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1. BASE COURSE is the selected reference course from which the firing vessel, target (tow), and observing vessels are to maneuver. 2. GENERAL BEARING LINE (G.B.L.) is the true bearing of the enemy ship to be engaged by the flagship of the officer in tactical command, measured from that flagship. 3. The HORIZONTAL is the imaginary plane, tangent to the earth's surface, at the point instantaniously occupied by a surface ship. The ship is considered to move only in the horizontal plane. The horizontal is used as a referance plane from which to measure the relative movemnets of elevated (aerial) targets. 4. The VERTICAL is a plane, perpindicular to a referance plane, passing through a designated line, point or points in the referance plane. If no referance plane is specified it is assumed to be the horizontal, and the "vertical" is then the true vertical plane. 5. The REFERANCE PLANE for a battery is an arbitrarily chosen, imaginary plane, from which the vertical angles of all guns and fire control instruments are measured. It is usually the plane whose inclination to the horizontal is the mean of the inclinations of the turret or mount roller path planes to the horizontal, or a selected director roller path, or the horizontal as determined while checking in drydock. 5a The PHANTOM PLANE is an imaginary plane resulting from combining the inclination from combining the inclination of a turret's roller path to the reference plane with the angular corrections in elevation for the roller path's horizontal displacement from the reference point. 6. LEVEL ANGLE is the angle between reference plane and the horizontal, measured in the plane perpendicular to the reference plane through the line of sight. 7. CROSS-LEVEL ANGLE is the angle between the reference plane and the horizontal, measured in the plane perpendicular to the reference plane at 90 degrees to the plane of the line of sight. Cross-level angle is positive when the right trunnions of guns or directors are depressed. 8.TRUNION TILT is the instantaneous inclination of the axis of the trunnions to the horizontal. 9. ROLL is the instantaneous value of the angle between the reference plane and the horizontal measured in the athwarthship plane normal to the reference plane. 10. PITCH is the instantaneous value of the angle between the reference plane and the horizontal, measured in a fore and aft plane normal to the reference plane. Note : For purpose of naval gunnery both roll and pitch are measured and recorded as rates; that is, in terms of amplitude per unit time, ordinarily as total degrees of roll (or pitch) per minute. 11. LINE OF SIGHT is the straight line joining the sight and the point of aim. 12. TRAGET ANGLE is the relative bearing of own ship from the target. measured in the horizontal plane from the bow of the target clockwise from 0° to 360°. 13. POSITION ANGLE is the vertical angle between the line of sight to an elevated target and the horizontal. 14. RELATIVE TARGET BEARING is the bearing of the target from the firing ship measured in the horizontal from the bow of the firing ship clockwise from 0° to 360°. 15. TRUE TARGET BEARING is the true compass bearing of the target from the firing ship. 16. GENERATED TARGET BEARING (relative or true) is the relative or true bearing of the target as determined mechanically or graphically from previous positions of own ship and target and established or estimated rates of change of bearing. 17. WIND DIRECTION is the compass direction FROM which the wind is blowing. 18. WIND ANGLE is the angle between the direction toward which the wind is blowing and the line of sights or projection of the line of sight in the horizontal. 19. TRUE WIND is the actual wind blowing unaffected by the motion of the observing station expressed as TRUE direction and TRUE speed (velocity). 20. APPARENT WIND is the wind apparent to the observing station and is the resultant of the true wind and the motion of the observing station- expressed as APPARENT direction and APPARENT speed (velocity). 21. BALLISTIC WIND is a weighted mean of the true winds at the various altitudes which the shell reaches in flight. 22. ALTITUDE is the height of an elevated target above the horizontal plane. It is ordinarily measured in feet. 23. DIP ANGLE is the vertical angle between the horizontal and the line of sight caused by (a) curvature of the earth, (b) difference in height between eye and object sighted upon. 24. VERTICAL PARALLAX is the vertical angle at the target formed by a line of sight from each of two stations (such as two guns, two directors, or a gun and a director) mounted at different heights on a ship. In surface fire it is equal to the difference between the two dip angles. 