• 43. GENERAL.—The purpose of preliminary instruction with the gun is to train personnel to deliver prompt and accurate fire at the command of the gun commander and to train gun commanders to direct placing of quick and effective fire on a target. The final measure of the effectiveness of the gun in battle is its ability to destroy the targets assigned to it in a minimum of time. Before taking instructions in 37-mm gun marksmanship the soldier should be instructed thoroughly in the gun drill of the gun squad as described in chapter 2, and in stripping, mechanism, care, and cleaning of the gun as in chapter 1. He is then taught the mechan ical operations to be employed in firing the gun. He is taught these operations in their proper order and must be coached carefully. The instructional exercises to be taken prior to qualification tests are prescribed below. They are taken up in the order given and each man must be pro ficient in one exercise before proceeding to the next. If time is available, each exercise should be repeated a number of times for the purpose of increasing the soldier's proficiency in it. The progress made by each man in the exercises here inafter prescribed may be kept on record in the company on the progress chart shown below. During the instruction in duties of individuals in the service of the piece special emphasis is placed upon the necessity for accuracy. The soldier is made to understand thoroughly that speed is purely a matter of practice, but that accuracy can be obtained only by forming the habit of exactness from the beginning. Ra pidity is increased by insisting that each individual perform his duties in the prescribed sequence. • 44. DUTIES OF No. 2.—a. No. 2 is instructed that during firing he takes position on the right trail of the piece and assists the gunner by loading, firing, and unloading the piece. Before being instructed in the technical duties of the No. 1 (gunner) the soldier is taught to perform properly the duties of No. 2. b. No. 2 is taught to be on his right side with his hip resting on the right end of the trail brace and his right fore arm resting on the trail. In all drills and practice he is required to lie as close to the trail as possible so as to form the habit of doing so. By lying close to the trail he pre sents a small target and lessens the possibility of being observed by the enemy. c. To load the piece No. 2 is instructed to open the breech, grasp the cartridge by the rim with his left hand, insert the nose into the chamber, and push it in with the first two fin gers. He then closes the breech by placing the fingers of his left hand upon the breechblock lever and moving it to the right and down. The fingers do not grasp the breechblock lever but remain upon it until it meets the shoulder which limits the movement of closing. The fingers are then allowed to slide off the breechblock lever, thus preventing it from re bounding when it strikes the shoulder and insuring that the breech is fully closed. A simple demonstration will make it clear that the piece cannot be fired unless the breech is completely closed. An empty cartridge case fitted with a pointed wooden projectile or an empty cartridge case crimped in at the top can be used to advantage in training men to load and unload rapidly. d. No. 2 is taught to fire the piece by exerting steady pres sure upon the trigger with the thumb of his right hand, at the same time steadying himself by resting his right forearm and hand on the trail. As soon as the piece is fired his thumb is allowed to slide off the trigger. Unless this is done the trigger crank will intercept the forward movement of the sear arm in counterrecoil, causing the sear head to be de- pressed and thus preventing the automatic cocking of the piece. It should be impressed upon the soldier being trained as No. 2 that he fires the piece only at the command of the gunner. During the interval between rounds No. 2 keeps his thumb just above but not touching the trigger to prevent an accidental discharge which might result in injury to the gunner. As soon as the command to fire is given by the gun ner the piece will be fired immediately. Both No. 2 and the gunner remain steady on the trail and both remain motionless just before firing, as any movement at this time will decrease the accuracy of fire. e. To unload No. 2 is taught to open the breech with his left hand, placing his fingers under the breechblock lever and giving it a quick jerk upward and to the left with sufficient force to throw the empty case clear of the gun. His fingers do not grasp the breechblock lever because this would slow up the movement and might cause the gunner who has his eye to the sight to be struck in the head by No. 2's hand. • 45. DUTIES OF No. 1 (GUNNER) .—The gunner is instructed that during firing he takes position on the left trail and lays the piece in accordance with firing data received from the observer. In addition to being familiar with the details of laying for direct and indirect laying, the gunner should under stand the use and proper selection of aiming points, be able to determine the least range at which the piece may be fired and clear the mask, understand the practical methods of safely employing fire over friendly troops, and understand the proper manner of laying on a moving target on the ground. • 46. TRAINING OF No. 1 (GUNNER) ; POSITION AT GUN.