Inside The Chieftain's Hatch: Ho-Ro 

Those "mini engines" sticking in front of the engine are mechanical injection pumps, used mainly on old diesels, superceded by electronic. Were also rarely used on petrol engines, to bridge the caburated and EFI ages.

Years ago I read an account of an Australian constabulary unit's experiences on postwar occupation duty in rural Japan. They quickly learned that they had to patrol in jeeps because there wasn't one bridge in their entire operations area capable of carrying the weight of a six ton Staghound armored car. It's hard to develop much of a tank arm when you can't even deploy them in your own country. As for the Aussies this actually worked out for the best because their role quickly evolved from occupation to befriending the locals who were pleasantly surprised when the terrifying "foreign devils" turned out to be a bunch of smiling young men in jeeps handing out relief supplies and candy.

Take it from a retired mechanical engineer, the 2 devices you were looking at were fuel injection pumps for the engine. Talk about tight packaging and the absolute fact they didn't talk about tanks very much from their axis ally....

Huh. Incredible. I had no idea that a HO-RO actually survived. Definitely gonna be checking this out. Thanks for showing this off.

Direct fire for a divisional SP artillery piece makes sense if you stop and remember that most Japanese tanks were light with small caliber anti-tank guns. A large caliber assault gun is really useful when the tanks around you are armed with 37mm, 47mm, or low velocity 57mm main guns. The Type 97 Chi-Ha only had between 8mm to 25mm (on the gun mantlet) of armor, and it was classed as a medium tank by Japan.

The contraption at the back of the "cab" is the fuel injection pump, used to correctly time when fuel is injected into the cylinders, it will be mechanically connected to the engine crankshaft, which turns a cam shaft, followers on the cam open and close the fuel valves to release a pulse of deisel to the cylinder at the right time.

Yep, those are mechanical injector pumps. If you look closely inside the engine compartment, you may notice coils and zigzags in those lines so that they are exactly the same length.

When I worked at the Air/Ground Museum in Quantico I was very eager to tackle the restoration of this vehicle. I had spent thousands of hours on a ZIS-3 artillery piece and an SU-76. Restoring the SU-76 was a great deal of work but when I was short-toured and PCS'd the hull and gun were blasted, painted and restored. The engines had been torn down, restored and painted. We decided to "pickle" the engines (2 flat-head, 6 cylinder, gas engines in tandem) because it had thrown a rod in the forward engine due to holes in the oil pan (probably caused by the vehicle running over a mine). I'm disappointed that no one tacked the restoration of this Ho-Ro since it is probably the only intact specimen of the breed. I have wondered for 30 years what became of this Ho-Ro and I'm delighted that she is now in a climate controlled environment.

At 7:12, as the cotter pin is usually a softer metal than what it passes through, a likelier expedient method of removal is to shear the cotter pin as the track pin is pounded out with a hammer and drift.

The Japanese armor of the day tended to shatter over time. On the Aus Armor page they are digging up Grant tanks of a similar age with no shattering. Thanks Chieftain and WOT!

Mechanical fuel injectors/pumps are your mystery Mini engines. You'd find those on diesels all the way through the 80s when modern tech allowed those comtraptions to be fitted directly to the injectors or to a series of rails. Fairly advanced tech for the 40s in a diesel. Heck, it looks very similar to some of the pumps I've seen on CAT motors from the 80s and 90s except they're mounted remotely.

This is a rather rare Japanese SPG, to find one in a states side museum is nice. Ruff condition but mostly there.

Ah, Yes, the Japanese Derp gun. Edit: "We can't get the hatches open" WD-40: You dare challenge me, Mortal?

Added that museum to my bucket list thanks to your video and glad to say I made it there last august. Was amazing!!!

13:35 I see a logical reason. If the one closest to the rear was horizontal the dirt and rock tracked up is far more likely to trap between the rods and get channeled into the spring as it falls verses hitting the top rod and getting shed to the side. Pretty simple actually. That's a rock funnel into the spring they did away with by making it vertical to the falling dirt and mud. Plus that configuration is far stronger being compresed into the spring at the geometry it moves going in on that pivot.

