The 13-Inch Trench Mortar fired a spherical shot made up of cast-iron 1½ inches (38mm) thick and filled with up to 12Lbs (5.5Kg) of gunpowder which was set of by a simple timing fuse. The complete shell weighed some 200Lbs (91Kg). The timing fuse allowed the mortar be used as an air-burst or ground-burst weapon as required. The Mortar had a range of up to 2 miles (3,250 metres).
The mortar would send a shot high in to the air to fall steeply beyond castle walls and other fortifications directly on to the target. This type for fire, where the target can not be seen is called indirect fire.
The spigots protruding from the base of the Mortar shown on the left were used the transport the base on lengths of timber. The handles on the barrel were used to mount and dismount it from the base.