—The gunner is taught to lie on his left side with his left hip resting on the left end of the trail brace and his left forearm resting on the trail. In laying the piece he grasps the elevating handwheel with his left hand and the traversing handwheel with his right hand. He keeps this hold when the piece is fired in order to maintain the proper laying and prevent undue dis placement from the shock of recoil. This precaution also re duces the time necessary to re-lay for direction and elevation. While the gunner is being trained to lay he is not at first required to hold his eye close to the sight during firing. By keeping his eye a few inches in rear of the sight at first the 48 37-MM GUN, M1916 46—47 gunner will be able to eliminate a natural tendency to flinch when the piece is fired, and with a little practice will become accustomed to remaining entirely motionless on the trail dur ing firing. A gunner who flinches is very apt to move the elevating and traversing handwheels and to jar the mount. The gunner soon becomes accustomed to the explosion and the recoil of the gun, and gradually learns to hold his eye nearer to the sight until he finally discovers that position for his eye which secures accuracy, speed, and safety. • 47. TRAINING IN DIRECT LAYING.—The telescopic sight is set for range and deflection in the manner described in para graph 21c. a. Sight-setting exercises.—In his first instruction in the setting of the telescopic sight the gunner is given the sight to hold in his hand. He sets off ranges and deflections com manded by the instructor who checks each setting before commanding the next. The sight is then placed on the gun and further practice is given the gunner in setting off range and deflection. b. Aiming with telescopic sight.—Accurate shooting cannot be done unless the cross lines are laid on exactly the same point for all shots. The better defined this aiming point is the easier it is for the gunner to relay on the same point. Dur ing a soldier's first instruction in aiming he is taught to aim at clearly defined points. To this end a small paster about 2 inches square is placed on a screen about 25 yards in front of the gun. The instructor lays the gun by aiming at the paster. In aiming at the paster the intersection of the cross lines is laid upon one corner of the paster in such a manner that two sides of the paster coincide with the cross lines in one quadrant of the field of the telescope. The instructor explains that either quadrant may be used for the first laying and points out the necessity for placing the paster in the same quadrant of the field of the telescope in all subsequent laying on the same aiming point. The gunner is then re quired to aim at this point several times, the instructor check ing the aim each time. When the soldier has become pro ficient in aiming at pasters he is taught to aim at stakes, posts, poles, and larger objects. In aiming at such objects the cross lines are placed so that the vertical line coincides 49 47 37-MM GUN, M1916 with one edge of the object and the horizontal line coincides with the top, bottom, or some distinguishable mark on the object. The soldier is taught next to aim at natural targets such as small bushes, light and dark colored patches on the ground, and small features of the terrain that are readily distinguishable. In aiming at such targets the soldier must be impressed with the importance of selecting for his aiming point that part of the target on which he can most easily and quickly re-lay the cross lines after fire is opened. The gunner therefore should place the cross lines upon the most clearly defined part of the target whether it is the top, bottom, center, or side (fig. 11). c. Aiming exercise.— (1) The equipment required for this exercise includes the following: (a) 37-mm gun mounted on tripod with the telescopic sight in place. (b) Target frame, 3x5 feet, covered with blank paper. (c) Marking disk, 8-inch. (2) The target frame listed above is the 1,000-inch ma chine-gun target issued by the Ordnance Department. The marking disk is 8 inches in diameter. It is made of tin or cardboard, painted black, and is mounted on a white wooden handle approximately 3 feet long. A hole is punched in the center of the disk just large enough to admit the point of a pencil. (3) The exercise is conducted as follows: The gun is mounted on the tripod with the telescopic sight in place. A target frame covered with blank paper is placed 100 yards from the gun and the cross lines of the sight are laid on the blank target. The pupil takes the gunner's position and looks through the sights without disturbing the aim. An assistant designated as "marker" stands in rear of the target and places the marking disk on the blank target holding it firmly in position against the paper. By command or im provised signal, the pupil directs the marker to move the disk until