25. THE VERTICAL PARALLAX CORRECTION is the correction required to compensate the vertical parallax. 26. HORIZONTAL PARALLAX (CONVERGENCE) is the horizontal angle at the target formed by a line of two stations (such as two guns, two directors, or a gun and a director on a ship. 27. The HORIZONTAL PARALLAX CORRECTION is the correction required to compensate the horizontal parallax of the turret, or gun, from the gun director used as the origin in train for the system. 28. DIRECTOR CORRECTION is the vertical angle existing at the instant of firing between the director line of sight and the reference plane. If the director occupies a position above or below the reference plane an additional correction for vertical parallax is introduced automatically at the director. 29. BEARING RATE is the rate of change of bearing of target relative to own ship (relative movement of own ship and target at right angles to line of sight). It may be expressed in "knots" (linear measure) or in angular measure per unit of time, and is measured in the horizontal plane. 30. ELEVATION RATE is the rate of change of position angle. It has significance in antiaircraft fire only. 31. RANGE RATE is the rate of change of distance to the target (relative movement of own ship and target along the line of sight). In anti-air-craft fire control, the HORIZONTAL range rate is one component of the range rate. 32. FUZE SETTING is 'the instant measured on the fuse scale (zero of scale instant of discharge) at which the fuse is to function. In mechanical fuses this is the time of flight of the projectile. In powder fuses, the burning rate of the powder in the fuze train ordinarily requires a setting differing from the time of flight. FUZE SETTING is expressed in seconds, and fifth-second fractions, of time. 33. DEAD TIME is the total time elapsing from the instant of position (measuring range and bearing) the target until the gun is fired with data computed from that position. 34. TRANSMISSION INTERVAL is that part of dead time caused by lag in transmission of data. 35. SIGHT ANGLE is the vertical angle between the line of sight of a gun and the axis of the bore o£ the gun. 36. DIRECTOR SIGHT ANGLE is the vertical angle between the line of sight of a gun director (reduced to mean gun level) and the axis of the bore of the gun(s) controlled by the director. 37. GUN ANGLE is the angle between the reference plane and the axis of the bore of the gun. 38. A MIL is the unit of deflection and is the angle at the sight (gun or director) which subtends a horizontal distance at the target, at right angles to the line of sight, equal to 1/1,000 of the target distance. One mil is equivalent to 3.44' or 3'26" of arc. 39. TRUNNION T I LT CORRECTION IN TRAIN is the correction of the gun train order to compensate for the lateral errors due to the tilt of the trunnion, at the instant of firing. 40. TRUNNION TILT CORRECTION IN ELEVATION (vertical correction for trunnion tilt) is the correction to the gun elevation to compensate for the errors in range due to the tilt of the trunnions, at the instant of firing. 41. GUN TRAIN ORDER is the signal transmitted by the director (or from the director to associated instruments and as corrected by them) to the guns, indicating to the guns the correct position in azimuth in reference plane. 42. GUN ELEVATION ORDER is the signal transmitted by the director (or from the director to associated instruments and as corrected by them) to the guns, indicating the correct gun angle. RANGE 43. DISTANCE is the linear measurement between two points. 44. RANGE is the same as "distance" and in ordinary use is considered to mean the distance as determined by range finder, or other instrumental means, corrected for known errors. In analysis of gunnery performance the word "range" should not be used without a proper qualifying adjective or phrase. 45. RANGE-FINDER RANGE is the linear distance to a target as read from the rangefinder scale. 46. RANGE-FINDER CORRECTION is the correction to be applied to the range-finder range to correct for known (or estimated) errors. 47. CORRECTED RANGE-FINDER RANGE is the algebraic sum of the range-finder range and the range-finder correction. 48. MEAN RANGE-FINDER RANGE is the mean of the corrected range-finder ranges, taken simultaneously or approximately so, from two or more range finders. 49. MEAN RANGE-FINDER CORRECTION is the correction to be applied to the mean range-finder range to correct known or estimated errors of the range finders in use. 50. CORRECTED MEAN RANGE - FINDER RANGE is the means of the corrected rangefinder ranges of two or more range finders taken simultaneously or approximately so, or the mean range-finder range plus (or minus) the mean range-finder correction. 