Deflection (military)
Encyclopedia
Deflection is a technique used for effectively firing a ranged weapon at a moving target, that describes "leading the target"; that is, shooting ahead of a moving target so that the target and projectile will collide. This technique is only necessary when the target will have moved a sufficient distance to fully displace its position during the period of time of the projectile would take to reach the target's range. This can become the case either over long distances (such as a distant target for a skilled sniper), due to fast moving targets (such as an opposing aircraft in an aerial dogfight
Dogfight
A dogfight, or dog fight, is a form of aerial combat between fighter aircraft; in particular, combat of maneuver at short range, where each side is aware of the other's presence. Dogfighting first appeared during World War I, shortly after the invention of the airplane...

), or using slow projectiles, such as a crossbow
Crossbow
A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts or quarrels. The medieval crossbow was called by many names, most of which derived from the word ballista, a torsion engine resembling a crossbow in appearance.Historically, crossbows played a...

 bolt or an arrow from a bow
Bow (weapon)
The bow and arrow is a projectile weapon system that predates recorded history and is common to most cultures.-Description:A bow is a flexible arc that shoots aerodynamic projectiles by means of elastic energy. Essentially, the bow is a form of spring powered by a string or cord...

. During World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, U.S. Navy pilots were taught explicitly on the concept in order to capitalize on the advantages of the F4F Wildcat
F4F Wildcat
The Grumman F4F Wildcat was an American carrier-based fighter aircraft that began service with both the United States Navy and the British Royal Navy in 1940...

.

In artillery
Artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

, deflection is also used even against fixed targets to compensate for windage
Windage
Windage is a force created on an object by friction when there is relative movement between air and the object.There are two causes of windage:# the object is moving and being slowed by resistance from the air...

 and range. Due to Earth's rotation, surface points have different velocities and curved motion, leading to apparent Coriolis
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

 drift of a long-range target.

Leading targets is the practice of aiming one's weapon ahead of his or her target so that the projectiles will hit their mark. Over reasonably short ranges, leading is typically unnecessary when using firearm
Firearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

s, but it is still relevant for sniping (where the bullet may take up to a second or more to reach its target), as well as for weapons such as bow
Bow (weapon)
The bow and arrow is a projectile weapon system that predates recorded history and is common to most cultures.-Description:A bow is a flexible arc that shoots aerodynamic projectiles by means of elastic energy. Essentially, the bow is a form of spring powered by a string or cord...

s that use lower-velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...

 projectiles. It is generally unnecessary for guided
Missile guidance
Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile's target accuracy is a critical factor for its effectiveness...

 projectiles, although the autonomous guiding mechanism may be designed to calculate a flight path to lead its targets on its own, to ensure an interception.

Computer games

Modern computer games of the first-person shooter
First-person shooter
First-person shooter is a video game genre that centers the gameplay on gun and projectile weapon-based combat through first-person perspective; i.e., the player experiences the action through the eyes of a protagonist. Generally speaking, the first-person shooter shares common traits with other...

 genre typically feature a number of relatively low-velocity projectile weapons, such as unguided shoulder-launched missile weapon
Shoulder-launched missile weapon
A shoulder-fired missile, shoulder-launched missile or man-portable missile is a projectile fired at a target, small enough to be carried by a single person, and fired while held on one's shoulder...

s, so leading targets is relevant to them as well. Additionally, in some multiplayer game
Multiplayer game
A multiplayer video game is one which more than one person can play in the same game environment at the same time. Unlike most other games, computer and video games are often single-player activities that put the player against preprogrammed challenges and/or AI-controlled opponents, which often...

s that calculate behaviour on a remote server, even for high-velocity or hitscan
Hitscan
Hitscan is a term that is used mainly in computer games. It is a test to find out what can be hit by an in-game weapon...

 weapons, there are issues of latency
Latency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...

 that may require leading. Essentially, even if the shooter has the target exactly in his sights, by the time the information relating weapon fire from the shooter's computer has reached the server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

, the target may have moved enough to avoid the shot.

QuakeWorld
QuakeWorld
QuakeWorld is an update to id Software's seminal multiplayer deathmatch game, Quake, that enhances the game's multiplayer features to allow people with dial-up modems to achieve greatly improved responsiveness when playing on Internet game servers...

 and the Source engine
Source engine
Source is a 3D game engine developed by Valve Corporation. It debuted in June 2004 with Counter-Strike: Source and shortly thereafter Half-Life 2, and has been in active development ever since...

, among others, use a lag compensation system which moves all players back to a point in time based on the shooters client interpolation time and ping
Ping
Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...

. Such systems eliminate the need to lead hitscan weapons, but introduce the risk of players perceptibly being shot after taking cover.
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