Field gun A field gun is an artillery piece . Originally the term referred to smaller gun s that could accompany a field army on the march and when in combat could be moved about the battlefield in response to changing circumstances ( field artillery ) , as to opposed guns installed in a fort ( garrison artillery / coastal artillery ) , or to siege cannon or mortars which were 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 ' 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 the battle , enemy formations could be broken up to be handled by the infantry wherever they were massing , dramatically increasing the overall effectiveness of the infantry . 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 , a " field gun " was anything up to around 4 . 5 inches in calibre — larger guns were " medium " and the largest of all " heavy " . Their largest gun ( as opposed to howitzer ) was the 5 . 5 inch ( 140 mm ) Medium , with a range of about 15 , 000 \ 16 , 000 yards . 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 howitzer s which can fire at higher angles . By the later stages of World War II the majority of artillery in use was either in the form of howitzers of 105 mm to 155 mm , 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 5 . 5 inch , the U . S . 155 mm Long Tom ( a development of a French World War I weapon ) and Soviet BS - 3 - an artillery piece adopted from a Naval gun and designed to double up as an anti - tank weapon . The 1960s . The U . S . Army tried the long - range gun again in the 1960s with the M107 175 mm gun ; although a high - maintenance item , which after a rash of cracked barrels was removed from service with the U . S . , the M107 was used extensively in the Vietnam War and proved effective in artillery duels with the North Vietnamese forces . Production of the M107 continued through the 1980s , and the gun continues to be in service with the Israeli forces . Modern times . Today the gun finds itself in an area that seems to be gone for good . The class of small and highly mobile artillery has been filled with increasing capacity by the man - portable mortar , which replaced almost every artillery piece smaller than 105 mm . Gun - howitzers fill the middle ground , with the world rapidly standardizing on the 155 mm NATO or 152 mm former USSR standards . The need for a long - range weapon is filled by rocket artillery , or aircraft . Modern gun - artillery such as the L118 105mm light gun is used to provide fire support for infantry and armour at ranges where mortars are impractical . Man - packed mortars lack the range or hitting power of gun - artillery . In between is the rifled towed mortar ; this weapon ( usually in 120mm calibre ) is light enough to be towed by a Land Rover , has a range of over 6 , 000m and fires a bomb comparable in weight to an artillery shell .