Japanese weaponry

Firing a ‘knee’ mortar.

When it came to weapons production, the Imperial Japanese Army’s requirements often came in second to the needs of the Imperial Japanese Navy. The Army was an infantry-heavy organization that lacked much in the way of the modern heavy weaponry other armies enjoyed. 

To help compensate for the lack of heavy weapons, the Imperial Japanese Army worked hard to develop large numbers of what were probably the best light infantrymen in the world at the time. Their creed stressed relentless offensive action seeking a quick decision and emphasizing spiritual factors including zealous dedication and fighting spirit. Night attacks were a true specialty, and their weaponry reflected their light and fast doctrine.

To offset their frequent lack of artillery, the Japanese augmented their firepower through the extensive use of mortars, the best and most cost-effective substitute for industry-intensive heavier artillery.  Technically, Japanese light “knee” mortars at first merely bridged the gap between hand grenades and true mortars and were more properly referred to as grenade dischargers.

The Model 89 was by far the most prolific of the grenade dischargers and the weapon most commonly encountered by Allied Marines and soldiers throughout the various theaters of the Pacific War. Technically known as the Hachikyu Shiki Jutekidanto, or 89 Model Heavy Grenade Discharger, the new weapon featured a wide variety of improvements over the old Type 10 and had almost universally replaced the former weapon by 1941. To the frontline Japanese infantryman, the Type 89 was most often referred to as the Juteki.

To fire, the gunner removed the fuse’s safety pin and dropped the bomb tail first down the muzzle of the knee mortar. A pull on the leather lanyard attached to the trigger then fired the weapon. The firing pin struck a percussion cap primer that fired the propelling charge, which also caused a copper driving band on the charge body to push out and engage the rifling of the barrel. The force of discharge also set back and armed the fuse in the nose projectile and re-cocked the mainspring inside the mortar.  This was usually done at a 45-degree angle.

Despite these relatively crude controls, a soldier could quickly and easily be trained to fire the Type 89 knee mortar with impressive accuracy. While it could be fired by one man, a knee mortar with a three-man crew could maintain an effective rate of fire of 25 rounds per minute.

 Lt. Col. Merritt “Red Mike” Edson, leader of the famous Marine Raiders, critically evaluated the knee mortar and insisted American forces badly needed an equivalent. He listed the following reasons:

“1. It is a one man load.

2. A man can carry ten rounds on his person besides his weapon.

3. It has a high rate of fire.

4. It gives to the platoon commander a weapon of this type which is immediately available to him.

5. This mortar uses the Jap all-purpose hand grenade….”

A Marine Corps legend, then-Lt. Col. Lewis “Chesty” Puller seconded Edson’s opinion. “I consider it imperative that the Army and Marines be equipped with knee mortars and only carry one type grenade.”

Army Sergeant C.W. Arrowood completely agreed: “The Jap knee mortar gives us hell. They come in fast, thick, and accurate. Can’t we have one?”

M79 40mm grenade launcher

The answer to Sergeant Arrowood’s question was a resounding No. United States forces soldiered on with the little loved rifle grenade until the advent of the M79 40mm grenade launcher during the early stages of the Vietnam War.

References: Warfare History Network;

Click on images to enlarge.


Military Humor – 

You can always count on your scoped grenade launching silenced pistol bipod w/ attached katana handle crowbar!

Because no Zombie Apocalypse survival kit is truly complete w/out a grenade launcher & a few bandoleers of HE rounds.



Farewell Salutes – 

Cecil Akigg (100) – Calgary, CAN; RC Army, WWII, ETO, radar technician

Nicholas Baxter – Harrisburg, PA; US Army, Co. M/187th/11th Airborne Division

Benjamin Bold – Rotorua, NZ; NZ Army # 267128, WWII, Pvt., J Force

Jean Doyle – Tyngsboro, MA; US Army Air Corps WAC, WWII, 1st Lt.

Luther Gordon – San Diego, CA; US Army, WWII, ETO, Purple Heart, Silver Star

Melton ‘Dale’ Hair – Tulsa, OK; US Navy, WWII

Herschell Johnson – Dothan, AL; US Army, WWII, ETO, 8th Armored Division

John Kelly Jr. – Billings, MT; US Navy, WWII

Richard Pettijohn – Naples, FL; US Army, WWII, ATO, radio operator

Gordon Sherwood – Yarmouth, ME; US Army, Korea


About GP

Everett Smith served with the Headquarters Company, 187th Regiment, 11th A/B Division during WWII. This site is in tribute to my father, "Smitty." GP is a member of the 11th Airborne Association. Member # 4511 and extremely proud of that fact!

