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.