A Special Contribution Courtesy of
Bruce N. Canfield and Andrew Mowbray Publishers

The Three Inch Stokes Mortar
Excerpted from U.S. Infantry Weapons of the First World War by Bruce N. Canfield


Stokes Trench Mortar Deployed by American Troops

Although mortars had been in use for centuries, they were typically extremely large and heavy siege-type weapons that were not easily transportable. Mortars were curved-trajectory weapons that could lob shells into trenches whose occupants would be unaffected by flat trajectory weapons but, compared to standard artillery, mortars had a relatively short range. The Germans had large numbers of "Minenwerfers" (mortars) ranging from 77mm to 150mm on hand at the beginning of the war, but such weapons are best classified as "trench artillery" since they were not mobile enough to accompany troops. The French and British also utilized some heavy mortars, but these were also relatively immobile and were in the category of artillery rather than infantry weapons.

It quickly became clear that some type of weapon was needed to provide artillery-like fire support to the infantry. While rifle grenades were useful for small-scale work, they possessed insufficient range and power to serve such purposes. A weapon that was fully man-transportable yet could fire reasonably powerful shells at targets beyond the range of rifle grenades was badly needed. The Stokes trench mortar was developed for precisely this purpose.

The Inventor

The Stokes trench mortar was developed by an Englishman, Sir Wilfred Scott-Stokes (18601927) who was the managing director of a mechanical engineering firm, Ransome & Rapier of Ipswich, England. Although Stokes did not have a military background, he quickly grasped the need for a "portable gun" soon after war erupted in Europe. Stokes correctly reasoned that such a weapon would be valuable for reducing the deadly machine gun nests that were beginning to wreak much havoc on the Western Front. Stokes had a working prototype of his trench mortar ready for testing in December of 1914, barely four months after the war started.

Like many notable inventions, Stokes' mortar was ingenious in its simplicity. Stokes' mechanical engineering background enabled him to design a weapon and ammunition that was easy to manufacture and use. The weapon consisted of a smooth bore tube (barrel) 3 inches in diameter with a metal end cap that fitted into a flat base plate. The 51-inch barrel was supported by a bipod that could be adjusted for range. The weapon was broken down into three sections for easy transport the barrel (tube) which weighed 43 pounds, the base plate (28 pounds) and bipod (37 pounds) for a total of 108 pounds.

The mortar fired a high-explosive shell weighing about 11 pounds. The maximum range was approximately 800 yards. Due to exploding fragments, the minimum safe range was about 100 yards. The range was adjusted by varying the amount of explosive propellant attached to each shell (or "bomb") and adjusting the tube's angle of elevation. The mortar was sighted by the simple expedient of lining it up with the target by means of a white line painted on the tube.

The Stokes mortar shell was loaded by dropping a shell down the tube barrel. The shell fired by means of a shotgun-like blank cartridge that exploded when it hit a fixed firing pin attached to the base cap. The exploding cartridge ignited propellant rings attached to the shell. The ammunition used with the weapon was variously termed "shell," "round" or "bomb" in contemporary military manuals.

The Stokes mortar was soon tested by the British Army and was deemed "...a brilliant concept." However, it was determined that the war currently raging in Europe would soon be over and there would not be time to produce the new weapon before the fighting ended! However, these pundits were soon proven dreadfully wrong and in the spring of 1915 the "3-inch Stokes Trench Mortar, Mark I" was adopted by the British Army. However, the production of other types of munitions was perceived as having higher priority, and manufacture of the Stokes mortars and shells was delayed. Eventually, sufficient numbers of these weapons were made and they began to see front-line service by late 1916. The first recorded use of Stokes mortars by the British was near Loos, France, in September where they proved to be very valuable weapons despite the limited numbers available. By this time, however, the British Army had begun to reduce its emphasis on rapidly moving infantry advances in favor of holding static trench positions. This strategy reduced the effectiveness of the highly mobile Stokes mortar and spurred the development of larger and more powerful, but relatively immobile, mortars. Even though the front-line "Tommies" liked the Stokes mortar, the British Army considered it a low-priority weapon and production remained limited.