51. HORIZONTAL RANGE is the horizontal distance to a point directly beneath an elevated target distance multiplied by the cosine of the angle of position. 52. PRESENT RANGE is the best available estimate of the target distance. It is usually based on the corrected mean rangefinder range at the time of opening fire, but it may be based on the spotter's estimate of the target distance. It is continuously determined by the rangekeeper, or by plotting. 53. ADVANCE RANGE is the value of sight bar range computed by the rangekeeper, or by plotting. It is made up on present range combined with corrections for own ship and target movements during the dead time, and time of flight, other ballistic corrections, and "spots". 54. NAVIGATIONAL RANGE is the range or distance to the target from the firing vessel. It is determined after firing, from consideration of all available data. 55. GUN RANGE is the range in yards (shown in the latest range table in effect) corresponding to the angle of elevation above the line of sight to which a gun is laid when fired. It is equal to the sight bar range when the following circumstances apply : sight scales and range converters are graduated to the proper range table, there is no control ballistic and the point of aim is the desired point of impact, there is no uncorrected vertical parallax between gun and director, and erosion correctors are not used. 56. SIGHT BAR RANGE is the range in yards shown on the sight scale of the gun, the range converter or director, at the instant of firing. 57. HITTING GUN RANGE is the gun range that, if used would place the mean point of impact at the center of the target. It is equal to the gun range corrected for the error of the mean point of impact. 58. IMPACT RANGE is the distance from the firing point to the point of impact of the projectile. This can be accurately determined only at calibration practices. 59. BALLISTICS are computed corrections to be applied to the measured or estimated values of range and to the midpoint of the deflection scale to compensate for known or predicted errors and for variations from selected standard conditions. (a) GUN BALLISTIC consists of the corrections to compensate for the following variations from standard conditions: (1) Initial velocity errors due to temperature of powder and to gun erosion. (2) Errors due to atmospheric conditions of pressure temperature and wind. (3) Errors produced by relative movements of gun and target. (4) Errors caused by drift. (b) ARBITRARY BALLISTIC is a correction to compensate for the indeterminate errors in total ballistic used on previous firings, obtained by analysis of those firings. When used, this is combined with the gun ballistic in determining the gun range and deflection. A special arbitrary ballistic including correction for cold gun is often used for an opening salvo. (c) CONTROL BALLISTIC consists of the corrections to the gun range and deflection to obtain the sight bar range and deflection to compensate for the following: (1) In pointer fire... Point of aim correction. Sight scale range table correction. (2) In direct fire. Point of aim correction. Vertical parallax correction. Range converter-range table correction. (d) TOTAL BALLISTIC is the correction determined prior to firing to be applied to the present range and to the midpoint of the deflection scale to obtain the sight bar range and deflection. It includes the gun ballistic, arbitrary ballistic, and control ballistic. (e) INITIAL BALLISTIC is that portion of the total ballistic which is determined by computation (or graphs, etc.). It includes all elements of the total ballistic which are not determined mechanically and automatically, as by the rangekeeper, is in use, the INITIAL is the correction (range and deflection) applied manually to the rangekeeper just prior to opening fire. When no portion of the total ballistic is determined mechanically, the INITIAL BALLISTIC is equal to the TOTAL BALLISTIC. (f) BALLISTIC USED is the correction in range and deflection actually applied to the present range and to the midpoint of the deflection scale; in range it is equal to the difference between present range and advance range. For the opening salvo, the ballistic in use should be the same as total ballistic, if there are no errors in application. (g) HITTING RANGE BALLISTIC.HITTING PRESENT RANGE BALLISTIC is the correction in range which, if applied to the present range, will give the sight bar range (advance range) necessary to place the mean point of impact in range at the center of the target. HITTING NAVIGATIONAL RANGE BALLISTIC is the correction in range which, if applied to the navigational range, will give the sight bar range (advance range) necessary to place the mean point of impact in range at the center of the target. It can only be determined by past firing analysis. If this analysis shows that the present range was the same as the navigational range, then the hitting present range ballistic was the hitting navigational range ballistic. (h) HITTING DEFLECTION BALLISTIC is the correction in deflection, which, if applied to the midpoint of the deflection scale, would place the M. P. I. (in deflection) at the center of the target. 