mortars

mortars. A mortar is defined as a weapon which fires only at angles above 45 degrees, and, so far as the Second World War is concerned, is usually interpreted as meaning the light smooth-bore weapons employed by infantry for their own close support. The term is, however, also correctly applied to heavy rifled ordnance of the howitzer class used for coastal defence by some nations, though few ever saw use in 1939–45.

Infantry mortars were largely derived from two prototypes, the British Stokes mortar and the French Brandt mortar, both of which were developed during the First World War. In the 1920s both, but more especially the Brandt, were copied and licensed for manufacture in several countries, so that most of the world's mortars were very similar weapons in similar calibres. They fell into three groups: the light class were of 50–60 mm. (1.95–2.3 in.) calibre, the medium of 81–82 mm. (3.15–3.2 in.) calibre, and the heavy of 100 mm. (3.9 in.) calibre and above. They were almost all of similar construction; a smooth-bore barrel, the end of which rested upon a steel baseplate which spread the recoil shock to the ground and a supporting bipod or tripod which held the barrel at the desired elevation and was provided with adjustments to permit elevating and traversing the barrel.

Mortars: Mortar bomb lethal radii. Based upon standard 1939–45 period HE bombs. Based upon 70° angle of descent, average meadowland.

These figures can be considered the ‘worst case’; the actual distribution of splinters resembles a figure eight with the bomb in the centre and the two loops at each side. Very little goes forward or backward, the greatest area of risk being at the side, and that is what these figures represent. The lethal area immediately in front of the bomb is a matter of 4–5 m (13–16 ft) at the most.
Source: Contributor.
50 mm/2 in	6 m (19.7 ft)
60 mm	10.5 m (34.5 ft)
80–82 mm/3 in	15 m (49 ft)
107 mm/4.2 in	15 m (49 ft)
120 mm	20 m (65.5 ft)

The projectile, generally called a ‘bomb’, was usually of tear-drop shape with fins at the tail. The propelling charge was in two parts; the ‘primary’ charge was a shotgun cartridge in the centre of the tail with a filling of smokeless powder, and the ‘secondary’ charges were fixed around or between the tail fins in cloth bags or celluloid containers, retained by clips or springs. To load, the bomb was simply dropped down the barrel so that the primary cartridge struck a fixed firing pin. This exploded the primary, which ignited the secondary charge and blew the bomb from the barrel. Some mortars had firing pins which were actuated by triggers.

The US Army was unusual in having a rifled mortar; this demanded a somewhat more complicated bomb in order to allow drop-loading but still take the rifling when fired, but it was of superior accuracy and fired a heavy 107 mm. (4.2 in.) bomb. The German Army used an 81 mm. mortar as their standard until they encountered a much superior 120 mm. (4.7 in.) design used by the Soviets; after putting captured 120 mm. mortars into service they began manufacturing a copy and this generally replaced the 81 mm. as their standard.

The Soviets also used much heavier mortars than any other country, having 160 mm. (6.25 in.) and 240 mm. (9.4 in.) weapons manned by artillery. These were of special design, in which the 160 mm. allowed the barrel to be tipped down to permit muzzle loading and the 240 mm. also tipped the barrel forward but was breech-loaded. Although cumbersome, they were quicker and cheaper to manufacture than conventional artillery pieces.

The British Army used 2 in. (51 mm.), 3 in. (76 mm.) and 4.2 in. (107 mm.) weapons, the latter being operated by artillery regiments in the Burma jungles where the conventional field artillery was not well suited to the terrain. The Japanese used several mortars, largely based on Brandt designs. The celebrated ‘knee mortar’ was so-called because it could be carried strapped to a man's leg. That it was fired off the bent knee was a myth.

Italy and the USA used licensed versions of the French 60 mm. and 81 mm. Brandt mortars. Since the German 81 mm. was also generally of the Brandt pattern, and since the bombs of all these mortars were similar, it meant that American, Italian, and German bombs could be used in each others' weapons, a fact put to use in the Italian campaign.

Mortars were heartily disliked by the infantry, since they were quick to come into action and deadly in their effect. Towards the end of the war the British Army had some success in adapting surplus air defence radar sets to detect a mortar bomb in flight. The trajectory could then be plotted and extrapolated backwards so that its position could be located. This technique was considerably improved upon in post-war years.

Ian Hogg