Direct fire
Direct fire refers to the launching of a projectile directly at a target on a relatively flat trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...

. The firing weapon must have a sighting device
Sight (device)
A sight is a device used to assist aligning or aim weapons, surveying instruments, or other items by eye. Sights can be a simple set or system of markers that have to be aligned together as well as aligned with the target...

 and an unobstructed line of sight to the target, which means no objects or friendly units can be between it and the target. A weapon engaged in direct fire exposes itself to return fire from the target.

By contrast, indirect fire
Indirect fire
Indirect fire means aiming and firing a projectile in a high trajectory without relying on a direct line of sight between the gun and its target, as in the case of direct fire...

 refers to firing projectile on a high ballistic trajectory, and does not need a direct line of sight to the target because the shots are normally directed by a forward observer
Artillery observer
A military artillery observer or spotter is responsible for directing artillery fire and close air support onto enemy positions. Because artillery is an indirect fire weapon system, the guns are rarely in line-of-sight of their target, often located tens of miles away...

. As such, indirect fire weapons can shoot over obstacles or friendly units and the weapons be can be concealed from direct return fire.

Example of direct fire weapons include handgun
A handgun is a firearm designed to be held and operated by one hand. This characteristic differentiates handguns as a general class of firearms from long guns such as rifles and shotguns ....

s, rifle
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

s, machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

s, anti-tank guns, and anti-tank rockets. Howitzers and mortars are examples of indirect fire weapons. Large caliber machine guns, like the .50 caliber, can be used in both roles. In the pre-gun age, bows could be used in either role.

For unguided projectiles, direct fire is generally more accurate and of higher velocity and thus is better for penetrating hardened targets and for quickly destroying small, discrete targets. As a general rule, direct fire - especially that from foot soldiers - is required to dislodge enemy units from an area; indirect fire can repress a target area as soldiers and armored vehicles close in on it, but indirect fire cannot capture a target on its own.
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