Glossary

Angle of Departure.—The angle which the line of departure makes with the horizontal plane, in other words, the quadrant angle plus the jump. FAT 142

Angle of Descent.—The angle which the trajectory makes with the line of sight at the point of their second intersection. FAT 143

Angle of Incidence.—The angle which the trajectory makes with the normal to the surface struck. FAT 143

Angle of Elevation.—The angle which the line of sight makes with the axis of the gun. FAT 143

Angle of Sight.—The angle which the line of sight makes with the horizontal plane. FAT 143

Axis of the Gun.—A line passing down the centre of the bore.  FAT 143

Axis of the Trunnions.—A line passing through the centre of the trunnions. FAT 143

Battery Angle.—The angle formed at the battery by imaginary lines drawn to the target and the observing station. FAT 143

Calibre.—The diameter of the bore in inches measured across the lands. FAT 143

Clinometer.— An instrument showing the angle of elevation (qv) OED. The Manual of the 18 pounder identifies a “sight clinometer” which provides the angle of sight (qv) over a range of forty degrees (20 degrees elevation or 20 degrees depression). Manual 18 pdr. 16

Degree.— A measurement of angle. There are 360 degrees in a circle. See also minute.

Drift.—The constant deflection of the shell due to the rotation imparted by the rifling. FAT 143

Direct Laying.—When the gun is laid by looking over or through the sights at the target. FAT 143

Firing battery.—Six guns and 6 ammunition wagons, except in the case of 4-gun batteries, when it consists of 4 guns and 4 wagons. FAT 3

Fuze or fuse.—The device which detonates the bursting charge, either on impact or at a timed interval in the air, as required.

Fuze indicator.— A instrument rather like a slide rule, which gives the “correct fuze setting for effective burst at any range, when once the instrument has been adjusted for one range.” FAT 162

Gunnery.— The science of directing a projectile so that it will strike a given object. FAT 145

Indirect Laying.—When the gun is laid for direction on an aiming point, or on aiming posts, the angle of sight is adjusted by clinometer and the elevation by the range indicator or drum. FAT 143

Jump.—The angle between the line of departure and the axis of the piece before firing. It is due to the vertical movement of the gun on firing, and for any gun differs according to the mounting and the charge used. FAT 143

Lateral Deviation.—The distance of the point of impact of the projectile right or left of the line of fire. FAT 143

Lay  (as in Gun-Laying) .— A gun is said to be ‘laid,’ when, by elevating and traversing, its axis is made to point in the required direction. FAT 172. Loosely used as a synonym for “aim,” the term “lay” reminds us that it is not just a matter of adjusting the barrel, but of putting the whole gun in the right position.

Line of Departure.—The direction of the shell on leaving the muzzle. FAT 143

Line of Fire.—A line joining the muzzle of the piece and the target. FAT 144

Line of Sight.—A straight line passing through the sights and the point aimed at. FAT 144

Minute.— A measurement of an angle: there are sixty minutes in one degree of an angle.

Muzzle Velocity.—The velocity in feet per second with which a shell leaves the muzzle. FAT 144

Point Blank.—A gun is laid point blank when the line of sight is parallel to its axis. FAT 144

Quadrant Angle.—The angle which the axis of the piece makes with the horizontal plane. It is termed quadrant elevation or depression according as the gun is laid above or below the horizontal plane. The angle of elevation and the quadrant angle are the same when the line of sight is horizontal. FAT 144

Range.—The distance to the second intersection of the trajectory with the line of sight. FAT 144

Ranging.—Ranging is the process of finding the elevation, fuze, and line. FAT 144

Remaining Velocity.—The velocity of a shell at any given point of its trajectory. FAT 144

Section.—A section consists of two subsections. FAT 5

Striking Velocity.—The velocity of a shell at the point of impact. FAT 144

Subsection.— (“Sub,” identified by a letter of the alphabet, as in D Sub.) One gun, with its complement of men, horses, and ammunition wagons. FAT 5

Trajectory.—The curve described by the shell in its flight. FAT 144

Traverse.—The movement of the gun in a horizontal plane. The gun is equipped with a traversing gear, or it could be physically moved by being pivoted on its trail.