Indirect Fire - Description

Description

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 rifles, tank guns, rockets, and guns mounted in 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." 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. Indirect fire can be used when the target is visible from the firing position. However, it is mostly used when the target is at longer range and invisible to the firer due to the terrain. Longer range uses a higher trajectory and in theory maximum range is achieved with an elevation angle of 45 degrees.

Indirect fire is most commonly associated with field artillery. It is also used with mortars and naval guns against shore targets, sometimes with machine guns and has been used with tank and anti-tank guns and by anti-aircraft guns against surface targets.

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. The concealment aspect remains important but from World War I equally important was the capability to concentrate the fire of many 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 further 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 km, up from about 8 km in World War I.

If the target cannot be seen from the gun position, there has to be some other means of telling the guns what, where and when to fire. This may be from a ground or air observer, or from a headquarters identifying targets from various sources of information.

During World War I, covered positions moved further back and indirect fire evolved to allow any point within range to be attacked – firepower mobility – without moving the firers. The concept of firepower mobility flowered with the arrival of radio communications that allowed target acquirers to be anywhere on the ground or in the air and communicate with the firers. It also enables many widely dispersed firers to concentrate their fire on one target.

The essence of traditional indirect fire is that the trajectory of the projectile cannot be altered once it has been fired. However, some projectiles with a guidance system operate by keeping to the trajectory they were fired on.