it is in correct alinement with the cross lines of the sight (see circular object, fig. 11) and then commands: MARK. The marker without moving the disk makes a dot on the paper with a sharp pointed pencil inserted through the hole in the center of the disk. The marker then moves the disk to change the alinement. The pupil without disturbing the orig- 50 37-MM GUN, M1916 47 inal aim repeats this operation until three dots numbered 1, 2, and 3, respectively, have been made. These dots out line the shot group and the pupil's name is written under it. The size and shape of the shot group is discussed and the errors pointed out. This exercise is repeated until pro ficiency is obtained.. The pupil should be able to make a shot group that can be covered by a %-inch circle. d. Using an aiming point other than target.—When the gunner has been trained to use the target as an aiming point, he is next taught how to use an aiming point other than the target when the target does not offer a suitable aiming point. This method is described in paragraph 83. To im press the gunner with the necessity and importance of using a clearly denned aiming point instead of laying upon an indistinct target, he is required to lay upon an indistinct target, throw the line of aim off, and relay upon the target several times. This exercise will illustrate the difficulty of picking up an indistinct target. The instructor also em phasizes the fact that the smoke and dust caused by burst ing shells make the target even more indistinct. After the reason for using an aiming point other than the target has been illustrated the gunner is taught that he can quickly lay the gun to hit the target by aiming at any well-defined point near the target. The first step is to lay the intersec tion of the cross lines upon the target with zero deflection and the range to the target set on the sight. Then by turn ing the deflection and range dials the intersection of the cross lines is moved to the selected aiming point and the gunner then calls out the new range setting on the sight. The gunner is given exceptionally thorough instruction in this method because it is frequently used in combat. Having been shown the necessity for using such an aiming point and in structed in the mechanical method of using one, the gunner is given practice in the selection of aiming points for various indistinct targets pointed out by the instructor. • 48. TRAINING IN INDIRECT LAYING.—a. Sight-setting exer cises.—The gunner is trained how to set off range, deflection, and angle of site with the quadrant sight in a manner de scribed in paragraph 22c. The gunner is instructed to set the quadrant sight by the methods of instruction described in paragraph 47a. b. Laying for direction with quadrant sight.— (1) When the quadrant sight is used for indirect laying, the gun is laid for direction but not for elevation by alining the vertical line in the quadrant sight upon some aiming point in the same manner as the vertical cross line in the telescopic sight is alined (fig. 11). 52 37-MM GUN, M1916 48 (2) The gunner is instructed first in laying the vertical line of the collimator upon the simplest form of aiming point as, for instance, a vertical stake about 25 yards in front of the gun. The instructor first lays the gun and then re quires the gunner to look through the sight. The gunner is then required to lay on the stake, repeating the operation several times until proficient. In laying upon such an aiming point one edge of the stake is used. (3) The gunner is next taught to use other aiming points which present a vertical line upon which the vertical line of the collimator can be laid. Such aiming points are houses, poles, and trunks of trees. In using a house as an aiming point the edges of the chimney, sides of the windows, or the corners of the house are used in the same manner as the edge of a stake. (4) The gunner is shown that deflection can be uniformly measured from any point on a vertical line, but that deflec tion measured from different points on an inclined line will vary. The gunner therefore is trained to pick out vertical lines as aiming points for direction and to lay the vertical line of the collimator upon them. The instructor checks the gunner's aim to see that he has selected a proper aiming point and that he has laid accurately upon it. (5) It will often happen that aiming points which present vertical lines upon which to lay the vertical line of the sight cannot be found. For this reason the gunner is taught next to lay the vertical line upon a point. To do this the gunner lays on the aiming point by placing the vertical line of the collimator on the aiming point. Aiming points used in this instruction should at first be small pasters placed on a screen in front of the gun. When the gunner has become proficient in laying on a paster he is given practice in laying upon small natural objects. (6) The next step in training the gunner to lay for direc tion by means of the quadrant sight is to practice him in selecting and laying upon aiming points on large objects such as buildings, trees, and bushes. He is called upon to select