You’re probably familiar with the massive 380mm rocket propelled shell used by the
German Sturmtiger. With both this unique armament and the unique vehicle which
carried it there is really no surprise that many are captivated by the machine. However,
what if I told you that far to the East their Japanese allies were utilizing a projectile
which would make the Sturmtigers look like a dollar store firecracker? Today we take
what could be one of the first in depth looks at the Japanese 447mm spin stabilized rocket.
Knives and other bladed weapons have an incredibly long history in warfare stretching back thousands
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Although this is not quite the normal subject for a Cursed by Design video as it does not
directly relate to a tank I think this weapon thoroughly fits the name. Before we get into
the massive rocket itself I think it makes sense to briefly cover some of the Japanese
rockets which led up to it. Bear in mind most of this info is coming from Allied reports from
during and after the war so some information may not fully represent the actual projects.
Japan was a fairly late adopter of rocket technology and due to this they were far
behind other powers at the time in regards to their fielded weaponry. However, thanks to
their alliance with Germany they did secure some assistance from them which can be seen in later
examples of their rocket-propulsion development. The earliest examples of Japanese rocket-propelled
projectiles were quite crude improvised attempts at the concept with the Type 10 and Type 3 being
quite literally a rocket strapped to a 60 kilogram aircraft bomb. Similarly the 30cm rocket was a
modification to a 250 kilogram bomb allowing it to be to launched from a similar launcher.
Interestingly this was also something done on the other side by the Americans with a similar
rocket propelled bomb. We can see it pictured here with the launcher being towed by a Jeep.
Following these improvised weapons we finally begin to see the German influence with the Naval
20cm spin stabilized rocket. As the name suggests this rocket is designed to spin as it flies to
stabilize the projectile like the rifling in a gun barrel. The projectile for this was a modified
Naval shell with the rocket attached to it. This would be followed by the first production rocket
known as the Army 20cm, and the Type 4 launcher. Unlike the previous versions it was now a tube
style launcher instead of just a crude trough shaped one. At some point the Navy 20cm also
seems to have received an upgraded launcher but when is unclear. These do seem to have been used
in combat with launchers and projectiles being captured by Allied forces in areas like Luzon.
These previous models can be seen as both Japan's introduction to the technology
followed by a reasonably good production version. However you didn't click on this
video for the sensible designs. This brings us finally to the massive 447mm projectile.
By now you may be wondering how exactly the spin stabilization with the rocket works and I think
it is worth exploring as it is a key part of how this rocket functions. For this let's
first look at the Sturmtiger for comparison. The payload of the projectile is located on
the top with a fuze on the very end. On a normal artillery shell the section behind that would be
the propellant charge but as this is a rocket propelled projectile it instead contains the
rockets. On the butt of the projectile is a smaller component which contains nozzles
to create what is referred to as the Venturi effect. That effect is something you need to
watch a dedicated video to truly understand but to super oversimplify it they work to increase
the velocity of the rocket exhaust. Unlike the Japanese design, though, the Sturmtiger relied
on small nubs located at the base of the shell, as you can see here, to generate a stabilizing spin.
As for the 45cm Japanese rocket the overall layout was essentially the same with the payload and
rocket assembly being only slightly different in shape. The real change is the way the nozzles are
positioned. These are set up in what is referred to as a “convergent-divergent venturi’ and looked
like this. Essentially this would generate a spin by using various angles for the different nozzles
causing the exhausts to create a spinning motion which would then cause the entire projectile to
begin to rotate in flight. This same system was used on a number of German designs as well once
again showing their influence in the Japanese development. Hopefully I didn’t lose any of you
there by boring you with the details but I figured at least a few of you might find that interesting.