Such was the situation when the United States entered the war. As we have discussed, the Americans were determined not to become mired in protracted static trench warfare and desired to utilize aggressive, rapidly moving infantry tactics. It was soon realized that the Stokes mortar would be ideal for the Doughboys and the weapon was soon approved for adoption by the U.S. Army. The weapon was known in British service as the "3-inch Stokes mortar," Mark I, and the U.S. Army designated it as the "3-inch trench mortar, Mark I."

There were not sufficient numbers of British Stokes mortars and ammunition to equip the U.S. infantry units, but our allies had agreed to produce the weapon under contract for the American government. The production rate of the British firms involved in Stokes mortar manufacture was not adequate to meet the high demand of the rapidly growing AEF. In order to boost the production rate, approval was granted for the Stokes mortar to be manufactured in the United States. . .

. Most of the 3" Stokes mortars used by U.S. troops during the war were British made. According to a War Department document, the United States procured 914 Stokes mortars from the British for issue to the AEF. Although 843 American-made 3" Stokes mortars were delivered to France before November 11, 1918, few actually made it into front-line combat before the Armistice. The remaining American-made 3" Stokes mortars were used for training purposes stateside. . .

There were two standard types of 3" Stokes trench mortar shells authorized for use with the weapon during World War I. The primary type used was the "Mark I" high-explosive shell. It weighed about 11 pounds, 11 ounces, and was filled with approximately 2 1/4 pounds of "Trojan" nitrostarch explosive compound. TNT was also approved but seldom used. The shell was fitted with the "Mark VI" fuse. The Mark VI was an "all ways" impact fuse designed to detonate regardless of the velocity or angle with which the shell hit the ground. The Mark I explosive shells were painted gray or khaki with a three-inch yellow or red band painted around the body. The shell was equipped with a "safety pin" that was removed prior to dropping the shell into the mortar tube. The "Mark III" practice shell was produced and issued for training purposes. This shell was filled with about 2.15 pounds of sand and a black powder "booster" that produced a puff of white smoke upon impact. The weight and ballistic performance of the Mark III practice round simulated that of the Mark I high-explosive shell. The practice shell was painted dark blue and stenciled in white letters "Practice" on the body.

Three-inch Stokes mortar smoke shells for screening purposes and some white phosphorus shells were tested in limited numbers. There was also some experimentation done with toxic gas shells for the weapon. The 3" Stokes mortar gas shells were usually painted with a pink or green band on the outside of the body for identification purposes. The various types of chemical/gas shells could hold up to seven pounds of chemical compound. This was deemed insufficient, and the 3" Stokes trench mortar was seldom employed as a smoke or chemical agent projector. Therefore, the only type of 3" Stokes trench mortar shell to see any significant combat use was the "Mark I" high-explosive shell. The 3" Stokes trench mortar propelling cartridges used by the U.S. resembled shotgun shells and were color-coded red, green or blue depending on the respective power of the charges. Tables were contained in field manuals that listed the range and "time of flight" according to the type of cartridge and the number of "ballistite" propellant rings that were attached to the shell. Up to four of the donut-shaped propellant rings could be attached to a 3" Stokes mortar shell.

Training in France

It is difficult to overstate the importance of the Stokes mortar. As aptly stated by Konrad Schreier, Jr.:

. . .the 3-inch Stokes mortar revolutionized infantry tactics. It gave infantry a weapon with the power of the basic 3-inch field gun and yet it could be man-carried onto the battlefield.

It was used by every AEF infantry combat division and for training both in France and the USA. At the war's end it was considered an essential infantry support weapon and consideration was given to doubling the number per division.

Certainly, the Stokes 3" mortar was an extremely important weapon for the American troops of WWI. The U.S. Army formed "Howitzer Companies" attached to each infantry regiment. Each howitzer company was equipped with three Mark I trench mortars and three M1916 37mm guns. The official TO&E requirements for a U.S. Army Infantry Division in 1918 was thirty-six 3" Stokes trench mortars. However, if was not unusual for the actual number of weapons used to exceed the official allowance. For example, it is reported that the 42nd ("Rainbow") Division had at least forty-eight 3" Stokes mortars in its inventory by the end of the war.