I am so glad that throughout the wars we have had some out of the bunch that thought "we need to keep this to study", and even more glad that a few thought "for future generations to see", instead of scrapping them.

About the pin securing the tracks: caught pinsamt that split apart have been common on various farming equipment thru the years. At least on a farm, doing a field repair out on a field they can be something that creates opportunity to be inventive with strong language.

This thing looks like it wouldn't be out of place in a Metal Slug arcade game. Like the whole design with the bolts and rivets everywhere, the top heavy structure, semi-exposed crew, the sheer cartoony look of the thing :P

This is one of the most interesting videos you've done chieftain, explaining your educated guesses and the different designs to other tanks.

old tech is great for my education into mechanical engineering, once again, nick teaches me more about tanks and little things engineering wise than anywhere else* *excluding the tank museum.

Type designations actually had two different possible systems - some were named based on the year of the current reigning emperor as you mentioned, but sometimes they were done based on the last two digits of the traditional Japanese calendar year, which has a year 1 in 660 BCE. This just adds to the confusion of the designations leaping around.

I’ve spent more time than I care to admit looking at footage and animations of the bell cranks suspension on ha-go and your explanation is what made it make sense 😅

The Japanese used a log for elevation fired a smoke round and took radio corrections from forward observer they were rather well organised

Since most Japanese tanks had smaller caliber weapons it may have been for use against fortifications and dug in infantry.

The injector pumps are most likely run off the cam drive at one end of the engine which is why they are located where they are

Respectfully, the Ho-Ro might have been a very powerful weapon in the Japanese Army because Japan was just putting 47 mm guns into their tanks in 1944. Also, Japan had relatively few field radios, so indirect fire wasn't going to happen much, if ever. My guess is they planned to keep this artillery piece behind the tanks, firing ahead of them as they advanced. On the plains of China, no one was going to be killing the enemy from 2000 meters, but also not fighting at point blank range.

The US Navy technical reports on Japanese tank armor was that they were high hardness to get ricochets from small arms, antitank rifles or low velocity 37mm cannons. The Japanese made high hardness AP shells for there 47mm to deal with Soviet armor which had similarities in terms of hardness. First generation cast Sherman’s proved to be fairly vulnerable to the 47mm under 500 yards as a result.

I go to this museum at least twice a year the HO-RO and Abrams from the USMC museum are always great to see

Also, the thing you didn't know for certain what it is: your guess are correct - it's the diesel injection pump. It's a bit of odd looking compared tol for example, a 60's Land Rover.

The spring set up is similar to the suspension on a Citroen 2CV (which accomplished largely the same with a hydraulic cylinder).

The direct fire only mode is a feature, if one looks at how small Japanese tank guns were generally. These things cracked anything too tough for the popguns on the tanks to handle. .Eggshells armed with Hammers

They’ve put the diesel injector pumps in the cab so they are easy to bleed under fire. The thought being bad fuel. Only way to clean the filters is to disassemble and unfortunately let air in, but the high pressure pumping pistons won’t pump air.

It is very curious to see a Welin breech gun on an armored vehicle. I always like seeing close ups of them

Later, they were able to open the 3 hatches. they found three Japanese soldiers waiting to attack the American devils. After a short battle, the Japanese drove off in victory.

Hi-Ho, Hi-Ho it's off the Ro we go... 0~o sorry, low hanging fruit and all. ^~^ 20:22 mark, these are indeed two sets of mechanical fuel injectors. A like type fueling system is used on my grandfather's Ford 4000 diesel tractors engine.

I've always had a soft spot for Japanese armor, simply due to the scarcity of it. we just don't know enough about it to be certain in a lot of regards.

Self propelled Caronade perhaps? Would have made sense for bunker busting, like the original (short barreled) StuG.🤔

The accelerator bank looks a lot like a modern diesel injection system. I've seen similar on modern Diesel engines

The Heritage museum! I love that place it is gorgeous in Hudson, Massachusetts. Very fun and gorgeous layout.

