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In the years immediately following the end of World War 1 the mortar tended to go out of fashion. For the close support of infantry most armies favoured the 'infantry gun', which in the British Army was to be the QF 3.7-inch howitzer.

However, to provide a greater range and more effective projectile than the current grenade launchers or rifle grenades, there appeared during the 1920s and early 1930s a number of small mortars. The simplest of these was the British 2-inch (50.8-mm). A Mark 8 version with a 14-in (36-cm) barrel was produced for Airborne Troops.

2-inch Mortar

The original 2-inch mortar featured a large base plate and collimating sights with elevation and cross-level bubbles but experience soon brought modifications. Subsequent marks carried much smaller base plates and dispensed with sights. Laying was by eye and judgement, the sole aid being a white line painted on the barrel. The shortness of the barrel precluded the use of the Stokes principle for firing so a small trigger (or trip) mechanism was provided at the breech. The standard projectile was a HE bomb with an impact fuze in the nose and a four-finned tail unit with a single primary cartridge.

After World War 2 most light mortars fell into disuse but the 2-inch mortar was retained in Commonwealth forces to provide smoke and illumination. During World War 2 a bomb with a barbed head like a harpoon and trailing a long thin wire was made to be fired across a minefield, then dragged back to catch on any trip-wires present.

Figure 24: How the 2-in mortar was manned in action.

5-cm Mortar

Few other nations adopted 5-cm mortars; notable exceptions were Germany, Italy, Japan and the Soviet Union. Performances were comparable with the British 2-inch but all were heavier and were mounted on bipods as orthodox types of greater calibre. By the end of the war they had largely ceased to be employed.

German 5-cm Granatwerfer Mortar 1936: Length:   19.3 inches (46 cm) Weight:   30.9 lbs (14 kg) Firing mechanism:   Trip Elevation:   42-90° Projectile weight   HE:  1 lb 15½ oz (895 g) Range:   547 yards (500 m) Rate of fire:   4 rpm

An interesting example of a foreign 5-cm mortar was the German 'granatwerfer' (literally 'grenade-thrower') Model 1936. Tests on a captured specimen carried out in Britain in 1941 prompted the report that it was 'well-constructed and easy to operate but the degree of accuracy is unnecessarily high!' Surely this must be the first time any weapon was ever classed as too accurate!

Figure 25: German 5-cm Granatwerfer Model 1936

6-cm Mortar

Other nations, including China, France, Spain, and the United States, adopted 6-cm mortars based on a French design. The 6-cm mortar was a much heavier equipment than the 5-cm, with a maximum range of 1640 yards (1500 m). Not only was the 6-cm too heavy for platoon use, but the maximum range was too great for a platoon's needs. They all looked pretty much alike (typical example in Figure 26). Most other nations' 6-cm mortars are based on the same design. The 6-cm mortar indicated is still in service with French and German forces.

French Hotchkiss-Brandt 6-cm Mortar: Length of barrel:   28.5 inches (72.4 cm) Weight:   33 lbs (14.8 kg) Range:   2187 yards (2000 m) Rate of fire:   25 rpm Sight:   Cross-levelling collimator Ammuntion:   HE, SMK, ILL Detachment:   3

Figure 26: French Hotchkiss-Brandt 6-cm mortar.

3-inch Mortar

The 'infantry guns', eg the QF 3.7 howitzer mentioned above, intended for the close support of infantry after World War 1, were expensive and difficult to manufacture. Thus, during the depression years of the 1920s and 1930s, nations began to seek cheaper alternatives. In 1932 the British Army decided to replace the 3.7 howitzer with the 3-inch (76.2-mm) mortar as the standard infantry support weapon. It remained in use by Commonwealth armies throughout World War 2.

After 1918 the 3-inch mortar based on the original Stokes principle was developed as the 'Ordnance ML 3-in mortar Mark 1' with a range of 1600 yards (1463 m). Improvements, including a heavier barrel and base plate, permitting an increase in propellant charge, resulted by 1939 in the Mark 2, with a range of 2750 yards (2525 m). However, contemporary German and Italian mortars performed more effectively both in range and in lethality of projectile.

Still more attempts to improve performance resulting in a Mark 4 did not come up to expectations so in 1945 efforts were directed towards replacing it with an 81-mm (3.2-in) model.

Ordnance 3-inch ML Mortar Mark 2: Calibre:   3-inch (76.2-mm) Length of barrel:   46.85 inches (119 cm) Weight in action:   126 lbs (57.2 kg) Elevation:   45-80° Top traverse:   11° Minimum range:   125 yards (114 m) Maximum range:   2750 yards (2515 m) Bomb weight HE or SMK:   10 lbs (4.54 kg)

Figure 27: Ordnance 3-inch ML Mortar Mark 2

The most significant improvements over the Stokes included the provision of elevating and traversing gears and a sighting system, including a simple form of dial sight. Thus, the 3-in mortar could be employed in the indirect fire role in the same manner as a field gun. Although not matching the opposition it proved a useful and popular piece in action throughout World War 2.

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