Editing Indirect fire (section)

==Description==
Indirect fire is most commonly used by [[field artillery]] and [[Mortar (weapon)|mortars]] (although field artillery was originally and until after World War I a direct fire weapon, hence the bullet-shields fitted to the carriages of guns such as the famous [[Canon de 75 modèle 1897|M1897]] 75&nbsp;mm). It is also used with [[missile]]s, [[howitzer]]s, [[rocket artillery]], [[multiple rocket launcher]]s, [[cruise missile]]s, [[ballistic missile]]s, naval guns against shore targets, sometimes with [[machine guns]], and has been used with [[tank gun|tank]] and [[anti-tank gun]]s and by anti-aircraft guns against surface targets. 

There are two dimensions in aiming a weapon:
* In the horizontal plane (azimuth); and
* In the vertical plane (elevation), which is governed by the distance (range) to the target and the energy of the propelling charge.

The projectile [[trajectory]] is affected by atmospheric conditions, the velocity of the projectile, the difference in altitude between the firer and the target, and other factors. Direct fire sights may include mechanisms to compensate for some of these. [[Handguns]] and [[rifle]]s, machine guns, anti-tank guns, tank main guns, many types of [[Rocket (weapon)|unguided rockets]],  and guns mounted in [[close air support|aircraft]] are examples of weapons primarily designed for ''direct'' fire.

NATO defines indirect fire as "Fire delivered at a target which cannot be seen by the aimer."<ref>AAP-6 ''NATO Glossary of Terms and Definitions''</ref> The implication is that azimuth and/or elevation 'aiming' is done using instrumental methods. Hence indirect fire means applying 'firing data' to azimuth and elevation sights and laying these sights. Longer range uses a higher trajectory, and in theory maximum range is achieved with an elevation angle of 45 degrees.<ref>{{cite book|url=https://books.google.com/books?id=EuXwNgfI5SwC&pg=PA196|title=Lightning Over Water: Sharpening America's Light Forces for Rapid-Reaction Missions|author=John Matsumura|page=196|publisher=Rand Corporation|year=2000|isbn=0-8330-2845-6}}</ref><ref>{{cite book|url=https://books.google.com/books?id=I5-I-AaTNYMC&pg=PA24|title=When Reason Fails: Portraits of Armies at War: America, Britain, Israel and the Future|author=Michael Goodspeed|page=24|publisher=Greenwood Publishing Group|year=2002|isbn=0-275-97378-6}}</ref><ref>{{cite book|url=https://books.google.com/books?id=AoIsUnTgQHQC&pg=PA242|title=Artillery: An Illustrated History of its Impact|author=Jeff Kinard|page=242|isbn=978-1-85109-556-8|publisher=ABC-CLIO|year=2007}}</ref>

{{anchor|Call for fire}}[[File:785px Arty Call for Fire 1.jpg|thumb|right|400px|Calling and adjusting indirect artillery fire on a target unseen to the soldiers manning the guns, a modern United States example]]

It is reasonable to assume that original purpose of indirect fire was to enable fire from a 'covered position', one where gunners can not be seen and engaged by their enemies (that and as the range of artillery lengthened, it was impossible to see the target past all the intervening terrain). The concealment aspect remains important, but from World War I equally important was the capability to concentrate the fire of many artillery batteries at the same target or set of targets. This became increasingly important as the range of artillery increased, allowing each battery to have an ever-greater area of influence, but required command and control arrangements to enable concentration of fire. The physical laws of [[ballistics]] means that guns firing larger and heavier projectile can send them farther than smaller-calibre guns firing lighter shells. By the end of the 20th century, the typical maximum range for the most common guns was about 24 to 30&nbsp;km, up from about 8&nbsp;km in World War I.

During World War I, covered positions moved farther back and indirect fire evolved to allow any point within range to be attacked, ''firepower mobility'', without moving the firers. If the target cannot be seen from the gun position, there has to be a means of identifying targets and correcting aim according to fall of shot. The position of some targets may be identified by a headquarters from various sources of information (spotters): [[Artillery observer|observers]] on the ground, in aircraft, or in [[observation balloon]]s. The development of [[Telecommunications|electrical communication]] immensely simplified reporting, and enabled many widely dispersed firers to concentrate their fire on one target.

The trajectory of the projectile could not be altered once fired, until the introduction of [[smart munition]]s.