Maybe like an M113 A1 - main steering levers and pivots. And yes - injector pumps. Would have had a cover.

That museum is epic!! So glad I'm only 40 mins away 😊

@♦20:30. Those fuel injector pumps, what I like is that there 2 units, 1 for each bank of cylinders. Probably they had a 6 cylinder version and just decided to keep it simple for engineering. Those things were still in use wit truck diesels in the 90's.

Finally after more than 15 minutes of waiting we get to the track tension! This is clearly the high point of every tank video! ❤ I also want to on a more serious note say a big thank you for bringing this to us! 😊 And cool in a way that it is basically like a research mission as well where we can all take part!❤

Finally a video on the Type 4 Ho-Ro ! It doesn't seem to be anyone doing a detailed video on this thing. This makes me wish that they send you to Japan and do more video on their vehicles especially the another only surviving Type 3 Chi-Nu or the only functioning Type 89 I-Go medium tanks. Or even videos on the Type 61 MBT which they should allow you to go inside and filming since it is retired for at least 2 decades now, not sure about Type 74 eventhough it is slowly being replaced by the Type 16 MCV.

It's a pity that Japan doesn't have a tank museum, so detailed information about tanks is not preserved.

It's odd, no one seems to have mentioned that the HO-RO does not have a Chieftain's hatch, in fact, it came out way before the Chieftain, so it would be extraordinary for it to feature a hatch from one.

Thank you very much for the explanation on how the suspension work. I've seen it for years, and was never quite sure what was going on. Now it makes sense. I've had cotter pins on a heavily used 6 and 1/2 horsepower rear tined Sears rototiller. I use it in clay soil. Getting both wheels off can be lightly annoying, especially if you've just discovered the clay is too wet 5 in down to properly tine, but it's gooped onto everything. That's just two cotter pins...

RU-vids algorithm just sent this to me, I was just at that museum it was a blast and the staff are all rather knowlegable I got to have some really great conversasions about several of the pieces on display.

What an outstanding hands on explanation. Great Job Sir.

Perhaps the direct-fire capability makes more sense if you look at this as a coastal defense weapon? I would imagine that this thing would do a number on most landing craft.

Outstanding video and presentation.

from what ive seen and read, especially in hara's own books, in the driver's position the center lever is a parking brake, the two for each side are individual brakes and clutches, they have a ratcheting mechanism with a button to release on top, and then theres the levers for the 4 speed transmission and directly behind that for the 2 speed auxiliary transmission, essentially a high/low range, giving it 8 forward speeds and 2 reverse. those units on the engine firewall were injector pumps theyre driven on gears off the camshaft.

There is a beautiful type 97 in the war museum in Tokyo.Great video, very clear.

Neat, a driven mechanical fuel injection pump. The adverse of the era being Unit Injection like a Sherman's Detroit where each injector is it's own mini injection pump ran directly off the cam, this thing is more akin to a early 5.9 cummins in a eighties dodge pick up in fuel delivery with a high pressure lines to each injector ran off a injection pump.

I’ve been to the American Heritage museum in Hudson for their tank Demonstration weekend. I loved it

1:51 "We had this habit of blowing up" PMSL

Great video, Nick.

19:59 The term you were looking for is "sections of angle iron". Loved the video. 👍

Very interesting and nice format

Would it be worth you getting one of those inspection cameras with the light?

Considering by 1944 Japan was fighting a defensive war, I can see these being used in fixed positions, where the mobility was just needed to move from one prepared position to the next, if the were part of the Navy's island defense. If they were in China, no clue.

I suspect the second set of tillers for steering may be used depending on what the tank is doing. IE, one for steering while in placement for aiming while the other one is used while driving

Thank you. It is always good to see Japanese armour getting some coverage, as it is often overlooked. In fact, the whole of the Pacific and Far East are generally overlooked due to the emphasis on Europe and North Africa.

6:36 man that rising sun on the side of it has gone full super nova hasn't it lol

Hey Chief, 20:30 is a high pressure fuel pump with cam supply, governor etc, direct supply to the injector head via those metal hoses.. BMC used the same on their 2.2s... Mad to put it there though.