60. DRIFT ANGLE at any range is the angular lateral deviation due to rotation of a projectile in flight. 61. SUPER ELEVATION is the angle the gun must be elevated above targets, to compensate for curvature of the trajectory. 62. DEFLECTION is the lateral angular correction applied to the target bearing to obtain gun train order and thus offset the gun from the line of sight the proper amount to compensate for the lateral errors as computed or estimated. Sights and fire control instruments are designed for, and deflection is computed for, the application of deflection in the horizontal plane. However, unless corrected for trunnion tilt, the deflection is actually applied in the reference plane. 63. CORRECTED SIGHT DEFLECTIONThis term is frequently used when a separate instrument is used, to correct for the effect of trunnion tilt, and the value so designated indicates that it is the sight deflection corrected for the effect of trunnion tilt. 64. SIGHT DEPRESSION is the vertical angle the gun or director sights must be set below the gun bore (or gun pilot in case of director) to secure the gun elevation corresponding to the computed advance range, when the gun and director are elevated to bring the line of sight on the point of aim. 65. CORRECTED SIGHT DEPRESSION This term is frequently used when a separate instrument is used to correct for the effect of trunnion tilt and the value so designated indicates that it is the sight depression corrected for the offset of trunnion tilt in range. ARMAMENT 66. A CAPITAL SHIP is an armored vessel of war, not an aircraft carrier, mounting a battery of a caliber greater than 8 inches. 67. ARMAMENT of a ship includes all offensive weapons. 68. TURRET GUNS are all guns of 6 inches in caliber and larger mounted in a turret, or a mount. 69. BROADSIDE GUNS are guns of less than 6 inches in caliber, except antiaircraft guns and guns for saluting purposes only. 70. ANTIAIRCRAFT GUNS are intermediate caliber guns designed for use against aircraft. 71. DOUBLE PURPOSE GUNS are guns designed for use against both aircraft and surface targets. 72. ANTI-AIRCRAFT MACHINE GUNS are minor caliber fully automatic guns designed for use against aircraft. 73. MAIN BATTERY The term main battery includes those guns of the largest caliber on board. 74. SECONDARY BATTERY Only turret ships are considered to have a secondary battery; the secondary battery includes all except the turret guns and those guns specifically designated for use against aircraft. In ships having no broadside guns other than double purpose guns this battery may be designated as the secondary battery. 75. ANTI-AIRCRAFT BATTERY includes all anti-aircraft guns and anti-aircraft machine guns. 76. ANTI-AIRCRAFT MACHINE GUN BATTERY includes all anti-aircraft machine guns. SALVO ANALYSIS 77. A SALVO consists of two or more shots fired either simultaneously by means of a master key as in director or master-key firing, or on the same firing signal as in pointer fire. In gunnery exercises, a salvo is considered to have been fired when it is clearly the intent to fire two or more shots, but, through casualty, only one shot is fired. 78. The PATTERN of a salvo in range is the distance measured along the lone of fire between the shot of the salvo falling or bursting at the greatest distance from the firing point and the shot falling or busting at the shortest distance, excluding wild shots. In deflection it is the distance, measured at right angles to the line of fire, from the shot falling or bursting to the greatest distance to the left of the line of fire, excluding wild shots. 79. The MEAN POINT OF IMPACT is the point which is at the geometrical center of all the points of impact of the several shots of a salvo, excluding a wild shot. 80. The DISPERSION of a shot is the distance of the point of impact of that shot from the mean point of impact of the salvo. Dispersion in range is measured along the line of fire and in deflection at right angles to the line of fire. 81. The APPARENT MEAN DISPERSION of a salvo in range (or deflection) is the average of the dispersions in range (or deflection) of the several shots of the salvo, excluding wild shots. 