that point on such an object which makes the best point upon which to lay the vertical line of the collimator. The instructor checks the gunner's aim to see that he has 53 48 37-MM GUN, M1916 selected the most clearly denned point upon which to lay and that he has laid accurately upon it. (7) The gunner is now taught how to provide a suitable aiming point for use in maintaining direction when the piece has been previously laid for direction. In teaching this method the instructor lays the piece for direction and tells the gunner that the piece is laid in the proper direction to hit the target but that the sight is not alined upon any aiming point. He then tells the gunner to aline the sight upon some aiming point which may be used to maintain the direction of the piece during firing. The gunner then selects a suitable aiming point, preferably a well-defined natural ob ject on the ground to the front, and alines the vertical line of the collimator upon it by means of the range and deflection dials. He does not move the traversing handwheel during this operation as doing so will move the gun barrel from the proper direction to hit the target. Should the gunner not be able to find a suitable aiming point on the ground within the limits of movement of the deflection dials, he places a stake or other object in such position that it can be used as an aiming point. An ammunition box, a stone, or a piece of paper or cloth weighted down can be used. The gunner directs the placing of this aiming point a short dis tance in front of the gun in such position that the vertical line of the collimator can be brought upon it without chang ing the direction of the barrel. The gunner then alines the vertical line upon this aiming point as before by means of the range and deflection dials. In the firing of successive rounds the gunner relays for direction each time by alining the vertical line on the aiming point by means of the travers ing handwheel. c. Laying for elevation.—When the gunner has been taught to lay the piece for direction he is taught to lay the piece for elevation. The instructor announces the angle of site and range to be set off on the sight by the gunner. The in structor explains that the setting off of the angle of site and range does not move the axis of the bore, and that the next and last step in laying the gun for elevation is to center the bubble by means of the elevating handwheel. The in structor drills the gunner in laying the gun for elevation for 54 37-MM GUN, M1916 48 different angles of site and ranges until he is found to be proficient. d. Determination of minimum range.—This operation is a mechanical one and the gunner will be made proficient in performing the operation before any attempt is made to ex plain to him the reasons for the various steps. The gun is set up behind a crest or behind any artificial object which may simulate a crest. The gunner is told that he can deter mine the least range at which he can fire over the crest from a given gun position with a given angle of site by the follow ing steps: (1) Set off the range to the crest on the range dial with the angle-of-site dial set at zero. (2) Lay the gun by turning the elevating screw handwheel so that the horizontal cross line in the collimator just clears the top of the mask. (3) Center the bubble by means of the range dial. (4) Set off the angle of site of the target on the angle-ofsite dial and read the minimum range on the range dial oppo site the index on the angle-of-site dial, and announce the minimum range to the gun commander. The gunner is drilled in performing these four steps which comprise the operation of determining the minimum range until they become me chanical with him. This operation is quite different from laying the piece in indirect laying, yet the beginner will often confuse the two. For this reason the gunner will not be given instruction in determining the minimum range until he is thoroughly familiar with the methods of laying the piece. When the gunner has become proficient in the method of determining the minimum range, he is made to understand thoroughly its application in firing. He must realize that the minimum range is the least range which he can set off on the range dial and fire over a mask from a certain gun position as long as he uses the same angle of site on the angle-of-site dial as he used in determining the minimum range. He must also realize that when the gun commander announces a new angle of site or when the gun is moved to a new position he (the gunner) must find the new minimum range. He will also be taught to announce to the gun commander the minimum range immediately after it is 55 48-50 37-MM GUN, M1916 found. He will further be instructed that he is to notify the gun commander when a range less than the minimum range is announced in a fire order. When the gunner has a thorough understanding of the above method he may be taught how to find the minimum range by the shortest method for the same gun position for a new angle of site. This method consists of setting off the angle of site used in first determining the minimum range on the angle-of-site dial, setting off the minimum range first found on the range dial opposite the index on the angle-of-site dial, then without moving the range dial, setting off the new angle of site and reading the new minimum range on the range dial oppo site the index on the angle-of-site dial. • 49. EXECUTION OF FIRE ORDERS.