Aim Point
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{{Unreferenced, date=April 2007 In field
artillery Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during siege ...
, the accuracy of
indirect fire Indirect fire is aiming and firing a projectile without relying on a direct line of sight between the gun and its target, as in the case of direct fire. Aiming is performed by calculating azimuth and inclination, and may include correcting aim ...
depends on the use of aiming points. In
air force An air force – in the broadest sense – is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an ...
terminology the aiming point (or A.P.) refers to holding the intersection of the cross hairs on a
bombsight A bombsight is a device used by military aircraft to drop bombs accurately. Bombsights, a feature of combat aircraft since World War I, were first found on purpose-designed bomber aircraft and then moved to fighter-bombers and modern tactical ...
when fixed at a specific target. An indirect fire aiming point provides a point of angular reference to aim a gun in the required horizontal direction –
azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...
. Until the 1980s aiming points were essential for indirect fire artillery. They are also used by mortars and machine guns firing indirectly. An essential requirement of an aiming point is that it be at a sufficient distance from the gun using it. The reason for this is that, while firing, guns, particularly towed guns, move back a short distance – perhaps a foot, as their spades embed and may move more in soft ground. When they traverse their barrels their sights also move because they are not at the point of pivot. All this means that if the aiming point is too close then the angle to the aiming point changes. This aims the guns off-target, possibly up to several hundred meters. For gun-laying purposes a distance of a few kilometers from gun to aiming point is sufficient. An aiming point would be a sharply defined and easily distinguished feature, such the edge of an obvious building. However, this presents problems in featureless areas, in bad visibility or at night and putting lights on distant aiming points is seldom practical. Therefore, methods of simulating a distant aiming point are required.


History

The earliest form of aiming point was a pair of aiming posts for each gun, almost in line with one another when viewed through the gun's sight, and placed about 50 meters from the gun. There were at least two ways of using these, but the simplest is to aim the sight midway between them. Before the First World War the French introduced the collimateur. During that war the British introduced their first parallescope, which was a horizontal mirror placed a few feet from the gun; the layer aimed his sight at its reflection. In the 1950s the parallescope was replaced by the prism parallescope that was more robust and easily positioned. In the 1970s the US introduced a modern version of the French device and called it a collimator. In the same period infra-red beacons had some very limited use. In some special circumstances, such as when only one round or salvo was going to be fired (e.g. by nuclear artillery or a multiple rocket launcher), a director or aiming circle about 100 meters away could be used as an aiming point.


Related matters

Originally, when indirect fire was introduced, an aiming point (AP) was used as a quick means of orienting the guns by ordering an angle to the AP for all guns to use. Other aiming points were used for aiming while firing, initially called ‘supplementary aiming points’ were given the name ‘Gun Aiming Points’ (GAP). Many armies required that each gun recorded several GAPs, some mounted recording plates on their guns where the GAP angles were written, and some had regulations giving the priority order for the use of different types of GAP. In the 1980s the US Multi-Launch Rocket System entered US service, this did not use GAPs because it had a gyroscopic orientation system and did not need external reference points or orientation. During the 1990s similar systems were adopted by
M109 Paladin The M109 is an American 155 mm turreted self-propelled howitzer, first introduced in the early 1960s to replace the M44. It has been upgraded a number of times, most recently to the M109A7. The M109 family is the most common Western indirect-fi ...
,
AS90 The AS-90 ("Artillery System for the 1990s"), known officially as Gun Equipment 155 mm L131, is an armoured self-propelled artillery weapon used by the British Army. It can fire standard charges up to using 39 calibre long barrel (comp ...
and
Panzerhaubitze 2000 The Panzerhaubitze 2000 ("tank howitzer 2000"), () abbreviated PzH 2000, is a German 155 mm self-propelled howitzer developed by Krauss-Maffei Wegmann (KMW) and Rheinmetall in the 1980s and 1990s for the German Army. It is capable of a very h ...
, and subsequently they were adopted for towed guns, notably UK’s 105mm
L118 Light Gun The L118 light gun is a 105 mm towed howitzer. It was originally designed and produced in England for the British Army in the 1970s. It has since been widely exported. The L119 and the United States Army's M119 are variants that use a different ...
s.


See also

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Milliradian A milliradian ( SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting t ...
Ballistics