82. The TRUE MEAN DISPERSION is obtained when an infinite number of shots are fired. The mean dispersion of a small number of shots. In analysis of gun practices, to obtain the true dispersion of a salvo the apparent mean dispersion of the salvo is multiplied by a factor depending upon the number of shots in the salvo, excluding wild shots. This factor represents the probable ratio of the mean dispersion of an infinite number of shots to the mean dispersion of that number of shots. 88. ERROR OF THE MEAN POINT OF IMPACT is the distance of the mean point of impact from the target or other reference point measured parallel to the line of fire for range and at right angles to the line of fire for deflection. 84. A STRADDLE is obtained for a salvo in range (or deflection) when, excluding wild shots and other shots of the salvo beyond the target (right and left, respectively, for deflection). 85. A WILD SHOT is a shot, the point of fall of which is abnormal as compared to the fall of the remainder of the salvo. For the purpose of the scoring and analysis of gunnery exercises, a wild shot is considered as a shot which fulfills one or both of the following conditions: (a) IN RANGE the shot must fall or detonate at a distance from the mean point of impact of the remaining shots in the salvo greater than 3.5 percent of the average gun range of the salvo for full and special velocity and greater than 4 percent of the average gun range of the salvo for target velocity. (b) IN DEFLECTION the shot must fall or detonate to an angular difference of more than 10 mils from the mean point of impact of the remaining shots in the salvo. 86. THE DANGER SPACE is the distance measured along the line of fire, in front of the target, such that, if the target were moved toward the firing point, a shot striking the base of the target in its original position would strike the top of the target in its new position. 87. THE HITTING SPACE for a material target is the distance behind the target that a shot striking the top of the target will strike the horizontal plane through the base of the target. Hitting space must be computed from column 19 of the range tables or directly from the angle of fall of the shot. Hitting space is the base for computing the limits of a constructive target when such is used for scoring hits in certain forms of gunnery exercises. Allowances are made for depth of the assumed target, in range, and in some cases, for an arbitrary distance short of the point of aim target. 88. LINE OF FIRE as used in analysis of gunfire is the true bearing of the target from the firing ship at the instant a shot (salvo) is fired. CONTROL 89. FIRE CONTROL comprises the entire system of directing the operation of the offensive weapons of a vessel, including necessary material, personnel, methods, communications and organization. 90. CENTRALIZED CONTROL is the control of a battery by the personnel of one control station. Sending out range, deflection, target bearing and director correction, ringing salvo signals; firing and spotting may be done at a station or stations other than the one controlling. 91. INDEPENDENT CONTROL is the control of a subdivision of a battery by the personnel of the subdivision. It includes the duties of control and the additional duties of computing and transmitting firing data, target bearing and director correction, ringing salvo signals, firing and spotting. 92. LOCAL CONTROL is the control of a gun or turret by the personnel of that gun or turret. It includes the duties of control computation and spotting of firing data, firing, and spotting. 93. A SPOT is the estimate made by the spotter, as a result of his observation of the fall of shot (bursts in the fire), to be applied to the gun range, deflection or fuse setting necessary to correct for the error of the mean point of impact (or burst) of a salvo. 94. SPOT APPLIED is the correction to the gun range, deflection or fuse setting actually applied as a result of a spot received. It may be the result of the co-ordination of several spots. 95. MATCHING POINTERS is the term applied to either "following the pointer" or "matching zero readers", in a fire control system in which an index (pointer or zero reader) on a local station instrument is kept matched with an index (pointer or zero reader) controlled from a distant station. METHODS OF FIRING 96. POINTER FIRE is the method of firing in which the gun sights are set for range and deflection and the pointing, training, and firing are performed locally at the gun. 97. MASTER KEY FIRE is a method of collective firing in which guns are trained and elevated in accordance with signals transmitted by a director or directors to the guns (or to associated instruments and as corrected by them to the guns) and then are fired from the director or directors. 