The 3-motion breech was replaced by a single-motion interrupted screw breech which had an axial T vent running through it into the chamber, designed to take a T friction tube.
The new firing mechanism involved a new TFrictionPushTubeMkIBLC15pounder.jpg which was inserted into the axial breech vent. The crosspiece of the T was positioned pointing upwards. A long layer's guard was added to the left side of the cradle projecting behind the breech. A spring-loaded firing handle was built into the layer's guard. When cocked by pulling back and then released, it sprang forward and struck a firing lever on the breech, which translated the forward motion to a downward motion and propelled a firing plunger into the T of the friction tube which in turn ignited the cordite propellant charge.
10th Battery of the Royal Canadian Field Artillery (RCFA), equipped with 4 guns, fought a notable action in the evening of 22 April 1915 north of St Julien to hold the left of the British line where the German infantry was breaking through following their gas attack on the first day of the Second Battle of Ypres. Hence when skillfully utilised in the role it was intended for - against troops in the open - the gun was still effective despite being obsolete. Where infantry avoided being caught in the open the guns were of limited use due to their light shell.
Number 1 15 Pounder Camel Battery RGA (today's 21 (Air Assault) Battery) served with 6 guns with the Indian Expeditionary Force in the Aden hinterland from 1915 -1918, to defend the important port at Aden against any Turkish advance. In July 1915 actions were fought in initially losing and then regaining the British advanced post at Sheik Othman controlling the water supply to Aden. Sgt Curtis was awarded the Distinguished Conduct Medal for saving his gun in these actions (presumably the first, in which 2 guns were lost). The Camel Battery was present when the British captured Hatum in January 1918.