Indirect fire is a military term for battlefield weapons fired without a direct line of sight on their target. This allows them to fire over obstacles, and also to engage targets at greater range than can direct fire weapons. The most common indirect fire weapons are mortars, howitzers, and multiple rocket launchers.
While some types of weapons, such as mortars and howitzers, are most commonly used in an indirect fire role, indirect fire is a technique as well as a type of weapon. Howitzers, for example, can be depressed to a horizontal position and fired "over open sights", typically in final defense of the howitzer position.
Indirect fire trajectories
The basic trajectory of an indirect fire weapon is a parabola. Computing such a trajectory is much simpler for basic mortar and howitzer rounds, to which all flight energy is imparted by the initial propellant explosion in the weapon's barrel. In this case, the factors include:
- Energy imparted by the propellant
- Shell mass
- Barrel angle (i.e., elevation of the tube)
Of course, air resistance a real-world factor, and includes a number of factors:
- Aerodynamics of the shell
- Barometric pressure
- Features to reduce air resistance, such as base bleed <ref name=GSbasebleed>Base bleed projectiles
Rockets, and specialized shells that are rocket assisted, have much more complex ballistics, since energy continues to be applied during at least part of the trajectory, the thrust-to-weight ratio changes as propellant is turned to gas, and if the thrust is constant or variable.