Weighing in at about 1500 pounds or 682 kilograms this enormous shell was capable of carrying a
payload of 180 kilograms of type 98 explosive. From some quick asking around, Type 98 explosive
is probably about the same as TNT so the rocket would likely perform similarly to other ordnance
with that amount of TNT filler. Similar in design to its smaller cousins the 447mm,
often referred to as 45cm by Allied reports, could deliver this payload at a speed of 460
feet per second according to a test at Aberdeen. All of this would be for nothing if the projectile
did not have some form of launcher. We can pretty confidently assume that this project was still
very much in its infancy as the reports indicate most, if not all, of the launchers found for this
weapon were crude or improvised. The one shown in this photo was created by Ordnance Team no.3
to test the rocket. I have been unable to locate an actual photograph of the Japanese launcher,
but within the file Ed from Armoured Archives provided me there is an illustration of what is
said to be the complete launcher. In the British files this design is described as quote “similar
to an ox-cart” . American intelligence also reported a similar design saying it was built
from a 12 foot launching platform held on 4 foot wooden wheels. This launcher also seems
to have a firing mechanism and wheel brakes as shown in the British drawing. The exact setup
of this launcher for use is unclear to me as the Allied documents claim the launching of the
rocket is so powerful that it would completely destroy the launcher. For this reason it seems
odd that the Japanese would bother to include wheels on the design. Regardless, my assumption
that the launcher was a temporary solution is mirrored by the reports from that time.
While there is no confirmed combat usage of this rocket by the Japanese at least one does seem to
have been used against its former masters. While digging in the online archives I managed to find
these photos which show American troops firing a rocket at the Japanese supposedly on Hirohito's
birthday. The launcher appears to be the same type as the one used for the test launch. This
may be the initial launch following the capture of the rockets with the other photo possibly showing
the later Aberdeen tests. 85 rockets were captured just in the Manila area which show
that this project had been under development for some time and was not just a last minute
weapon by the troops on the ground, but it is not known if they were actually used against
Allied forces. Considering that a rocket-propelled projectile completely destroys itself upon impact
and that any number of other projectiles could be hitting allied positions at any given time
there is a decent chance one of them could have been a massive rocket. Without any proof of this
though it is merely speculation whether or not it did occur. From the testing done after their
capture the crater created by the blast of one of the 447mm rockets was similar to that of a
U.S 1,000 pound bomb so it certainly could have done some damage. Similar to many other things
about this project the accuracy does not seem to have been heavily documented. In total the
U.S conducted 3 tests including the 1 tested in the Philippines, it is unclear if the previously
mentioned birthday present for Hirohito was one of these tests of a separate launch. Given it
doesn’t mention anything about a test in the photo's caption this could indicate it was a
4th launch but it is impossible to say without further information. Either way that first test
in Manila did reveal what may have been a design flaw in the weapon. The rocket appeared to launch
well and flew fine until the end of its flight where it began to wobble badly. This was likely
caused by insufficient spinning produced by the rockets and could have affected accuracy
at longer range. One thing worth considering is that this first launch was estimated to be
about 6000 feet with the latter 2 launches only being launched 5000 feet. These rocket
projectiles more than likely were intended for shorter range engagements so perhaps a range past
5000 feet was more than the designers intended. Unlike many other seemingly outrageous projects
by the Axis powers these Japanese rockets actually represent a fairly economic solution
for their lack of artillery. They likely had next to no real impact on the war but had Japan begun
development even just a few years earlier could have proven to be another deadly addition to the
Japanese arsenal. The outcome of the war would still have been an Allied victory though the
casualties suffered may have been slightly higher. So what do you think of this massive rocket? Let
me know in the comments and also let me know if you like these sorts of topics which may be a
bit crazy or cursed but don’t directly relate to tanks. As always a huge thanks to both Kamikoto
for sponsoring and to my Youtube members for supporting my content. Don’t forget to
check the link below to save $50 dollars on your order. To everyone else thank you for watching,
if you’re not sure what to watch next check out the videos popping up on your screen now or click
on my channel and see if there is anything that catches your eye. Hopefully I’ll see you there.