A mortar is an indirect fire weapon that fires explosive projectiles known as (mortar) bombs at low velocities, short ranges and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber.
A mortar is relatively simple and easy to operate. A modern mortar consists of a tube into which assistant gunners drop a purpose-designed bomb. The tube is generally set at between 45 and 85 degrees angle to the ground, with the higher angle giving shorter firing distances. The bomb has a small baseline charge and no cartridge case; for extra range propellant rings are attached to the bomb's fins. When it reaches the base of the tube it hits a fixed firing pin, which detonates the baseline charge and fires the projectile. Some mortars have a moving firing pin, operated by a lanyard; others may be fired by a trigger.
These attributes contrast with the mortar's larger siblings, howitzers and field guns, that fire shells at higher velocities, longer ranges, flatter arcs, sometimes using direct fire. These weapons are also breech-loaded, while most mortars are muzzle-loaded.