Gun Laying - Description

Description

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. 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. The dividing angle between the trajectories is about 45 degrees, it varies slightly due to gun dependent factors. Below 45 degrees the trajectory is called "low angle" (or lower register), above is "high angle" (or upper register). The differences are that low angle fire has a shorter time of flight, a lower vertex and flatter angle of descent.

All guns have carriages or mountings that support the barrel assembly (called the ordnance in some countries). Early guns could only be traversed by moving their entire carriage or mounting, and this lasted with heavy artillery into World War II. Mountings could be fitted into traversing turrets on ships, coast defences or tanks. From circa 1900 field artillery carriages provided traverse without moving the wheels and trail.

The carriage, or mounting, also enabled the barrel to be set at the required elevation angle. With some gun mounts it is possible to depress the gun, i.e. move it in the vertical plane to point it below the horizon. Some guns require a near-horizontal elevation for loading. An essential capability for any elevation mechanism is to prevent the weight of the barrel forcing its heavier end downward. This is greatly helped by having trunnions (around which the elevating mass rotates vertically) at the centre of gravity, although a counterbalance mechanism can be used. It also means the elevation gear has to be strong enough to resist considerable downward pressure but still be easy for the gun layer to use.

Until recoil systems were invented in the late 19th century and integrated into the gun carriage or mount, guns moved substantially backwards when they fired, and had to be moved forward before they could be laid. However, mortars, where the recoil forces were transferred directly into the ground (or water, if mounted on a ship), did not always require such movement. With the adoption of recoil systems for field artillery, it became normal to pivot the saddle on the lower carriage, initially this "top traverse" was only a few degrees but soon offered a full circle, particularly for anti-aircraft guns. The introduction of recoil systems was an important milestone.