Field gun
[Image:105L Schneider - model 1913 pic2.JPG |thumb|A post-WWI French 105 mm field gun]
A field gun is a field artillery piece. Originally the term referred to smaller guns that could accompany a field army on the march, that when in combat could be moved about the battlefield in response to changing circumstances, as opposed to guns installed in a fort, or to siege cannons and mortars which are too large to be moved quickly, and would be used only in a prolonged siege.
Perhaps the most famous use of the field gun in terms of advanced tactics was Napoleon Bonaparte's use of very large wheels on the guns that allowed them to be moved quickly even during a battle. By moving the guns from point to point during a battle, enemy formations could be broken up to be handled by the infantry or cavalry wherever they were massing, dramatically increasing the overall effectiveness of the attack.
World War I
As the evolution of artillery continued, almost all guns of any size became capable of being moved at some speed. With few exceptions, even the largest siege weapons had become mobile by road or rail by the start of World War I, and evolution after that point tended to be towards smaller weapons with increased mobility. Even the German super-heavy guns in World War II were rail or caterpillar-track mobile.In British use, field guns or light guns were anything up to in calibre, larger calibres were medium guns, and the largest calibres were heavy guns.
World War II
Since about the start of World War II, the term has been applied to long-range artillery pieces that fire at a relatively low angle, as opposed to howitzers which can fire at higher angles. Field guns also lack a specialized purpose, such as anti-tank or coastal artillery. By the later stages of World War II the majority of artillery in use was either in the form of howitzers of to, or in form of hybrid anti-tank/field guns that had high enough muzzle velocity to be used in both roles. The most common field guns of the era were the British, the American 155 mm Long Tom and the Soviet BS-3 - an artillery piece adapted from a naval gun and designed to double up as an anti-tank weapon.One of the most produced field guns during the war was the Soviet ZiS-3 with over 103,000 produced. The ZiS-3 could be used in direct fire against armored vehicles, direct fire in infantry support, and indirect fire against distant targets.