Virtual
War Memorial
Australia

Unit designation of artillery units in the AIF was confusing; none more so than the Mortar Batteries.  The Mediums and Heavies were formed into batteries of four (heavy) and six (medium) mortars attached to each division.   They were initially designated "V,X,Y,Z/n” where ‘n’ was the Division Number. From February 1918 they were reorganised and moved from Divisional to Corps Troops.  The following is a listing of the 1st Division Medium and Heavy Mortar Batteries:

V1A Heavy Trench Mortar Battery 17 April 1916 to 21 February 1918

X1A Medium Trench Mortar Battery 17 April 1916 to 21 February 1918
Y1A Medium Trench Mortar Battery 17 April 1916 to 21 February 1918
Z1A Medium Trench Mortar Battery 17 April 1916 to 21 February 1918
1st Medium Trench Mortar Battery 21 February 1918 to beyond November 1918
2nd Medium Trench Mortar Battery 21 February 1918 to beyond November 1918

Mortars are simple but terrifyingly effective weapons; almost as old as gunpowder itself.  They are relatively short barrelled, most often smooth bore weapons that fire projectiles at a high angle at relatively modest velocities.  This makes for modest pressures and therefore relatively simple manufacture.  The bombs are generally but not always, fin stabilised, with a point detonating fuse.

At the start of the First World War, the Trench Mortar did not exist in the British Army.  The Germans had them, where they were known as Minenwerfers, but certainly not in great numbers. They were still few in number in 1914/15.  Very few were available at Gallipoli, where they and howitzers were highly valued in order to overcome 'terrain masking' whereby intervening terrain features impeded flatter trajectory field and naval guns;  mortars and howitzers with their high angle fire  (greater than 45 degrees) can reach over and behind intervening ridges and hills with deadly effect.

The mortar’s characteristic high angle trajectory suited it to trench warfare.  Its capacity to lob bombs right into trenches soon ensured that demand for them grew.  The suffered one major drawback;  their relatively short range meant they were necessarily located close to the front lines, which did not enamour them to the infantry (because they attracted enemy artillery fire) and made them vulnerable to direct infantry assault.

On the Western Front, weight of shell was imperative for overcoming enemy defensive positions, so medium and heavy artillery of all kinds became crucially important.

There were four key mortar types.

• The light trench mortar was the Stokes 3 inch mortar.  It was effectively not much more than a simple tube for a barrel, with a bipod to support it and a steel base plate on which to mount the tube and bear its recoil.  It fired a finned 80mm diameter bomb to about 1000 yards, its range being improved throughout the war.  These were issued to Light Trench Mortar Batteries, attached to each Brigade Headquarters.  They were relatively mobile and could be dismantled and packed up in minutes.  The Light Trench Mortar Batteries are separately described.

• The second category were  the medium mortars, of which there were two main types.  The first was the 2 inch Medium Trench Mortar which fired an overbore bomb.  Overbore means the bomb was greater in diameter than the barrel.  It was fitted into the barrel by means of a cylindrical spigot or rod.  The bomb was described as a ‘toffee apple’ or ‘plum pudding’ bomb, weighing 23kg.  It was a relatively short barrelled weapon and had a heavy elevation and traversing gear mounted directly to the baseplate.  They were notoriously prone to ‘drop-shorts’ (which coincidentally is a derogatory term for gunners).  An interesting characteristic of these mortars is that they could be fitted with a captive piston projector which served as a silencer  / suppressor.  These however slowed the rate of fire.

• The 6 inch Newton Medium Trench Mortar which replaced the 2 inch weapon, was a rather bigger device.  Like the Stokes, its barrel was a steel smooth bore tube.  It also had a massive baseplate, but rather than having a bipod, it was supported by three steel wire rope guys that attached the barrel to the baseplate;  two effected traversing and one for elevation.  These made ‘laying’ or aiming the mortar much more complex.  The bomb weighed 21 kg with a range of 1,300m.

• And then there was “The Flying Pig”.  The 9.45 inch Heavy Trench Mortar was a beast.  Derived from a French design (also used by the Americans) it fired a massive fined projectile of 69kg about 2,400m.  The projectile could be seen flying through the air, hence the nickname.  It was ideally suited to pulverizing strong points, pill boxes and dugouts, and was capable of blowing a crater 3.5m deep and 8m wide.

As the Battle of the Somme ended in November 1916, the British and Empire Armies started rebuilding for the campaigns of 1917. Improved propellants for the 3 and 4-inch Stokes and a new medium mortar were introduced. In the autumn of 1916 a Major Newton developed the use of extra charge rings that slipped over the rear of the bombs that enabled the range of the 3-inch Stokes mortar to be extended to 677 metres. Further improvements in the charge rings saw the range extend to 754 metres and by the beginning of 1918 the 3-inch Stokes to 1,143 metres. This was the maximum range that could be obtained using the cylindrical bomb due to its poor drag coefficient and the mortar barrel having a maximum chamber pressure of two tons per square inch.

Major Newton had also developed a new medium mortar that used the same firing system as the Stokes mortar. This became the 6-inch Trench Howitzer Mark I, commonly known as the ‘Newton’ or ‘Stokes-Newton’. The design was successful with 1,700 being ordered in late January 1917. Deliveries began in May, and in June the ammunition started arriving in France. In 1917 1,929 Newton mortars were produced with a further 609 in 1918 with ammunition production 239,471 and 1,134,805 rounds respectively. 

The 6-inch mortars replaced the 2-inch medium mortars as soon as they arrived however they had not completely replaced the 2-inch mortars by the beginning of 1918. The mortar weighed 189 kilograms in action in action and fired both 35 kilogram steel and 25 kilogram iron bombs. Both bombs contained 10 kilograms of high explosive. The steel bomb had a minimum range of 460metres and a maximum range of 950 metres and the iron bomb had a minimum range of 90 metres and a maximum range of 1278 metres with a maximum effective range due to dispersion of 1,000 metres.

Steve Larkins  July 2014

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