The directing point (DP) was a term used in the U.S. Coast Artillery to identify a precisely surveyed point that was used as the point of reference for preparing the firing data used to aim the guns of a given

Coast Artillery Coastal artillery is the branch of the armed forces concerned with operating anti-ship artillery or fixed gun batteries in coastal fortifications. From the Middle Ages until World War II, coastal artillery and naval artillery in the form of c ...

battery. Often the DP was taken as the pintle center of the right-most gun in a battery, as an observer looked over the battery towards the sea. In this case, the referenced gun was called the directing gun. In a two-gun battery, the DP was often located at a point midway between the two

guns A gun is a ranged weapon designed to use a shooting tube (gun barrel) to launch projectiles. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, pr ...

(as in the battery illustrated at right). In a four-gun battery, the DP was often located midway between the two central guns. When the guns of a battery were more widely separated, the DP was often taken as a point on the ground perhaps 50 to 100 feet in front of the guns and more or less at the midpoint of the horizontal extent of the battery, visible from all of its guns. An example of such a directing point can be found at

Fort Strong Fort Strong is a former U.S. Army Coast Artillery fort that occupied the northern third of Long Island in Boston Harbor. The island had a training camp during the American Civil War, and a gun battery was built there in the 1870s. The fort was ...

, a Coast Artillery

fort A fortification is a military construction or building designed for the defense of territories in warfare, and is also used to establish rule in a region during peacetime. The term is derived from Latin ''fortis'' ("strong") and ''facere'' ...

Long Island Long Island is a densely populated island in the southeastern region of the U.S. state of New York (state), New York, part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United Sta ...

Boston Harbor Boston Harbor is a natural harbor and estuary of Massachusetts Bay, and is located adjacent to the city of Boston, Massachusetts. It is home to the Port of Boston, a major shipping facility in the northeastern United States. History Since ...

(). Sometimes the DP was marked by a survey disk or a

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

bolt, set by the U.S. Army Engineers (USE) or by the

U.S. Coast and Geodetic Survey The National Geodetic Survey (NGS) is a United States federal agency that defines and manages a national coordinate system, providing the foundation for transportation and communication; mapping and charting; and a large number of applications ...

(USCGS), often in the concrete blast slope or apron or in the ground in front of the

parapet A parapet is a barrier that is an extension of the wall at the edge of a roof, terrace, balcony, walkway or other structure. The word comes ultimately from the Italian ''parapetto'' (''parare'' 'to cover/defend' and ''petto'' 'chest/breast'). Whe ...

of the battery. The photo at left below illustrates a DP like this, between the two guns of Battery Stevenson at Fort Warren in

. Often a target, for example a vertical wooden sighting panel (or a sighting pole, not unlike a

surveyor Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...

's target rod) was placed precisely over the DP marker so that the guns of the battery could sight on it and adjust the offsets of their gun sights. If the guns of a battery were widely separated, the firing data, computed for the DP, might have had to be corrected in

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

for the various guns.Supra, Note 1, at para. 28 ff. Since the azimuths and distances of the guns one from another were known, triangulation could be used to figure out the necessary aiming azimuths for each gun. These calculations could be performed in the

plotting room A plotting room was the co-ordination centre of a fire control system for guns used against enemy ships or aircraft, whether naval guns or coastal artillery. The plotting room received data on ship or aircraft position and motion from fire cont ...

and telephoned to the battery or be performed at the guns. If the guns were relatively close to each other, then it might be enough to point them all at the same azimuth, to fire a

salvo A salvo is the simultaneous discharge of artillery or firearms including the firing of guns either to hit a target or to perform a salute. As a tactic in warfare, the intent is to cripple an enemy in one blow and prevent them from fighting b ...

in parallel with each other.

References

Coastal artillery Artillery operation