1915: The Mortar Emerges As a Major Weapon

Stokes Mortar by John Nash

Tactically, by the end of 1914 it was clear that the magazine rifle, the machine gun, and quick firing (QF) artillery had made the battlefield lethal to an unprecedented degree. The only way to survive the storm of lead was to dig in, and as the advantage shifted from attack to defense, the opposing armies were soon mired in stalemate. The balance of importance shifted from the élan of the infantry to the skills of the military engineer, who was responsible for building and defeating fortifications and fieldworks and ensuring communications.

When defending or attacking fortifications, it was often difficult to use direct-fire weapons like rifles; instead it was useful to have short-range area weapons such as explosive grenades. Hand grenades, and short-range bomb-throwers such as the German Minenwerfer, formed part of the equipment of the engineers and pioneers, but at first they were available only in the relatively small quantities that had been anticipated as being sufficient for the occasional set-piece siege.

Hand grenades were useful in the assault and defense, and rifle-grenades could sometimes be projected as far as from one trench line to the other, but there was  a need for a more powerful weapon capable of indirect fire and light enough to be manhandled forward to give intimate support to an assaulting force. 

German Minenwerfer

The German Army had come into the war with the Minenwerfer but:

. . .These were only held in small quantities, and at first they remained the responsibility of the Pioniere. The Minnenwerfer batteries were distinct both from the infantry they were supporting, and the artillery, of whose fire-planning they should have been a part.  U.S. Army Document

The British, though, needed to improvise. In siegecraft the historic solution had been the 17th-century Coehorn mortar, a stubby barrel fixed at an angle to a substantial wooden base and firing a spherical iron shell with a gunpowder  filling. Its descendants had finally fallen out of use after the American Civil War, but in 1915 the French Army found some in the dusty recesses of its stores and was able to supply these antiques to the BEF (who called them "Toby mortars").

During the siege of Port Arthur (Aug 1904–Jan 1905), British observers had taken note of improvised Japanese "trench mortars." In 1915, when the need for "trench howitzers" became urgent, the Royal Engineers set about designing and manufacturing light mortars that could be rapidly supplied to the infantry. During that year, eight patterns of trench mortar would enter British service on the Western Front, in addition to cruder bomb-throwers powered by springs or rubber bands. 

French Mortar of the Early War

Unlike the sophisticated Minenwerfer in German service, the "Indian Pattern Trench Howitzer" designed by the 3rd (Bombay) Sappers & Miners consisted simply of a 24-inch-long, 3.5-inch-caliber seamless tube plugged at the lower end and fitted to a base plate or spade. A bipod fitted with a simple elevating screw mechanism was clamped to the barrel. Improvised "jam-tin" bombs were loaded from the muzzle, and a propellant charge was ignited by way of a touch hole near the base. 

The later excellent weapon designed by Wilfred Stokes that was first used at Loos in 1915 and went into general service in 1916 was quite similar to the Indian Pattern, but the propellant charge was contained in the tail of the bomb and ignited by a firing pin in the base of the barrel. It fired a 10 lb-11oz bomb out to 800 yards and could be carried by advancing infantry. 

The Indian Pattern and Stokes mortars gave the British infantry its own indirect-fire support weapons. During 1915 each BEF division gained three batteries of four trench mortars, which were subsequently reorganized as two batteries of six each. 

Meanwhile, the same challenges and problems that were leading all the combatants to develop something like the "trench howitzer" were causing all the staffs to expand and improve their field and heavy artillery. More on that in future postings on Roads to the Great War.

Source: Over the Top, August 2015