—After the gunner has been taught to lay the gun properly for direct laying, he is drilled in executing fire orders such as those described in paragraph 100 until he can lay the gun with speed and accuracy. Men are taught to execute fire orders for indirect laying in a like manner. • 50. DUTIES OP OBSERVER.—a. It is the duty of the observer to direct the gun squad in placing prompt and effective fire upon a target. He obtains the firing data for the first shot for the purpose of placing the first shot upon the target or as near to it as possible in a minimum time. During the firing he observes each burst and gives to the gunner the corrections in deflection and range necessary to bring the fire upon the target. The observer keeps himself informed of the position of friendly troops and when fire is to be delivered over their heads he is responsible that no firing is ordered which en dangers them. When range cards are necessary he prepares them for the positions of his gun. b. During firing the observer maintains a position from which he can see the target and be in communication with the crew at the gun. When direct laying is employed his position is at or near the gun, and his orders are given to the gunner by voice. In indirect laying when it is necessary for the observer to be at a short distance from the gun in order to see the target, he uses the simplest and most direct method of communicating with the gun crew. This method is by 56 37-MM GUN, M1916 50-51 voice direct to the gunner. The next best methods are by visual signals or by voice, with a man stationed between the observer and gun repeating the fire orders. If it is not possible to use either of these methods, communication is maintained by runner or by mechanical means such as the buzzer or telephone. The essential rule is that the more sim ple and direct the means of communication, the more prompt and effective will be the fire, and that if communication be tween observer and gun is interrupted the weapon becomes useless. « 51 TRAINING OF OBSERVER; DIRECT LAYING.—a. General.— When a soldier has been found proficient in the duties of gunner he is instructed in the duties of observer. The first step in training the observer is the method of obtaining the firing data for direct laying. It is here that training in the estimation of ranges is given. Instruction in target desig nation is also given for the purpose of enabling the observer to give to the gunner the firing data which have been found. b. Training in preparation o/ range cards.—Range cards are prepared as described in paragraph 119. The men are divided into squads under noncommissioned officers and taken to suitable terrain. The officer in charge explains to the men the method of preparing range cards, requiring the men to perform each step of the work as he describes it. Noncom missioned officers supervise the work of their squads, pointing out any mistakes and requiring the men to correct such mis takes before proceeding with their work. The men are then required to prepare a range card of the same terrain with out help from the instructor. The instructor collects these cards, points out any mistakes in them, and requires the men to correct these mistakes. This operation is repeated until the men are considered proficient. c. Determination of ranges.—In combat the exact range required to hit a target will seldom be known prior to the opening of fire, and a material saving of time and ammuni tion will be effected by accurate range estimation. If fire is opened with an incorrect sight setting the position of the gun is often disclosed before fire falls on the target, thus increasing the probability of casualties in the gun crew, am- 57 51 37-MM GUN, M1916 munition is wasted, and overhead fire may be rendered unsafe. (1) Methods of determining ranges.—The usual method of range determination used with the gun in combat is estima tion by eye. Other means may be used but the main reli ance must be placed on estimation by eye. Range finders are bulky, require trained observers, and must be kept in accurate adjustment. Measurement on the ground is prac ticable only in specially prepared defensive positions and in the absence of the enemy. Accurate maps are good but re quire more time than is usually available. Ranges may be secured from other troops, particularly when making a relief. (2) Necessity for training.— (a) As estimation by eye must be depended upon in combat all men, and especially gun com manders, should be trained in this method. Stress should be laid on estimating ranges between 600 and 1,400 yards. (b) The estimation by eye of untrained men is little better than a guess and the average errors of such men will be at least 12 percent of the range. A definite system of range estimation frequently practiced is the only way to make esti mation by eye sufficiently reliable. (3) Method of estimation by eye.