98. DIRECTOR CORRECTION FIRE is that method of director fire wherein the guns are laid in elevation to an angle of elevation above the reference plane corrected for a pre-selected director correction and fired when the reference plane is inclined to the line of position by the pre-selected amount. 99. SELECTED LEVEL FIRE is that method of director fire wherein the guns are laid in elevation to the correct angle corresponding to a pre-selected level angle, and fired when the reference plane assumes that level angle. 100. SELECTED CROSS-LEVEL FIRE is that method of director fire wherein the guns are continuously aimed in elevation (to compensate for changing level angle) and are trained in accordance with a gun train order corrected for a pre-selected cross-level angle. The guns are then fired when the reference plane assumes this cross-level angle. 101. DIRECTOR FIRE IN TRAIN-ELEVATE BY TELESCOPE is that method of director fire in which the director transmits the gun train angle only and the gun is elevated as in pointer fire. 102. DIRECTOR FIRE IN ELEVATION-TRAIN BY TELESCOPE is that method of .director fire in which the director transmits the gun (elevation) angle and the guns are trained as in pointer fire. 103. INTERMITTENT CRANKING is the method of operating the director in which the director pointer follows the target with his elevating gear until near the point of reversal of the ship's motion, and then shortly after the reversal, fires when the horizontal cross-wire crosses the point of aim. 104. CONTINUOUS CRANKING OF CONTINUOUS AIM is the method of operating the director in which the director pointer attempts to keep the horizontal cross-wire constantly on the point of aim by means of his elevating gear. 105. INDIRECT FIRE is that method of director fire employed when the target is obscured to the firing station or when for other reasons the target is not used as the point of aim. In indirect fire a vessel or object whose position with reference to the target can be determined, may be used for determining the firing point in elevation, with a bearing generated by the rangekeeper or a computed true bearing by a navigational plot of the firing ship and target. 106. BARRAGE FIRE is a rapid fire using a fixed range, or fuze setting, so that the target, if it continues its course and speed, will pass through it. The barrage must be re-laid depending upon the movements of the target. A barrage is laid in a ZONE OF FIRE ; the area covered by the zone of fire is normally the pattern size of the group or battery of guns. 107. FIXED ZONE is a method of AA barrage fire by which the approaching plane is met by a series of zone barrages, or bursts of fire, all projectiles in each zone being fired with the same fuze setting and same sight angle. 108. CREEPING ZONE is a method similar to the fixed zone, except that in each zone the projectiles are fired with successively decreasing (or increasing) fuze setting. 109. ONE-MINUTE BARRAGE is the name given to a method of anti-aircraft fire in which a creeping zone is fired for a period of one minute prior to the time the bomber reaches the bombing point. FIRE DISTRIBUTION 110. DIVIDED FIRE: One ship firing at two or more targets. 111. CONCENTRATION: (a) Single fire: One ship firing alone at a single target. (b) Double concentration: Two ships firing at the same target. (c) Triple concentration: Three ships firing at the same target. (d) Quadruple concentration : Four ships firing at the same target. 112. A SPOTTING STATION is a location from which fall of shot (or brust) is observed; other functions of control may be exercised from the spotting station, but only when such other functions are definitely mentioned. 113. A PLOTTING STATION is a station for the determination of gun ranges and deflection, the reception and dissemination of fire control information, and for the possible control of fire. 114. A GUN DIRECTOR is an instrument for firing a battery or group of guns from a remote position, in accordance with the principles of director firing as set forth herein. 115. THE STABLE ELEMENT is a device for indicating the true horizontal plane, and for measuring the values of roll and pitch, or level and cross-level. It may be separately mounted or incorporated in a gun director | Text submitted by Pieter Bakels. | |
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