Designed by Sir Wilfred Scott-Stokes (he was knighted for this work), the managing director of a mechanical engineering firm, Ransome & Rapier of Ipswich, the Stokes trench mortar was designed to answer the need for a mobile and quick firing trench mortar and Scott-Stokes had a prototype ready for testing by December 1914. Though highly thought of by the Army the mortar did not immediately go into production as it was still beleived the war would be relatively short-lived. Within a few months opinions had changed and the 3-inch Stokes Trench Mortar, Mark I went into production in the Spring of 1915. It can truly be said that the design was the forerunner of all mortar designs since.

The gun was simplicity itself. A 51 in. long, 3 in. diameter barrel was supported by a bipod and sat on a base plate. The Stokes was fired by dropping an 11lb shell down the tube onto a firing pin at the base of the tube. This set off a shotgun-like blank cartridge and this in turn ignited propellant rings attached to the mortar shell. The angle of the bipod could be adjusted to increase or decrease the range and the shell could be fired to a maximum range of 800 yards. The safe minimum distance was 100 yards.

The Stokes came in three parts: the firing tube (43 lbs), the base plate (28 ibs) and the bipod (37 obs), a total of 108 lbs and at Gommecourt several guns were taken across to support the attack of the 169th Brigade.