— (a) Estimation by eye consists of measuring the range by applying to it a unit of measure 100 yards long. The method is the same as that employed in measuring the length of a board with a ruler. The only difference is that the soldier's unit of measure is applied mentally. Thorough familiarity with the 100-yard unit and its appearance on different kinds of ground and at different distances will enable the estimator to apply it with a fair degree of accuracy. (b) Knowledge of terrain, life in the open, and training in scouting and patrolling are helpful in range estimation. (c) Application of the unit of measure beyond 500 yards is difficult. For this reason in ranges over 500 yards it is better to select a point halfway to the target, apply the 100-yard unit up to this halfway point, and multiply the estimated dis tance by two. (d) The average of a number of estimates by different men will generally be more accurate than a single estimate. How ever, in combat the gun commander must usually rely on his own estimation. 58 37-MM GUN, M1916 51 (4) Conditions affecting appearance of objects.—(a) Con ditions of light and terrain have considerable effect upon the appearance of objects making them seem sometimes much nearer and at other times much more distant than they really are. The effect of these conditions on the appearance of the 100-yard unit of measure is negligible. (b) In some cases much of the ground between the observer and the target will be hidden from view and the application of the unit of measure to the hidden portion of the ground will be impossible. In such cases the appearance of objects is the only guide. (c) If there is a considerable stretch of visible ground ex tending from the far edge of the depression to the target it is best to estimate the distance to the far edge of the depres sion, judging by the appearance of objects, and then to apply the unit of measure over the remaining distance to the target. (d) Whenever the appearance of objects is used as a basis for range estimation the observer must make allowance for the effects noted below: 1. Objects seem nearer when— (a) Object is in a bright light. (b) Color of the object contrasts sharply with the color of the background. (c) Looking over water, snow, or uniform sur face like a wheat field. (d) Looking from a height downward. (e) In the clear atmosphere of high altitudes. (f) Looking over a depression, most of which is hidden. 2. Objects seem more distant when— (a) Looking over a depression, all of which is visible. (b) There is a poor light or fog. (c) Only a small part of the object can be seen. (d) Looking from low ground toward higher ground. (5) Exercises.—(a) No. 1. 1. Purpose.—To familiarize the student with the unit of measure, 100 yards. 59 51 37-MM GUN, M1916 2. Method.—The unit of measure, 100 yards, is pre viously staked out over varied ground, using markers that will be visible up to 500 yards. The men are required to become thoroughly familiar with the appearance of the unit of measure from prone, kneeling, and standing positions at various ranges. They do this by moving away from and in prolongation of the lines staked out and studying the appearance of the unit from distances of 100, 200, 300, and 400 yards, (b) No. 2. 1. Purpose.—To illustrate the application of the unit of measure. 2. Method.—Ranges up to 900 yards are measured accurately and marked at every 100 yards by large markers or target frames, each bearing a number to indicate its range. Men undergoing instruction are then placed about 25 yards to one side of the prolonged line of markers and directed to place a card, hat, or some other object before their eyes so as to cover from view all of the markers. They are then directed to apply the unit of measure five times along a straight line in the general direction but slightly to one side of the markers. When they have selected the final point reached by mentally ap plying the unit to the ground five times, the eye cover is removed and the estimations of the successive 100-yard points and the final point are checked against the markers. Ac curacy is gained by repeating the exercise. 3. Ranges greater than 500 yards are then considered. With the markers concealed from view in the same manner as explained in 2 above, men esti mate the ranges to points which are obviously over 500 yards distant and a little to one side of the line of markers. As soon as they have announced each range they remove their eye covers and check the range to the target and to 60 37-MM GUN, M1916 51 the halfway point by means of the markers. Prone, sitting or kneeling, and standing posi tions are used during this exercise, (c) No. 3. 1. Purpose.—To give practice in range estimation. 2. Method.—From a suitable point ranges are previously measured to objects within 1,000 yards. The instructor conducts the class to the point where the men are required to estimate the ranges to the various objects that are pointed out by the instructor, writing their estimates upon paper previously issued. At least one-half of the esti mates are made from prone or sitting positions. Thirty seconds are allowed for each estimate. When all ranges have been estimated, the papers are collected and the true ranges an nounced to the class. Individual estimates and squad averages are posted on bulletin boards accessible to all members of the class. d. Field-glass and range-table method.