Posted on January 29, 2018, in WWII and tagged , , , , , , , , , , , . Bookmark the permalink. 91 Comments.

  1. I saw a lot of these during my trip to Mount Samat, Bataan. It’s fascinating. It would be better if someone would explain how the weapons work though.

    Liked by 1 person

    • I hope you don’t mean to try one of those you saw! but here you go… A Grenade Launcher (GL) is much like a light infantry mortar. The round
      is like a large bullet, with the projectile and the launching charge
      contained in a single unit. The launcher is like a pistol with a light
      mortar barrel.


  2. I knew only a bit about this weapon. Your article piqued my curiosity; I took this excerpt from Wiki – (they produced this nasty device in 1932!)

    When fired from the Type 89 discharger, the Type 91 fragmentation grenade was fitted with a propellant base and time fuse. It did not explode upon contact, but was designed to ignite its fuse while in flight. A weak creep spring inside the grenade firing mechanism allowed the firing pin to be thrown back upon launching, igniting a time fuse with a 7-8 second delay. Using this system, the Type 91 grenades could be launched through jungle cover or through small openings without the danger of premature detonation in the event the grenade struck an object on its way to the target. Although the Type 89 could be fired by a single person, it was typically operated with a crew of 3, enabling it to reach a rate of fire of about 25 rounds per minute.
    Good posting, GP.

    Liked by 1 person

  3. How is you 😀
    I found a perfect IMAGE which is perfect Naughty on my the end of the month blog.

    Liked by 1 person

  4. GP, Thanks for visiting my website today…..causing me to take a look at your latest here. I lucked out reading & fascinated by this piece on the Japanese mortar, more accurately Type 89 knee mortar. I could really identify with this. Our basic training in the Vietnam era included training in firing mortar launchers.You said here how the knee mortar was amazingly accurate. But we couldn’t hit the tank put out on the firing range for us as practice with the mortar launcher!!! You can’t underestimate the skill of the Japanese besides the accuracy of the weapon. Great piece of writing, GP! Phil

    Liked by 1 person

  5. That was truly interesting, GP. I liked seeing the diagrams too. Have a wonderful Wednesday. Hugs.

    Liked by 1 person

  6. Succinct article GP – I’ve not heard of a knee mortar before seeing this post.

    Thank you – keep ’em coming.

    I meant, the weapons articles – not the mortar grenades 🙂

    Liked by 2 people

  7. They should have listened to the sarge, the man in the field, he knew what was needed, trouble with bureaucrats and pen pushing desk officers

    Liked by 1 person

  8. I am not sure how true it is but I read or heard about American GI’s taking the knee mortar name at face value and getting broken legs as result of trying to fire them from their knees

    Liked by 1 person

  9. Ondanks ik helemaal niet van wapens houdt geef je hier toch hele goede uitleg

    Liked by 1 person

  10. I had to laugh part way through it. The Colonel quite the way you do!! Thanks for adding all that and taking the time!


  11. P.S.
    Don’t publish this comment here. It’s unrelated to Japanese weaponry.

    Liked by 1 person

  12. Great post! The zealous dedication part about the Japanese was especially interesting!

    Liked by 1 person

  13. Interesting. We certainly underestimated the Japanese in the early days of WW2 – and I wonder how much a lack of respect for your enemy is behind an unwillingness to learn from them?

    Liked by 1 person

  14. There is an excellent PBS program on the development of radar (also, a critical weapon during WWII). It’s called “The Secret of Tuxedo Park”. You can find details at: http://www.pbs.org/wgbh/americanexperience/films/secret-tuxedo-park/.


    • I’d heard of Tuxedo Park, but never knew the details. I skimmed the transcript and sign up for the newsletter, so I will get back to it. Thank you very much, Anna.


