Gun laying

Gun laying is the process of aiming an artillery piece or turret, such as a gun, howitzer, or mortar, on land, in air, or at sea, against surface or aerial targets. It may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire, where firing data is calculated and applied to the sights. The term includes automated aiming using, for example, radar-derived target data and computer-controlled guns. Gun laying is a set of actions to align the axis of a gun barrel so that it points in the required direction. This alignment is in the horizontal and vertical planes. A gun is "traversed" (rotated in a horizontal plane) to align it with the target, and "elevated" (moved in the vertical plane) to range it to the target. Gun laying may be for direct fire, where the layer sees the target, or indirect fire, where the target may not be visible from the gun. Gun laying has sometimes been called "training the gun". Laying in the vertical plane (elevation angle) uses data derived from trials or empirical experience. For any given gun and projectile types, it reflects the distance to the target and the size of the propellant charge. It also incorporates any differences in height between gun and target. With indirect fire, it may allow for other variables as well. With direct fire, laying in the horizontal plane is merely the line of sight to the target, although the layer may make allowance for the wind, and with rifled guns the sights may compensate for projectile "drift". With indirect fire the horizontal angle is relative to something, typically the gun's aiming point, although with modern electronic sights it may be a north-seeking gyro. Depending on the gun mount, there is usually a choice of two trajectories that will result in the shot landing in the same spot. The dividing angle between the trajectories is about 45 degrees (usually between 0 degrees and 90 degrees), it varies slightly due to gun dependent factors. Below 45 degrees the trajectory is called "low angle" (or lower register), above 45 degrees is "high angle" (or upper register).