Stokes Mortar (3-inch)
81mm Light Infantry Mortar / Trench Mortar
Portability is what made the Stokes Mortar such an important weapon during World War 1.
Authored By: Staff Writer | Last Edited:
While mortars largely fell out of interest prior to World War 1, the stalemate of trench warfare forced national armies to revisit its battlefield value. Mortars had been in use for centuries prior and were "indirect fire" weapons capable of engaging enemy forces not only at distance but also without line of sight. As such, entrenched enemy troops were no longer safe from incoming artillery for mortars could dislodge concentrations and also held a heavy psychological effect to boot. The larger counterpart to the mortar was the field howitzer which was doubly effective in the same role though these designed were generally large, heavy, cumbersome beasts when compared to the portability inherent in light mortar designs. The British Stokes Mortar (3-inch) was one of the most famous of the early modern light mortars. It was drawn up by English engineer Sir Wilfred Stokes (hence its designation) who eventually took a post within the "Inventions Branch of the Ministry of Munitions" during World War 1.
Tensions had officially culminated with the outbreak of world war in the summer of 1914 to which Britain declared war on the German Empire after the Empire had sought to invade France through British ally Belgium. Trench warfare bogged the Western Front within months of the declaration as both sides dug in for the long war ahead (initially, all sides thought the war would be over by Christmas and the conflict was greeted with euphoria by large crowds before the fighting started). With the stalemate an ever-growing problem to warplanners and politicians alike, various methods of removing the enemy were considered - among these being poison gas, flamethrowers, portable machine guns, the aircraft, the tank (then known as "Landships") and - of course - artillery.
Design of a new modern portable light field mortar for British troops began in early 1915. Comparatively, the German Army was making good with their own light mortar at the time, this the 7.58cm leichter Minenwerfer series. To match the enemy advantage "pound-for-pound", the British Army required an indirect weapon of similar scope that could be managed with relative ease in battle and moved into position at a moment's notice (in the latter case, for the taking and securing of an enemy trench for example). The Stokes 3-inch design was presented to British authorities in June of 1915 but interest was low for the new weapon was not cleared to fire existing ammunition supplies. However, with some internal help, the Stokes design came to fruition and the mortar was eventually adopted by the British Army during the war. From then on, the type went on to see extensive combat service through the whole of the conflict - giving a good account of itself in battle. It began wide scale operational service in 1916 and revisions greeted the design throughout the war.
A typical Stokes Mortar crew was two personnel - one to manage the elevation controls and the other to handle the ammunition. The entire system weighed in at 108lbs (despite its weight it was still a "light" mortar classification) and fired a 10lb 76.2mm high-explosive (amatol filled) cylindrical projectile out to 800 yards though effective range was closer to 750 yards. The smoothbore launch tube held an elevation limit of 45- to 75-degrees. Overall, the Stokes mortar system was very conventional even by modern standards, the design comprising a baseplate, launch tube, elevation controls, bipod and the projectile. For transporting, the Stokes design broke down into three primary components - the barrel, baseplate and bipod (not taking ammunition supply into account). A trained crew could fire between 22 to 25 rounds per minute if required but generally held to a 6-8 round per minute limit for when in the general sustained fire role (lest the barrel overheat).
In practice, the Stokes mortar was traditional in its overall operation. Once sighted against the proper target area (mortars were "area effect" weapons, not "direct target"), the ammunition handler would drop the 3-inch shell down the awaiting open muzzle of the launch tube. The projectile then struck a firing pin at the bottom of the tube which actuated an impact sensitive primer on the shell, thusly detonating the propellant of the shell with the resulting force sending the projectile out of the muzzle of the tube at speed. In this fashion, the Stokes mortar could offer repeating, indirect fire as needed in support of friendly actions - usually preceding an infantry charge by helping to "soften" enemy targets or provide suppression. Each 3-inch projectile could be further "ranged" by the addition of propellant "rings" of which up to four such rings could be affixed to a projectile's base. The projectile itself held a basic charge that allowed for a standard range to be reached though this also varied as related to the launch tube's elevation angle (the higher the angle, the shorter the range). Each propellant ring added as much as 100 yards of range to a Stokes Mortar holding a 45-degree elevation.
After the war, a new fin-stabilized projectile was finally developed which gave greater accuracy while an improved charge gave it greater range. The Stokes 3-inch mortar was such a success that it remained in the British inventory until 1936 before being replaced by the "Ordnance ML 3-inch Mortar" series prior to World War 2. Other operators of the Stokes design included the United States, Greece, Poland and Portugal. British Commonwealth forces also made use of the type during World War 1 and beyond. The basic 3-inch Stokes design eventually influenced a 4-inch (101mm) and 6-inch (152mm) Stokes design and these fired larger, more powerful projectiles including those containing incendiary, smoke and poisons.
The Stokes 3-inch mortar was certainly one of the engineering success stories of the First World War in terms of its military value.