  15. This is a really awesome post, very informative and interesting!

    Liked by 1 person

  16. What a disservice to our troops to keep better equipment from being developed.

    Liked by 1 person

  17. Informative and interesting gp, never heard of the knee launcher before, my only experience has been Mortars with base plate and the M79 Grenade launcher

    Liked by 1 person

  18. I did not know!!
    Thank you for your time and effort.
    You’re awesome. 😀

    Liked by 1 person

  19. Wonder what kind of a kick that had and why my knee is hurting, G… –Curt

    Liked by 1 person

  20. Very interesting… a nice inside look at Japanese weaponry. “It gives us hell… can’t we have one?” Ha 🙂

    Liked by 1 person

  21. An interesting look at an amazing weapon. Thanks, GP.

    Liked by 1 person

  22. The political infighting in the Japanese military was astounding. Had the Imperial Japanese Army and Navy brass cooperated and not competed, their impact on the Pacific may have been even more powerful than it already was. Some of the equipment issues that the IJA had was puzzling. Their tanks were quite frankly terrible. Designs were for extremely light infantry support vehicles like the 7.4 tonne, type 95 Ha-Go, was not even a match for British M3 Grants in the ’44 Burma campaign. Many such examples exist, not least the IJA and IJN persisting with obsolescent aircraft designs as the Allies overtook them in the Pacific theatre (I know they had great aircraft like the Ki-61, Ki-84 and Ki-100, but these weren’t available in anything like the numbers needed). I think the attitude of the Japanese commands of both the Army and the Navy was that the Japanese soldier was their best weapon. They were quite right in that respect. But every soldier, no matter how well trained and motivated needs equipment. Great post GP.

    Liked by 2 people

    • Thank you very much. I agree with everything you’ve said. I can not imagine what would have occurred if the army and navy had worked together (and to think Tojo controlled them both!) His generals and admirals ultimately were one cause for their defeat.

      Liked by 1 person

  23. Thank you, thank you once again.Appreciate remembering….to be kinder and wiser.

    Liked by 1 person

  24. It’s the OTHER blog I write other than Pioneers of Aviation (https://av8rblog.wordpress.com/). Thanks for your support with Pioneers. It is long appreciated!

    Liked by 1 person

  25. Hey GPC, I posted the URL to your article on Japanese weaponry on my blog (http://wonderfulrife.blogspot.ca/2018/01/japanese-weaponry-of-wwii.html). Nice job, brother! AJ

    Liked by 1 person

  26. Very interesting psychology. Incite into their war strategy.

    Liked by 1 person

  27. Very interesting post!
    If you focus on the design (an ignore what is happening to the people on the receiving end), military technology is fascinating. It’s hard to fathom why the War Dept didn’t jump on this knee mortar. They did some things, like the DUKW, with amazing speed.
    I guess sometimes the speed of adoption is a matter of necessity and limited resources, like the Rhino hedgerow cutters welded onto Shermans in WWII, or the “hillbilly armor” for our trucks in Iraq. The Germans in WWII were quick to adopt Czech tanks, and pistols from Poland, Belgium, etc.
    One of my grandfathers mentioned once that when it was his turn to carry a mortar base plate on a hike, that made for a very long day. He would have loved this little one.

    Liked by 1 person

    • I’m sure your grandfather would have jumped at the chance for this one – you can see how simple. The War Dept. had it’s own crew working on new materiels, just as Smitty explained with the tents, haha. They didn’t think about the engineering on those either, but maybe they were insulted to have the Japanese outdo them on this.

      Liked by 1 person

  28. I don’t know much at all about weaponry, but I know enough about bureaucracies and pecking orders to know that, in this case, the power of the bureaucracy outgunned the power of the weapon. 🙂

    Liked by 1 person

  29. An enlightening post about war in the Pacific with engaging visuals.

    Liked by 1 person

  30. red tape is right!

    Liked by 1 person

  31. Since the beginning of warfare great army leaders were willing to learn from their enemies. Here is just one example. The Roman Navy in the early stages of the Punic War with Carthage was vastly inferior to the enemy’s warships. When one of the enemy’s ships got shipwrecked off the coast of Italy, Roman engineers studied its structure and copied the design and built vessels for their fleet that matched the strength of the Punic navy. So it is astounding to read that the Japanese knee launcher was not copied and built for the American infantry men.

    Liked by 2 people

  32. The Army trained its new advisors arriving in Vietnam on almost every infantry weapon available because they didn’t know what the man would find when he arrived at his assignment. When I hit the steel target three times in a row with an M79, you can imagine my delight when it fell from its supports — of course there had been thousands of soldiers hitting it before me.

    Liked by 2 people

  33. That’s an interesting look at a weapon that was indeed versatile, and very useful for front-line troops. Army procurement is notoriously tardy in adopting new weapons in most countries, and suggestions from combat soldiers have been routinely ignored.
    During WW1, it soon became apparent that companies at the front should have many more heavy machine guns. The German successes from using many more HMG than the allies proved this to be the case. But it never happened.
    Best wishes, Pete.

    Liked by 2 people

  34. I so appreciate your help!


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