Deflection (ballistics)

Deflection is a technique used for effectively propelling a projectile at a moving target, also known as "leading the target", i.e. 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 time the projectile would take to reach the target's range. This can become the case over long distances (e.g. a distant target for a skilled sniper), due to fast moving targets (e.g. an opposing aircraft in an aerial dogfight), or while using relatively slow projectiles (e.g. a crossbow bolt or a basketball thrown to a running teammate). During World War II, U.S. Navy pilots were taught explicitly about the concept in order to capitalize on the advantages of the F4F Wildcat.

Modern day fighter aircraft have automated deflection sights, where a computer calculates lead and projects the solution onto a heads up display (HUD). The visual assistance with targeting the gun is offset by the enormous speed and agility of modern aircraft, compared to the days when targeting was less advanced.

In artillery, deflection is also used against fixed targets to compensate for windage and range. Due to the Earth's rotation, surface points have different velocities and curved motion, leading to apparent Coriolis drift of a long-range target.

Leading targets is the practice of aiming one's weapon ahead of the target so that the projectile will hit its mark. Over reasonably short ranges, leading is typically unnecessary when using firearms, but it is still relevant for sniping where the bullet may take a second or more to reach its target, as well as for weapons such as bows that use lower-velocity projectiles. It is generally unnecessary for guided 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.

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