Indirect fire

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Indirect shot: Steep fire - Upper angle group

Indirect fire is a military term. It describes an alignment procedure in which the target is not visible from the firing position of a weapon system and therefore has to be sighted indirectly via an auxiliary target or a shooting basis has to be determined from map data . The target reconnaissance takes place from an observation point away from the fire position. Artillery and mortars usually fire indirectly.


The technical prerequisite for indirect straightening is the possibility of ascertaining the pipe elevation from the horizontal and the deviation between the firing direction and the basic direction using an independent line of sight. The ballistic trajectory of a projectile is also influenced by the muzzle velocity (size of the propellant charge, charge temperature, tube wear), the atmospheric conditions (wind, air density), the difference in altitude between the gun and the target and the rotation of the earth ( Coriolis effect). Firing boards for indirect fire therefore usually give values ​​for correcting a number of influencing factors. If these factors are not taken into account, there can be considerable deviations between the aiming point and the point of impact, especially with long firing ranges. For this reason and because of possible inaccuracies in determining the direction and distance, zeroing may be necessary.

Since the target cannot be seen from the firing position with indirect fire, target data must be passed on from an observation point to the firing position. The simplest procedure requires an auxiliary target (mountain peak, church tower, etc.) that is visible from the fire and observation point and an observation point positioned close to the firing position: In this case, the sight can be aligned with the auxiliary target, which indicates the basic direction. The observation point then reports the lateral deviation from the basic direction and the distance from which the necessary pipe elevation is determined according to a shooting board. If the observation point is at a greater distance, the angular deviation to the target between observation and firing position must be determined and compensated for by means of two directional circles in the firing position and the observation point. If the observation point cannot be seen from the firing position, its relative position must be determined trigonometrically . Alternatively, the position of the fire, the observation point and, through the latter, the target can also be defined in a geographic reference system (e.g. UTM coordinate system ).

Development and tactics

Indirect straightening methods allow a more favorable choice of the firing position and greater mobility of the fire, since a line of sight between the target and the firing position is not necessary. The gun can therefore be in a position that is better protected from sight and the effects of fire, and its range of fire can be used to the maximum, provided observation points are available. The use of indirect straightening methods is opposed to the high level of effort involved in calculating the shooting basis and the need for secure telecommunication connections between observation and fire positions.

Until the end of the 19th century, indirect aiming for artillery was largely restricted to the fortress guns . This changed with the introduction of drawn pipes, smokeless powder , pipe return systems and rapid fire closures, first combined in the French Canon de 75 mm modèle in 1897 . Due to the high firepower of such weapons, the previously preferred approach of artillery in open firing positions had become dangerous. Nevertheless, the indirect straightening method was still controversial until the beginning of the First World War , but then finally prevailed and was also often used when using heavy machine guns . During this war, the process was improved by taking account of the daily atmospheric influences. Thanks to the procedure developed by Georg Bruchmüller , it was now possible to open fire without shooting in and thus surprisingly.

In the interwar period, the communications equipment of the artillery was improved. Forward observers equipped with radio equipment and able to follow the infantry on the battlefield went to the observation posts , which were equipped with wire connections for firing positions and unsafe means of requesting fire, such as signal rockets . This made flexible management of indirect fire possible, where in the First World War it was still often necessary to shoot according to a rigid fire plan.

After the Second World War, the introduction of fire control computers accelerated fire control, especially that of the combined fire of several units. With the introduction of satellite navigation systems in recent decades, the need to manually measure the firing positions of the artillery has been eliminated. Since then, firing positions can be obtained more quickly, which is particularly favorable to the mobile fighting style of the artillery equipped with self-propelled guns. Readjusted precision ammunition has been in use since the 1990s. It reduces the dispersion and increases the accuracy of the artillery, whereby the ammunition expenditure and collateral damage can be reduced. In the case of laser-guided ammunition, it extends the tasks of the artillery observer to include target lighting.

See also

Individual evidence

  1. ^ Frank W. Sweet: The Evolution of Indirect Fire . Backintyme, 2000, ISBN 978-0-939479-20-7 , pp. 1 ff . ( limited preview in Google Book Search [accessed February 21, 2017]).