The 3" Stokes mortar was normally hand carried but some were transported in horse-drawn machine gun carts. The Marine Corps sometimes utilized their Cole handcarts to carry mortars. Some experimentation was done by the Army with mounting mortars on Ford Model-T trucks, but such "mobile mortar platforms" were never used in battle.

One valuable feature of the 3" Stokes mortar was its rapidity of fire. The weapon had a maximum rate of fire of 30 rounds per minute and a sustained rate of fire of six to ten rounds per minute. Sustained firing required that the tube be periodically swabbed out (every five rounds or so) to reduce fouling in the bottom of the tube. Nevertheless, the 3" Stokes mortar could keep up prolonged fire as long as its ammunition supply and the stamina of the mortar men held up.

Numerous contemporary reports and postwar unit histories relate the effective use of Stokes mortars by the AEF. A typical example was related in the book Father Duffy's Story by Francis P. Duffy:

When Colonel Donovan called for the Stokes Mortars to repel the threatened counter-attack on the morning of the 15th, the pieces were set up under the slight protection of the sloping ground, but from this point the gunners could not observe the accuracy of their own fire. So Sergeant Fitzsimmons ran forward to the top of the slope, making himself an easy cockshot for the German gunners while he signaled to his own men his corrections on their aim. He escaped himself by a miracle and had the satisfaction of seeing the shells dropping amongst the Germans who were gathering for the attack, and doing dreadful execution.

The 3" Stokes Trench Mortar

A report from the 42nd Division depicted a rather novel method of firing the mortar:

I took the Stokes and held the barrel between my legs, had one man to load and the other man to help him. Our first shell made a direct hit and caused the enemy a lot of casualties in their ranks. I continued firing as fast as I could with the Stokes... We broke up the counter-attack.

Several dispatches from the 89th Division also contained examples of effective use of the Stokes mortars:

The Stokes Mortar Platoon, under Lieutenant Leedy, went into action at Hois de Mort Marc putting three machine guns out...

In this regiment, one enemy cannon, cal. 88, and its entire gun crew was cut out of action by a direct hit from a Stokes mortar at a range of about 500 yards.

It was found that the moral effect of fire from Stokes Mortars and rifle grenades on machine- gun nests was very great.

Where these mortars were put into action they served boldly and with good result.

There were some instances reported of Doughboys using mortar shells by removing the safety pin and then throwing them in the manner of large hand grenades. Due to the power of the 3" mortar shell as compared to a hand grenade, this practice, while effective at times, was fraught with danger. An interesting example of this method of using Stokes mortar shells was related in a dispatch from the 51st Infantry Brigade of the 26th Division:

One of the most effective uses of trench mortar shells was to carry a couple of them with time-fuses attached and drop them down the vent shaft, or chimney, or throw them down the stairway of a Heine dugout. There would be a dull thud and then silence. .

The only recurring negative aspect of the trench mortars was the difficulty experienced at times with maintaining sufficient supplies of mortar rounds. This is mentioned in a dispatch from the 102nd Infantry Regiment of the 26th Division:

.Like the hand-grenade each of these weapons (Stokes mortars) offered a problem in transportation and ammunition supply...

Preparing for Action

However, problems with the supply of ammunition does not seem to have negatively affected the performance of the Stokes mortar during the war. A few French-made 58mm mortars were also reportedly acquired by the AEF, but these were very few in number and saw extremely limited use as compared to the 3" Stokes mortar.

By the time of the Armistice, the 3" Stokes trench mortar was an integral part of the armament of the AEF. After the war, the weapon remained a standard item of issue. Most of the 3" Stokes mortars in the military's inventory were subsequently modified by the addition of improved bipods and sighting apparatus. The 3" mortar was supplanted prior to WWII by the 81mm mortar although some of the modified First World War vintage mortars remained in use through 1945.

Excerpted from U.S. Infantry Weapons of the First World War.
Reprinted by permission of Bruce N. Canfield. Bruce is an internationally recognized authority on Post - Civil War American weaponry. Photos courtesy of the Author, Konrad F. Schreier, Jr. and Ray Mentzer. Visit Bruce's website at www.brucecanfield.com to contact him or to order any of his works.

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