Ordnance ML 3-inch Mortar History

Among several of the unsung British war weapons to see action in World War 2 was the Ordnance, ML Mortar, 3-inch. The weapon served throughout the conflict and provided British Army and Commonwealth personnel with the capability to lob explosive projectiles against enemy emplacements and troop concentrations. Initial versions lacked the range of her wartime contemporaries but, as the war progressed, there was little that the mortar system could do, becoming the standardized British infantry mortar weapon until the 1960s.

During World War 1, the British Army relied on their trusted 3-inch Stokes Mortar system of 1917 and it proved a sound weapon well into the post-war years. The interwar years proved a rather slow time for weapons developed in the British military and some casual thought was given to upgrading general firepower at the infantry level. Initially, it was envisioned that a company would be stocked with light machine guns to bring copious amounts of directed firepower into the fold. While this design direction maintained some merit in concert with the popularity of automatic weapons, it would prove a costly venture to produce, not to mention the carrying of machine guns bogging down infantry forces. Instead, the Stokes Mortar design was revisited in the 1920s and evolved into a more modern fighting form. Its 81mm projectile was always a good fit for indirect fire / ranged combat and this was proven time and again in The Great War.

The basic Stokes design was modified into the "Ordnance, ML Mortar, 3-inch Mk II" and production made it possible to see it achieve the numbers required when war officially broke out in Europe to begin World War 2 in 1939. British Army personnel went into combat with the new Mk II model against the forces of the Axis, spearheaded by the well-trained and well-stocked German Army. The British weapon sported an operational weight of 112lb firing a 10lb projectile out to 1,600 yards with a 650 feet per second muzzle velocity and required at least three specially trained personnel in its use.

After some operational experience, a severe design shortcoming came into play, particularly when the Mk II was compared to the German infantry mortar systems (namely the GrW 34 series). The Mk II was simply out-ranged and required British troops to be in very dangerous proximity to the enemy for the system to be able to have any sort of tactical effect on a given battle. German mortars ranged out to 2,600 yards while the British Mk II model could reach just 1,600 yards in ideal conditions - a 60% difference in comparison. British engineers, therefore, went back to work on improving the Mk II design.

A period of reworking and testing followed by intense evaluations produced a new 3-inch mortar form with a lengthened barrel, new projectile with increased charge and inherently longer operational ranges (up to 2,800 yards). Within time, production supplied the demand and British troops now fought on equal footing with their Axis counterparts. For the interim, British infantry and Commonwealth Forces were relegated into using captured German or Italian mortars as well as their applicable ammunition stores while the Mk II was being reworked.

As the war progressed, the British 3-inch Mortar was further addressed to include a new sighting system as well as a revised baseplate. A more portable form was also developed to be used by paratroop elements and some were dedicated for use in the tropic and mountainous environments in the Far East where the British Army and Commonwealth Forces tangled with elements of the Japanese Empire. In the end, the British 3-inch Mortar proved a reliable and robust weapon system, cleared of all limitations seen in the initial production model and revised for the better. Crews soon learned the strengths of their 3-inch mortars and could even finagle a minimum range of 125 yards if required while playing with elevation and propellant charges to fine tune the mix. This short range performance could prove ideal in close-support actions against advancing enemy troops.

Design-wise, the Ordnance ML Mortar 3-inch was of a basic arrangement and conventional in function. The design was characterized by its major components - namely the launch tube, baseplate, bipod, sighting equipment and ammunition. The system was 81mm (3. 2") in precise caliber (despite the 3" used in the official designation)) and cleared to fire a standard High-Explosive (HE) projectile as well as smoke and illumination rounds. The mortar measured in at 1. 295 meters long while the barrel made up 1. 19 meters in length. When made ready to fire, the system weighed in at 126 lb while, when broken down for transport, the weapon required at least three personnel - each charged with transporting one of the major pieces into combat. The weapon's elevation as limited from +45 to +80 degree angles of fire and traverse was 11-degrees in either direction. Elevation and traverse controls were mounted on the bipod assembly while the sighting device was identified along the barrel, towards the muzzle end. The 81mm projectile weighed in at 10 lb apiece.

Operation was conventional with personnel sighting the weapon against the intended target area. One member then dropped the ready-to-fire projectile in through the muzzle to which the projectile fell down the launch tube and struck a firing pin at the baseplate, igniting the internal charge propellant. This explosion forced the projectile out of the tube and along a rudimentary flight path. Crews could then revise the traverse and elevation based on where the previous round fell and repeat the process all over again. The heavy baseplate served to retard the inherently violent recoil of such a weapon while also serving as a third support leg in conjunction with the bipod assembly. As an "indirect fire" weapon, the object of the mortar was to target areas as opposed to individual enemy forces. Its High-Explosive projectiles were very useful against concentrations of enemy personnel. Smoke rounds could be used to shield friendly tactical movements while illumination rounds were used in low-light settings to mark enemy positions.

Typically, the 3-inch mortar system was carried into position by mortar team personnel but it was not uncommon for the British Army to make use of their nimble little "Universal Carrier" tracked vehicles (detailed elsewhere on this site) in transporting the weapon at speed (note that the 3-inch mortar was not designed to be fired from the vehicle itself and had to be unloaded and setup to fire on the ground). This speedy transport allowed mortar teams the capability to reach a given area quickly, complete with ammunition supply in tow, and disembark to setup the mortar and make it ready to fire. A crew could also dig out the surrounding land and create a ground depression from which to fire from, providing the crew with basic protection from enemy return fire. So long as the ammunition supply was forthcoming, the mortar team could supply a steady rate-of-fire over the heads of friendly troops. The 3-inch design could also be dropped into action via parachute within hardened containers in three main sections - the barrel and bipod, the baseplate and an initial ammunition supply. Paratrooper elements need only recover the various parts, assemble the weapon and begin firing on enemies.

The Ordnance 3-inch mortar went on to serve beyond the United Kingdom, seeing service within the inventories of Australia, Canada, India, Ireland, Luxembourg, New Zealand and the Philippines. In the Philippines, the 3-inch mortar saw combat actions with counter-Japanese insurgency forces during its occupation during World War 2 and served into the 1960s. The wartime 3-inch mortar was inevitably replaced by the modern UK/Canadian joint design effort L16A1 81mm mortar beginning in 1965.

Ordnance ML 3-inch Mortar Specification


- In-Direct Fire / Siege / Area Effect


Overall Length:

1 mm (0. 04 in)

Barrel Length:

1 mm (0. 04 in)

Weight (Unloaded):

126. 10 lb (57. 20 kg)


Integrated Optics.



Manually-Fed; Pin-Actuated

Muzzle Velocity:

650 feet-per-second (198 meters-per-second)


12 rounds-per-minute

Effective Range:

8,250 ft (2,515 m; 2,750 yd)


Mk I - Original mark of 1917

Mk II - Base Series Designation

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