Amazingly good animation of the movement of the bogies at 11:15.

The Type 4 Ho-Ro (四式十五糎自走砲「ホロ」) is an open-topped self-propelled gun with a short-barreled 150 mm howitzer, based on the Chi-Ha. Being pressed instantly into service on its creation, a dozen or so were shipped to the Philippines together with the newly formed 1st Self-Propelled Artillery Company. While it did see combat with several confirmed Sherman destructions, it was effectively used in close-quarter combat rather than as an artillery piece, firing at Shermans at 100-200 m range in smokey and low visibility scenarios, and repositioning on each shot. Arriving in Dec 1944, the last Ho-Ro squad served until knocked out in Mar 1945 with the remainder of the company fighting until the end in the mountains as regular infantry. Armour type: Rolled homogeneous armour Armour Front Sides Rear Roof Hull 12 mm (80°) Front glacis 15 mm (63°) Joint plate 25 mm (37-64°) Lower glacis 25 mm (28-36°) Top Left 25 mm (25-26°) Top Right 20 mm Bottom 17 mm (70°) 20 mm (4-69°) 8.5-12 mm Turret 25 mm (15°) 20 mm (0-11°) N/A 12 mm 150 mm Type 38 Mode Capacity Vertical Horizontal Arcade 28 -10°/+20° ±5° Ammunition Penetration statistics Ammunition Type of warhead Penetration @ 0° Angle of Attack (mm) 10 m 100 m 500 m 1,000 m 1,500 m 2,000 m Type 95 APHE APHE 38 37 35 33 31 31 Type 92 HE HE 55 55 55 55 55 55 Shell details Ammunition Type of warhead Velocity (m/s) Projectile mass (kg) Fuse delay (m) Fuse sensitivity (mm) Explosive mass (TNT equivalent) (kg) Type 95 APHE APHE 290 36.1 1.2 19 2.6 Type 92 HE HE 290 36 0 0.1 7.02 As part of the technology sharing scheme between Nazi Germany and Imperial Japan, the Japanese Army delegates were shown many German vehicle designs. These included the Grille series of self-propelled guns. This is what the Japanese Army Technical Bureau would base the Ho-Ro on. Like the German Grille, the Ho-Ro was based on an already existing tank chassis. The chassis chosen was that of a reinforced Type 97 Chi-Ha. Production of the vehicle would fall to Mitsubishi Heavy Industries.The armament of the Ho-Ro was the Type 38 15 cm (5.9 in) howitzer (三八式十五糎榴弾砲 Sanhachi-Shiki Jyūgo-senchi Ryūdanhō), which was also based on a German design by Krupp. The gun had previously been withdrawn from service in 1942 as it was deemed outdated, being a 1905 design. The surplus guns were brought back into service and mounted on the Ho-Ro. The ammo of choice for the Type 38 gun was the Type 88 APHE (Armor-Piercing High-Explosive) shell. It could also fire HEAT (High-Explosive Anti-Tank) if necessary. The gun was capable of firing one of these 36 kg (80 lb) shells at 282 m/s to an effective range of 6,000 m (6, 542 y). Ammunition was stored in a container on the engine deck. The 15 cm howitzer was mounted behind a 25 mm (0.98 in) gun shield and had a limited traverse arc of 3 degrees left and right. It could elevate 20 and depress 10 degrees. The gun shield was the only real armor on the vehicle. The 6 crew members of the Ho-Ro were completely open to the elements, small arms fire, and shrapnel. The vehicle also had no close-defense machine guns. Mitsubishi produced a small number of these self-propelled guns, a meager number of 12. The Imperial Japanese Army rushed these into service during the last months of WWII in the Philippines Campaign. They served in batteries of 4 with the Japanese 14th Area Army. Remaining units were stationed in Okinawa during the American assault. However, they were grossly outnumbered by the United States’ own artillery units.

I've been to the AHM and seen this! My group donated an Arisaka to the collection...which is awesome!

For Marine logistics references, how many cases of beer could it hold?

