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After 1945 armies began to reappraise the mortar in the light of its wartime performance. One of the best to emerge was the Soviet 120-mm (4.7-inch), of which the Germans captured large numbers. So impressed were they that they copied it as their Granatenwerfer 1942, a very successful equipment. Firing a 34-lb (15-kg) bomb to 6000 metres (6560 yards), it was as effective as light artillery - especially when on a wheeled mount. As mortars were comparatively cheap to produce, and artillery equipments becoming more expensive, this mortar did much to set the post-war fashion.
First to receive attention by developers was the shell or bomb, which after all is the weapon of athe artillery, the gun or mortar simply being the means of putting it on the target. Early high explosive (HE) mortar bombs were of rough cast iron, without any machining of the outer surface. As they had to be loaded quickly and easily by dropping them down the barrel, tolerances in diameter were rather genereous, with significant loss of propellant gas pressure. Thus compared with a gun of like calibre the mortar was comparatively inefficient.
Machining the bomb over its whole surface corrected irregularities found in the old cast iron types, reduced skin friction with the air, and enabled windage to be reduced. The fitting of a plastic gas check which expanded on firing prevented the escape of propellant gas over the projectile. The changes improved both range and accuracy.
To obtain effective fragmentation with a cast iron bomb, an explosive filling of comparatively low yield, eg amatol, had to be used, thus limiting the lethal range and striking power of the fragments. To employ a more violent explosive such as TNT (tri-nitro-toluene, also known as tri-nitro-toluol) would simply blow the bomb to dust, producing blast effect only. This might give the enemy a headache but would not kill or wound him.
Many HE mortar bombs are now made with steel similar to that of which HE artillery shells are made, designed to handle explosive fillings of the same power as TNT. Thus their fragmentation effect will be greatly enhanced.
Let us look at a World War 2 example of a very efficient HE projectile. A 25-pr shell filled with TNT upon being detonated broke up into over 500 fragments each of which could kill or seriously wound a man. For planning purposes its lethal area was taken to have a radius of 35 yards (32 m) from the point of burst, but many casualties occurred beyond it. Indeed the 25-pr shell was claimed to have been 1.5 times as lethal as the American M1 105-mm shell as now fired from our light gun.
Modern ammunition described above does not come cheaply. Thus while the cost of manufacture of mortars remains reasonable the cost of their bombs is increasing.
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Wally Ruffell
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