4th Division Heavy and Medium Trench Mortar Batteries, AIF

Normal 9.5 inch flying pig at pozieres

About This Unit

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The 4th Division Medium and Heavy Trench Mortar Batteries were:

V4A Heavy Trench Mortar Battery August 1916 to 21 February 1918 (transferred to Corps Control)
X4A Medium Trench Mortar Battery August 1916 to 21 February 1918
Y4A Medium Trench Mortar Battery August 1916 to 21 February 1918
Z4A Medium Trench Mortar Battery August 1916 to 21 February 1918
7th Medium Trench Mortar Battery 21 February 1918 to beyond Armistice November 1918
8th Medium Trench Mortar Battery 21 February 1918 to beyond Armistice 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.  Trench Mortars were very few in number at Gallipoli, where they and howitzers were hiighly 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.

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

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.

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, although its range 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 silencer  / suppressor.  These however slowed the rate of fire.

The 6 inch Newton Medium Trench Mortar 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 and slower than the Stokes.  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.

They were formed into batteries of four mortars attached to each division (Medium mortars were organised in batteries of six.   They were designated "V/n” where ‘n’ was the Division Number. From February 1918 they were reorganised and moved from divisional to Corps Troops.

In action, a heavy timber platform was constructed so as to be embedded in the ground.  The mortar base mounting was immovably secured on this.  The mortar carriage sat on the base and could traverse.  The mortar barrel was mounted on the carriage which allowed elevation.

Steve Larkins  July 2014


 We would particularly like to encourage individual historians researchers or members of unit associations to contribute to the development of a more detailed history and photographs pertaining to this unit and its members.

Please contact  admin@vwma.org.au  (mailto:admin@vwma.org.au)for details on how to contribute.