I kind of wonder if this was more built as an ad-hoc tank destroyer with what large caliber guns they had lying about in storage than as a real assault gun. In 44, as someone else points out, they were starting to encounter Shermans and discovering that their 47mm and 57mm main tank guns were not reliable Sherman stoppers. This may have been their quick and dirty solution to pump out more TDs using stuff they already had.

Hey, I was at that exact museum about 2-3 weeks ago! I saw that exact Ho-Ro.

Love all the videos.Learn lots about ww2 armor.

Woohoo, I'll check this out next week! I live near this museum!

Always love the idea of spgs. Take a tank we already have, remove turret and/or hull and slap on the largest gun possible without wrecking the suspension.

26:14 honestly the whole thing reeks of a pillbox buster lol

Think what the industrial capacity and material it took to make the Yamato, Mushashi, and Shinano and invested that into aircraft or armored units. Thankfully they didn't, but it wasn't beyond their capability.

It looks like the tensioner locking lever would depress when the tensioning tool was in place, neat setup.

just a thought on the track tension system . I would expect it uses a worm gear system, and thus you only need to stop it turning via vibration so that small latch would be enough and the smaler size of the square drive would also lean towards it using a worm drive as less torque would need to be applied by the chap and his spanner.

Let's gooo new Chieftain's Hatch video just dropped

Would love to have this tank in the game as a TD. Even as a SPG would be nice. Just because there is not enough tanks to make a tech tree line doesn't mean it shouldn't be added.

Great museum!

本車に搭載された照準器は直接照準射撃が可能なものであり、ベースには九七式五糎七戦車砲用の照準眼鏡を用い、焦点鏡目盛を交換した。これは3,000mまで照準できる縦目盛と、左右各100milの方向目盛が刻まれたものである。また、間接射撃用として車長が使う照準眼鏡があり、これは三八式十五糎榴弾砲の既存装備品であった。方向射界（旋回角）は左右3度、高低射界（仰俯角）は-10度～+20度、後座長は590mmであった。砲弾は戦闘室および機関室上部の砲弾箱にそれぞれ搭載された。搭載弾数は車内16発と後部車体上の弾薬箱に12発の計28発である

Very interesting video on this Japanese self-propelled RO-HO but perhaps putting some oil and grease here & there would have helped a bit 😂

From what I understand, there is a cargo ship sunk by a US submarine, that carried armoured vehicles on its way to the Philippines among which the Type 4 Ho-Ro was present. Too bad they won't consider financing recovering some of those vehicles, although I wonder in what condition they would be after nearly 80 years down on the bottom!

To be fair to the Japanese, the BEF could certainly have used some of these at Arras in 1940. So even without an indirect fire capability they could have been useful in the right situation.

Yes as a master diesel mechanic, those mini engines are injectors pumps. They meter and injector the fuel into the engine, very much like the pump on a 5.9 cummins.

5:56 which is ironic where you think about where the base material for rubber comes from lol

Well. Atleast there were never columns of them rolling down the streets of Los Angeles, San Francisco, Portland, or Seattle.

"There's an Irish expression, it's been through the wars." That's also a Scottish and English expression.

Love this museum.

I love the animation ❤

Me starting the video: sucks ill never get to see this up close Me two minutes later: oh its 45 minutes from my house

I guess at 1944 Japans artillery doctrine was ''anything within 500 meters''.

25:44 i mean so long as it delivers the high explosive to where you want it... or close enough is anything really obsolete same goes for bullets too i guess after all the mechanical contrivances may have got stronger and tougher and lighter over the years but humans are pretty much as squishy now as they were 1000 years ago

Up at Collings I see! American heritage is a great collection.

Ho-Ro Chieftain! It's good to see you too 🙂

"There isn't enough elevation for indirect fire" In my mind, I then heard an English voice say; "But that's how they did it..." xD

Its a system like the PzI with the SiG33, a way of making mobile a big cannon to support frontline units

No one here plays wot anymore we just love the chieftain and these vids

The behavior of the undamped suspension of the running gear when driving off-road may have been interesting, but it will probably have been even more interesting after firing the gun.