A mortar is a muzzle-loading type of weapon firing bombs indirectly at its target, at low velocities, comparatively short ranges (to other types of artillery), and high, arcing trajectories. A modern mortar has a fixed firing pin in its base, with a propellant charge attached to the bomb.
Mortars predate the 20th Century, though earlier types tended to be heavy and mostly immobile weapons used in siege warfare. Mortars became particularly useful in the trench warfare conditions of the First World War. By the time of the Second World War, a variety of mortar types were in use, with light mortars being man-portable and operable by a single person, and able to fire a variety of munitions including High Explosive, smoke and illumination rounds. Medium sized mortars were common in the major militaries of the world, firing rounds generally 81-82mm in diameter. Heavier mortars such as the 4.2-inch Mortar or German 10cm Mortar were also used at the formation level.
The advantages of mortars are that they can be fired while in complete cover (i.e. not exposed to direct fire from the enemy), and by 1939 even the "medium" mortars were were light enough to be man portable.
By 1914, experiences in previous conflicts such as the Russo-Sino War of 1904-05 had demonstrated the effectiveness of small explosive devices such as the hand grenade and the mortar. The Germans began to stockpile mortars, with 150 on hand in Aug 1914. The French and British had not developed the concept of the mortar before the war, and even through the first year of the First World War little attention was paid to mortars.
German mortars in 1914 - referred to as minenwerfer (German: mine thrower, literally) - had been a recent development, fired a 25cm bomb from a rifled tube, and weighed about 95kg each (and consequently were mounted on wheeled carriages. Lighter mortars of 17cm and 7.6cm were also on inventory, and mass production commenced after the outbreak of war.
It was not until Oct 1914 that the commander of the British forces in France requested "some special form of artillery" capable to deal with trenches at close range, and it was not until Dec 1914 that an "official" trench mortar made its way to the Continent, where it was declared unsuitable.1
It was not until late 1915 that British production of mortars was stepped up, and the standard design at the time had no rifling or even sights. These weapons had a maximum range of 1,500 yards and a time fuze of 25 seconds, later chanted to a percussion (impact) fuze.
British mortar developments did catch up to those of the Germans and Mister F.W.C. Stokes - later Sir Wilfred Stokes, KBE - developed a simple but effective weapon in Jan 1915. The Stokes Mortar inspired most modern mortars that followed it. The design included a smooth metal tube with a base plate to absorb recoil (the early British mortar had no means of doing this) and a light bipod. The weapon fired from a fixed firing pin at the base of the tube.
The ultimate version of the Stokes mortar fired a 3-inch diameter bomb of about 4.5kg, with a modified hand grenade fuze. Rate of fire was as high as 22 bombs per minute with a maximum range of 1,200 yards. Other mortars included a light (2-inch) mortar and a heavy mortar of 9.45-inches to complement the medium 3-inch.
By the end of 1915, each British division had 24 light Stokes mortars (of 2-inch size, replaced in 1917 by the 3-inch Stokes), 12 mediums, and a variety of heavy mortars. The term Trench Mortar was widely used in this period to refer to mortars and the units into which they were grouped, as was the term "Toc Emma", the phonetic abbreviation for "TM".
Mortars were especially useful for use against enemy trenches due to the high angle of their trajectory, allowing bombs to drop directly into enemy positions. Larger mortars were sometimes employed to cut enemy wire.
The French adopted the Stokes design once it had proven its worth, and the two nations worked on improving range and accuracy throughout the war.
At least one source mentions that the Canadians (namely Major A.G.L. McNaughton) invented a 91kg mortar bomb, 9.45-inch in diameter, which became nicknamed the 'blind pig'.
Modern mortars generally consist of three components: a barrel (also called a tube), a base plate, and in most cases a bipod, though light mortars could be operated effectively without the latter.
Ammunition for mortars have developed into both fin-stabilized and spin-stabilized varieties, the latter requiring a rifled barrel (and a consequently higher loading time).
First World War
Canada had no mortars in 1914; by 1918 the Canadians had adopted light (3-inch Stokes Gun), medium (6-inch Newton Mortar) and heavy (9.45-inch Newton Mortar) weapons. The most commonly used were the light mortars, batteries of which were added to the establishment of infantry battalions and brigades. A Trench Mortar Battery consisted of eight mortars, usually, organized into four sections.
The light Trench Mortar Battery had several advantages over artillery common to mortars as described above in the introduction. The 3-inch Stokes Gun was particularly useful for being so light, but range was only 700 yards and the battery did not have an ammunition column attached, meaning carrying parties had to be provided from infantry units to keep ammunition in the front lines.
Second World War
During the Second World War, each Infantry Platoon was equipped with a 2-inch Mortar. Each Infantry Battalion also had a Mortar Platoon equipped with the 3-inch Mortar. Each Machine Gun Battalion had a 4.2-inch Mortar company added to it after the beginning of the war.
After the 1945, as part of NATO's standardization of weaponry, Canada adopted the M19 60mm Mortar, a US design issued during the Second World War.
In 1967, Canada received the first C3 81mm Mortars for its mechanized infantry battalions.