered Sword.

It really shouldn’t be a surprise. Torpedoes are also simply the most expensive type of ammunition around in WW2, other then the atomic bombs, and even today only large ballistic missiles are more expensive then modern heavyweight torpedoes. A Tomahawk cruise missile is cheep compared to a Mk48 torpedo.

Japan was fighting like crazy in China, and funding for munitions would have heavily favored small caliber shells and smaller aerial bombs to fight that war. Heavy bombs and torpedoes and big naval shells would all be limited production items. Indeed Japan had to convert existing 16in shells into bombs for the Pearl Harbor Attack because no bombs heavier then 250kg existed in the IJN inventory. Japan was a poor nation, and even in wealthy nation’s high end weapons like warships, tanks and aircraft are always easier to funded then mundane stuff like ammunition, logistics transport and communications gear. Japan being a military dictatorship didn’t change that reality, all the more so since the Army and not the Navy was on top of the power structure.

The Long Lance couldn't have helped but be absurdly expensive. The thing is powered by a 520hp steam piston engine that had to fit inside a 24in tube and run reliably while having cold seawater sprayed inside it... not easily done even today. Japan was very weak in light and medium industries and skilled workers to support that kind of production. I'm sure they could have expanded torpedo production nicely for the cost of a Yamato turret. Also the Long Lance was fairly new, only introduced in 1935 so Japan did not have a long time to stockpile them in peacetime prior to the China War, unlike its 21in and non O2 powered 24in types.

So a torpedo shortage is very plausible, particularly after actions like the Java Sea in which over 140 torpedoes were fired. But I think the transport requirement is overwhelmingly compelling on its own as reason for the conversion. The lack of gun power for the torpedo cruiser to defend itself from screening units and utter lack of AA capability are also good reasons for the IJN to have wanted to rid itself of such freakish units.

[Sea Skimmer]

Not enough to save the Chokai from 5 inch shells though .

Well what do you want, 5in would have been pretty flat trajectory at the ranges involved, and its only 25mm of roof armor anyway, though since almost no one survived the battle from Chokai the cause of her explosion is still not known for certain. She was hit by a 500lb bomb around the same time. The point just being they thought about it, and at least strafing shouldn't have exploded them.

In the same battle meanwhile Suzuya was disabled by one near miss bomb, then a second near miss exploded her torpedoes as well, causing uncontrolled fires that forced her scuttling. Japan designed the heavy cruiser torpedo mounts so that when run out from under the armor the warheads were held out past the edge of the hull, but it doesn't seem to have done them any good. IIRC seven Japanese cruisers had torpedoes explode during the course of being lost, but once more IIRC (I compiled this out of Japanese Heavy Cruisers in the Pacific War once) at least two had torpedoes explode but survived.

[CaptHawkeye]

It also doesn't help that the Long Lance was a particularly sensitive torpedo due to its power plant. Their were a lot of cases of them just fucking exploding in the factory because the system was so dangerous. Of course Japan's industrial methods probably ignored factory safety in favor of raw output.

Torpedoes are also simply the most expensive type of ammunition around in WW2, other then the atomic bombs, and even today only large ballistic missiles are more expensive then modern heavyweight torpedoes.

Not surprising when you realize a torpedo is a basically a big aquatic robot with a warhead attached to it.

[Sea Skimmer]

It also doesn't help that the Long Lance was a particularly sensitive torpedo due to its power plant. Their were a lot of cases of them just fucking exploding in the factory because the system was so dangerous. Of course Japan's industrial methods probably ignored factory safety in favor of raw output.

Well pure oxygen is dangerous, no matter what you use it for. Japan had pretty bad ammo safety and few weapons safeties in general, but I suspect they in fact had to take great care in ordered to be able to build oxygen powered torpedoes at all. The Type 93 has been described as requiring measures like cleaning every piece of piping with alcohol before assembly, and then flushing the system out again afterwards, as well as during operational service. The slightest line contamination would become reactive with the O2, causing a pressure spike, rupture and thus explosion. Cleaning and careful sealing measures would have eaten up a huge number of hours at phase of production besides the generally high need for quality control in a torpedo.

