An Old Projectile, Some Ancient History

You never know what you’re going to find on GunBroker. We found this unusual WWI Stokes Mortar cartridge, or really, projectile; and got, thanks to the seller’s description which is reposted below, an education on the human drama of the introduction of a weapon we’ve always taken for granted, the muzzle-loading infantry mortar.

stokes01

The seller explains (edited for brevity):

This is a part of very large collection I have bought in Miami. 81 mm inert Word War I British Mortar with all original paint. Please, read the history behind this munition development and deployment. The Stokes mortar was a British trench mortar invented by Sir Wilfred Stokes KBE that was issued to the British, Commonwealth and U.S. armies, as well as the Portuguese Expeditionary Corps (CEP), during the later half of the First World War.

The 3-inch trench mortar is a smooth-bore, muzzle-loading weapon for high angles of fire. Although it is called a 3-inch mortar, its bore is actually 3.2 inches or 81 mm.

Ha! Mortarmen of the world, that number ring a bell?

Near as dammit, 81 mm.

Near as dammit, 81 mm.

Frederick Wilfred Scott Stokes – who later became Sir Wilfred Stokes KBE – designed the mortar in January 1915. The British Army was at the time trying to develop a weapon that would be a match for the Imperial German Army’s Minenwerfer mortar, which was in use on the Western Front.

Success, right? Not so fast:

Stokes’s design was initially rejected in June 1915 because it was unable to use existing stocks of British mortar ammunition, and it took the intervention of David Lloyd George (at that time Minister of Munitions) and Lieutenant-Colonel J. C. Matheson of the Trench Warfare Supply Department (who reported to Lloyd George) to expedite manufacture of the Stokes mortar.

The Stokes mortar was a simple weapon, consisting of a smooth bore metal tube fixed to a base plate (to absorb recoil) with a lightweight bipod mount. When a mortar bomb was dropped into the tube, an impact sensitive primer in the base of the bomb would make contact with a firing pin at the base of the tube, and detonate, firing the bomb towards the target.

Yes, they take shotgun primers.

Yes, they take shotgun primers.

The barrel is a seamless drawn-steel tube necked down at the breech or base end. To the breech end is fitted a base cap, within which is secured a firing pin protruding into the barrel. The caps at each end of the bomb cylinder were 81 mm diameter. The bomb was fitted with a modified hand grenade fuze on the front, with a perforated tube containing a propellant charge and an impact-sensitive cap at the rear. Range was determined by the amount of propellant charge used and the angle of the barrel.

stokes-mortar-sketch

A basic propellant cartridge was used for all firing, and covered short ranges. Up to four additional “rings” of propellant were used for incrementally greater ranges. The four rings were supplied with the cartridge and gunners discarded the rings which were not needed. One potential problem was the recoil, which was “exceptionally severe, because the barrel is only about 3 times the weight of the projectile, instead of about one hundred times the weight as in artillery. Unless the legs are properly set up they are liable to injury”.

Several other kinds of mortars were tried by the various belligerents during the Great War: breech-loading mortars, rifled mortars, spigot mortars, and the French even made compressed-air-powered mortars. But the simplicity, portability and reliability of the Stokes was the category winner. While some of the above technologies found their way into World War II weapons, the majority of mortars then and now are on the Stokes model.

stokes_mortar_trench_placement_diagram

The original Stokes had the benefits of simplicity and easy manufacturing, but it lacked things we now associate with this class of weapon: a fin-stabilized (or, in rare case, rifling-spin-stabilized) projectile for higher accuracy, a removable booster charge for selectable longer range, and sights. (You might ask, how does one use sights on a mortar or other indirect fire weapon, where by definition you can’t usually see the target? As one hears about relationships, “It’s complicated.” It would be a good subject for a later post).

stokes5

Mortars today are all descended from the humble Stokes, and they grew those capabilities mentioned above after the Armistice.

A modified version of the mortar, which fired a modern fin-stabilised streamlined projectile and had a booster charge for longer range, was developed after World War I; this was in effect a new weapon.

The projectile and all its history can be yours, if you follow the link to the GunBroker auction. For more information on the genesis of the 3-inch Stokes, including even a (grainy) picture of Stokes His Ownself, check out this great excerpt from a book by Bruce Canfield.

11 thoughts on “An Old Projectile, Some Ancient History

  1. DSM

    Hognose, a question for clarity’s sake, your note states: “…but it lacked things we now associate with this class of weapon:…a removable booster charge for selectable longer range…”
    Further down it states: “Up to four additional “rings” of propellant were used for incrementally greater ranges. The four rings were supplied with the cartridge and gunners discarded the rings which were not needed.”

    Am I reading this right or just not understanding the nuances of a vintage projectile thrower?
    The AF deleted the mortar capability shortly after finally shelving their M29s and getting the M252s. About my only experience with either was helping carry the rounds and helping build the pits during exercises. I do remember they sounded nothing like the subtle “boop” in the movies!

  2. Boat Guy

    One of my favorite discoveries in researching my paternal GrandDad at NARA was some correspondence to the CO of the Trench Mortar Battery in the 60th FA Brigade. That CO (a Captain) must have been a helluva guy; seems a liberty party (after the Armistice) was on a train returning to the unit. The train happened to stop in the town where the Battery was quartered but because that town was not the terminus of the train run the OIC of the train told the Sergeant in charge of the liberty party they had to ride on to the end; in essence giving them leave to report late to the unit, and an extra day or so of liberty. The Sergeant said “To hell with that, we’re getting back to our outfit” and took his guys off the train. The train OIC griped to the CO who had to “Reply By Endorsement”.
    There were several other pieces attesting to what a good Battery that was. One of the Battalions in the Brigade … not so much – saw where the BC put the Battalion CO on arrest-in quarters. The other Battalion (129th FAB) was Harry Trumans and was by all accounts a damn fine one.

  3. gbob

    I would love to see a post describing mortar aiming. I had done a small amount of reading a few months back on the subject, firing tables and a lot of raw data is available online. But like an open book math test, if you don’t get it, the book doesn’t help.

  4. morokko

    Side note, apart from French, the biggest enthusiasts of air powered artillery during the WWI would be Austro-Hungarians. They used whole family of Luftminenwerfer – air powered mortars, from tiny man portable 80mm guns to heavy 200mm calibre pieces. Those Habsburgs must have had lasting and tender feelings toward airguns, since their deployment of about a thousand Girandoni repeating air rifles during the last decades of XVIII .

  5. Sando182

    ” the French even made compressed-air-powered mortars.”
    Pneumatic powered fireworks are a thing. Can’t be alot different than air-powered mortars, could it?

    (You might ask, how does one use sights on a mortar or other indirect fire weapon, where by definition you can’t usually see the target? As one hears about relationships, “It’s complicated.” It would be a good subject for a later post).
    Definitely. I’ve always wondered about that.

  6. Neil S.

    Finally, something I actually feel qualified to comment on! I may have been the only man to have ever enlisted with the specific desire to work in a mortar platoon FDC section. (I got a really confused look from the recruiter.) For anyone who wants to get into detail about how mortar fire control works, at least until summarized by our host, you’ll want to look up FM-90 Mortars and FM-91 Mortar Gunnery.

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