Chapter 7 — BASIC FIRE CONTROL 



the horizontal plane, the orange symbolizes the 

 earth, and the point of contact between the two 

 is the point of tangency. Every plane parallel 

 to the horizontal plane Is likewise a horizontal 

 plane. 



Deck Plane 



The deck plane represents the level of the 

 ship's gun mounts. (References to guns include 

 similar weapons systems.) When the ship is 

 level, the horizontal and deck planes coincide, 

 but when the ship rolls and pitches, the deck 

 plane deviates from the horizontal. The stable 

 element measures the amount of angular devia- 

 tion Euid transmits the information to the fire 

 control system. The fire control computer com- 

 pensates for deck tilt by computing a solution 

 in the horizontal plane, then makes train and 

 elevation corrections. What the system does, 

 in effect, is bring the deck plane back to the 

 horizontal. 



Vertical Plane 



A vertical plane is perpendicular to the hori- 

 zontal plane, and is the reference from which 

 bearings are measured. Relative bearing, for 

 example, is measured in the horizontal plane 

 clockwise from the vertical plane through own 

 ship's centerline to the vertical plane through 

 the line of sight. 



The system of planes makes possible the 

 design and construction of mechanical and elec- 

 tronic equipment to solve the fire control problem. 

 These lines and planes are imaginary extensions 

 of some characteristic of the ship or target, 

 or of the relation in space between them. 



FIRE CONTROL NOMENCLATURE 



Fire control nomenclature provides a brief 

 and accurate means of expressing quantities that 

 otherwise would require extended descriptions. 



Two systems of expressing fire control quan- 

 tities presently are effective. The older of the two 

 systems remains in use because some of the 

 earlier fire control equipment, such as the Mk 105, 

 still is in service. With the appearance of new 

 weapons, the old system was found to be inade- 

 quate for expressing the fire control quantities 

 for such ordnance as nr.ssiles. All new weapons 

 systems (such as ASROC), therefore, use the 

 new fire control nomenclature. 



The entire nomenclature is too lengthy and 

 detailed for inclusion in this text, but brief 

 explanations of the two systems are provided 

 so that you may better understand the meaning 



and purpose of the fire control quantities and 

 their symbols. 



A compilation of the nomenclature used in the 

 older antisubmarine fire control systems may be 

 found in ordnance publication OD 3447 and in 

 Sonar Technician G 3 & 2_. 



Old System 



The older system of fire control nomenclature 

 is made up of capital letters that represent basic 

 quantities, and lowercase letters, numerals, the 

 Greek delta (A), and the prime mark ('), used as 

 modifiers to expand the meaning or function of 

 the basic quantity. The capital letter C, for 

 example, is the basic quantity for true course. 

 Own ship is represented by the lowercase letter 

 o; and the target is identified by the letter t. By 

 adding the modifier to the basic quantity, own 

 ship's course becomes Co, and target course is 

 Ct. 



Further expansion of the application of the 

 basic quantity is provided by adding more than 

 one modifier, and placing them both before and 

 after the basic quantity. Thus, B (for bearing) 

 can be modified first to become Br (relative 

 bearing), further to cBr (generated relative 

 bearing), and finally to ^cBr (increments of 

 generated relative bearing). 



The prime modifier (') signifies that the 

 quantity is measured with respect to the deck 

 plane of the ship. Because guns and directors 

 are fastened to the deck of a ship, Br can be 

 measured only at the instant the deck is hori- 

 zontal. Actual values of director train (angles 

 measured in the deck plane are an indication of 

 train, not bearing, in the language of fire control) 

 consequently include a prime mark, signifying that 

 the quantity is measured with respect to the deck 

 plane. As a result, B'r is director train and 

 represents the angle measured from the vertical 

 plane through the fore-and-aft axis of own ship 

 to the vertical plane through the line of sight 

 in the deck plane clockwise from the bow of 

 own ship. 



The Greek delta (^) also is used as a modifier. 

 It is placed before the quantity it modifies, and 

 signifies a change in that quantity during some 

 specific time. It is an increment of a quantity. 



New System 



Ordnance pamphlet OP 1700 has established 

 and standardized the nomenclature used in de- 

 scribing fire control problems and their solu- 

 tions for the control of guns, underwater weapons. 



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