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In field artillery, the accuracy of indirect fire depends on the use of aiming points. [1] In air force terminology the aiming point (or A.P.) refers to holding the intersection of the cross hairs on a bombsight 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. 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.
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 paralloscope, 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.
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, AS90 and Panzerhaubitze 2000, and subsequently they were adopted for towed guns, notably UK's 105mm L118 Light Guns.
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 sieges, and led to heavy, fairly immobile siege engines. As technology improved, lighter, more mobile field artillery cannons developed for battlefield use. This development continues today; modern self-propelled artillery vehicles are highly mobile weapons of great versatility generally providing the largest share of an army's total firepower.
Self-propelled artillery is artillery equipped with its own propulsion system to move toward its firing position. Within the terminology are the self-propelled gun, self-propelled howitzer, self-propelled mortar, and rocket artillery. They are high mobility vehicles, usually based on continuous tracks carrying either a large field gun, howitzer, mortar, or some form of rocket/missile launcher. They are usually used for long-range indirect bombardment support on the battlefield.
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.
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 by observing the fall of shot and calculating new angles.
External ballistics or exterior ballistics is the part of ballistics that deals with the behavior of a projectile in flight. The projectile may be powered or un-powered, guided or unguided, spin or fin stabilized, flying through an atmosphere or in the vacuum of space, but most certainly flying under the influence of a gravitational field.
An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a tilt indicator, tilt sensor, tilt meter, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch & roll indicator. Clinometers measure both inclines and declines using three different units of measure: degrees, percentage points, and topos. The astrolabe is an example of an inclinometer that was used for celestial navigation and location of astronomical objects from ancient times to the Renaissance.
Point-blank range is any distance over which a certain firearm can hit a target without the need to compensate for bullet drop, and can be adjusted over a wide range of distances by sighting in the firearm. If the bullet leaves the barrel parallel to the sight, the bullet, like any object in flight, is pulled downwards by gravity, so for distant targets, the shooter must point the firearm above the target to compensate. But if the target is close enough, bullet drop will be negligible so the shooter can aim the gun straight at the target. If the sights are set so that the barrel has a small upward tilt, the bullet starts by rising and later drops. This results in a weapon that hits too low for very close targets, too high for intermediate targets, too low for very far targets, and point blank at two distances in between. For a .270 Winchester, as an example, the bullet first crosses the line of sight at about 23 metres as it is rising and has a maximum impact above the line of sight of approximately 75 mm and crosses the line of sight again at about 250 metres. This is for a 130 grain hunting bullet. Therefore point blank range for a deer size target is about 275 metres . Point-blank range will vary by a weapon's external ballistics characteristics and the allowable error at the target; the flatter the bullet's trajectory or the larger the target, the longer the point-blank range will be.
A fire-control system (FCS) is a number of components working together, usually a gun data computer, a director and radar, which is designed to assist a ranged weapon system to target, track, and hit a target. It performs the same task as a human gunner firing a weapon, but attempts to do so faster and more accurately.
Counter-battery fire is a battlefield tactic employed to defeat the enemy's indirect fire elements, including their target acquisition, as well as their command and control components. Counter-battery arrangements and responsibilities vary between nations but involve target acquisition, planning and control, and counter-fire. Counter-battery fire rose to prominence in World War I.
A counter-battery radar or weapon tracking radar is a radar system that detects artillery projectiles fired by one or more guns, howitzers, mortars or rocket launchers and, from their trajectories, locates the position on the ground of the weapon that fired it. Such radars are a subclass of the wider class of target acquisition radars.
A milliradian 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 the angle of the sight compared to the barrel. Milliradians are also used for comparing shot groupings, or to compare the difficulty of hitting different sized shooting targets at different distances. When using a scope with both mrad adjustment and a reticle with mrad markings, the shooter can use the reticle as a ruler to count the number of mrads a shot was off-target, which directly translates to the sight adjustment needed to hit the target with a follow-up shot. Optics with mrad markings in the reticle can also be used to make a range estimation of a known size target, or vice versa, to determine a target size if the distance is known, a practice called "milling".
In ballistics, the elevation is the angle between the horizontal plane and the axial direction of the barrel of a gun, mortar or heavy artillery. Originally, elevation was a linear measure of how high the gunners had to physically lift the muzzle of a gun up from the gun carriage to compensate for projectile drop and hit targets at a certain distance.
Field artillery is a category of mobile artillery used to support armies in the field. These weapons are specialized for mobility, tactical proficiency, short range, long range, and extremely long range target engagement.
A prism paralleloscope is a piece kit used by artillery units as a gun aiming point. It is a type of paralleloscope that uses a prism instead of a plain mirror. Its purpose was to function as an aiming point in the horizontal plane when laying for indirect fire artillery.
MT-12 or 2A29 is a Soviet smoothbore 100-mm anti-tank gun, which served as the primary towed anti-tank artillery in the Soviet army from the early 1970s to the late 1980s. It is in significant use in the Russo-Ukrainian War (2014-present).
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 type of ammunition.
Gun laying is the process of aiming an artillery piece or turret, such as a gun, howitzer, or mortar, on land, in air, or at sea, against surface or aerial targets. It may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire, where firing data is calculated and applied to the sights. The term includes automated aiming using, for example, radar-derived target data and computer-controlled guns.
A gun carriage is a frame or a mount that supports the gun barrel of an artillery piece, allowing it to be maneuvered and fired. These platforms often had wheels so that the artillery pieces could be moved more easily. Gun carriages are also used on ships to facilitate the movement and aiming of large cannons and Guns. These are also used in the funeral procession of any higher authority of any state and country.
The depression range finder (DRF) was a fire control device used to observe the target's range and bearing to calculate firing solutions when gun laying in coastal artillery. It was the main component of a vertical base rangefinding system. It was necessitated by the introduction of rifled artillery from the mid-19th century onwards, which had much greater ranges than the old smoothbore weapons and were consequently more difficult to aim accurately. The DRF was invented by Captain H.S.S. Watkin of the Royal Artillery in the 1870s and was adopted in 1881. It could provide both range and bearing information on a target. The device's inventor also developed a family of similar devices, among them the position finder, which used two telescopes as a horizontal base rangefinding system, around the same time; some of these were called electric position finders. Some position finders retained a depression range finding capability; some of these were called depression position finders. Watkin's family of devices were deployed in position finding cells, a type of fire control tower, often in configurations that allowed both horizontal base and vertical base rangefinding. Watkin's system included automatic electrical updating of range and bearing dials near the guns as the position finders were manipulated, and a system of remotely firing the guns electrically from the position finding cell. The improved system was trialled in 1885 and widely deployed in the 1890s. Functionally equivalent devices were developed for the United States Army Coast Artillery Corps and its predecessors, called depression position finders or azimuth instruments depending on function, adopted in 1896 and deployed widely beginning in the early 1900s as the Endicott program of modern coastal defences was built. These devices were also used by both countries to control submarine (underwater) minefields.
In ranged weapons such as firearms and artillery pieces, sighting in or sight-in is a preparatory or corrective calibration of the sights with the goal that the projectile may be placed at a predictable impact position within the sight picture. The principle of sighting-in is to shift the line of aim until it intersects the parabolic projectile trajectory at a designated point of reference, so when the gun is fired in the future it will repeatably hit where it aims at identical distances of that designated point.