Japan really suffered too from the fact that it had almost no one in the civilian world who know how to work on automotive systems. People had not even seen cars in many instances. An aircraft or torpedo isn't the same as a car, but the propulsion and controls works on the same principals. Instead Japan was stuck having the military or factories teach every last basic deal about what a piston even is to a worker upon arrival. The Japanese school system was largely useless since it was constitutionally mandated to place lessons on loyalty to the Emperor above actual education. Brilliant idea if only they had exploited it fully and introduced the kamikaze in 1942.

[Shawn]

Data from Warship 1991, "Japanese Oxygen Torpedoes and Fire Control Systems" by Dr. Jiro Hitani, Hans Lengerer and Tomoko Rhem-Takara.
Type 93 model 1 mod 1 & mod 2 ....1150 produced from 1936
Type 93 model 3................................560 produced from 1944

Information taken from a thread on Navweaps.com

[Stuart]

Data from Warship 1991, "Japanese Oxygen Torpedoes and Fire Control Systems" by Dr. Jiro Hitani, Hans Lengerer and Tomoko Rhem-Takara.
Type 93 model 1 mod 1 & mod 2 ....1150 produced from 1936
Type 93 model 3................................560 produced from 1944

Information taken from a thread on Navweaps.com

There's your answer then. Barely enough torpedoes in the first group to equip Japanese ships with their initial load-out and barely enough in the second to replace those fired. There simply aren't enough torpedoes to go around and that excludes problems with transport and handling.

[Pelranius]

Every time I read about Japanese design idiosyncrasies (to put it generously) and their logistical and industrial deficiencies, it makes me wonder exactly what the Japaneses high command and privy council were thinking by going to war, and how the 1940 leadership was even remotely connected with the folks who lucked out in 1904-5.

[CaptHawkeye]

The leadership of the 1930s pretty much had no connection at all with 1904-05 Japan. The Depression gave the military an excuse to basically launch a quiet Coup of the government in the early 1930s and replace it with an authoritarian state which was totally submissive to the Emperor. ("Quiet" is a relative term though. Their were no less than 4 in a row assassinations of the occupying Prime Ministers. Their were also numerous cases of threats made to Diet members and critics of the military. Threats which frequently ended up being carried out.)

The Emperor himself was very susceptible to "advice" from the military who were often able to convince him to perform the most mindlessly aggressive acts. In other cases they didn't need to convince him of anything, because no matter what the apologists say Hirohito was pretty violently militarist himself.

Of course, even in 1905 Japan was particularly ethno-centric and very convinced of its racial superiority to its Asian neighbors.

[Sea Skimmer]

Prior to the 1920s and 1930s military takeover Japanese national military policy was actually based around what they called ‘total war preparedness’, basically turning the country into a garrison state. This was being done in large part because Japans leaders at the same time saw how weak Japan was, and thought extensive preparations, military and civilian, would be the only way to wage even a defensive war. The Japanese at this time even foresaw how absurdly vulnerable they would be to strategic bombing, which fed into why they later decided to ATTACK.

The new Japanese military government meanwhile believed its own nonsense on the samurai spirit, because that's what they had been raised on, and saw all that preparation as the perfect opening to attack when spirit would be mightier then the bullet. Of course, since Japan had already spent more then ten years mobilizing, and four years being sucked deeper into China by 1941 they were already at the limit of what they could do. Japanese military leaders, particularly the Army were just far too stupid and blind to understand that until Saipan fell. By then the only option left was the KAMKAZI, and a somewhat effective switch to defensive tactics not based on banazi charges. In order words, tactics that accepted inevitable defeat in favor of attrition. The original Japanese thinking was fine, if it was the year 1200AD or so. As we see in the Japanese invasion of Korea-China in the late 16th century, they have a long history of incredibly stupid military moves. They only knew how to fight each other, which is why Japan then went back into isolation after that flop.

[CaptHawkeye]

Japan's entire history of military propaganda literally ended in one huge backfire. Japan itself ended up believing its own horse shit pre-conceptions of race and the Emperor's supernatural intervention more than their enemies did. Beliefs which did everything to hasten the defeat of the Empire. I mean, you had guys as late Iwo Jima who were willing to kill themselves the moment they failed to hold a single foot of land. Did it occur to them that they were far more useful to the defensive effort alive rather than dead? Nope. It was all about some bullshit buzzwords like Bushido.