—The observers are taught how to obtain the firing data necessary in indirect laying when an aiming point other than the target is used by means of the field-glass and range-table method. To do this the observers are trained in measuring angles with the horizontal and vertical mil scales in the type EE field glass. The instructor draws a rough diagram of the horizontal and vertical mil scales as they appear in the field glasses and gives a brief explanation of their use. He then stations the observers with field glasses about 25 yards from a blank white panel or the side of a building. He makes two marks of the same height on the panel and requires each observer to measure the horizontal angle between the two points. He checks their readings with his field glass or by use of the mil formula, since he knows the distance from the observers to the target and the distance between the two marks. The instructor then makes two marks on the panel, one above the other and requires the observers to read the vertical angle between the two points. This is checked in the same manner as the horizontal angle. Care must be taken that the men use the mil scale in reading the vertical angle rather than 216513°—40———5 61 51-52 37-MM GUN, M1916 the inverted sight leaf which is found in the field glasses. The observers are then instructed in the use of the angle-ofdeparture table in the determination of the range to be used when laying upon an aiming point above or below the target. This method is described in paragraph 83b. The instructor may give preliminary instruction in the use of this method by making two marks (one to represent the aiming point, the other to represent the target) on the panel which vary both in direction and elevation. He gives the observers an as sumed range to the target as represented by one mark and requires each observer to compute the firing data necessary to use the aiming point represented by the other mark. • 52. INDIRECT LAYING; METHODS OP OBTAINING DIRECTION.— a. General.—The various methods of obtaining the direction for indirect laying are described in paragraph 86. The observer is first taught the simplest and most commonly used methods. Later he may take up the more difficult methods. To comprehend the methods of obtaining direction by com pass the observer is given training in the use of the lensatic compass, modified prismatic type, as prescribed in paragraph 19. The observer is given, considerable practice in the use of compass, both in reading and setting off magnetic azimuths, before he can be considered proficient. b. Determination of angle of site.—The first step in train ing an observer to determine the angle of site is to teach him to determine the horizontal. This is done indoors or on level ground which may be found adjoining the barracks. The instructor requires each observer receiving instruction to place a mark on the wall at the height of his eye. Each observer stands facing his mark on the wall at a distance of 10 yards or more if possible. He raises his extended arm, wrist straight, palm down, fingers extended and joined, until tips of the fingers are the same height as the mark on the wall. The tips of the fingers then indicate the level of the observer's eye. The observer repeats this step several times. He then practices locating the level of his eye without the mark which is covered by another man until the observer has located what he believes to be the level of his eye. After repeating this operation several times and checking each time by means of the mark, the observer is ready to proceed to the 62 37-MM GUN, M1916 52-54 next step. He is then taken to a position affording a good view of the terrain and is required to indicate different points on the ground to the front which he believes have the same elevation as his position. The elevations of these points are checked by the instructor using an angle-of-site instrument. When the observer has been given a few trials in the selection of these points and has shown a fair degree of accuracy in them, the method of obtaining the angle of site described in paragraph 88 is explained to the observer and he is practiced in using it. Only a few minutes' daily practice for several days is necessary to train an observer to estimate the angle of site with sufficient accuracy. If no angle-of-site instrument or other instrument designed for measuring angles of site is available, the point on the ground in front or in rear of the target having the same elevation as the gun position is found by means of the quadrant sight on the gun as follows: Set angle-of-site dial and range dial at zero and center bubble by means of elevating handwheel. The horizontal cross line is then laid upon all points in the field of sight having the same elevation as the gun position. This method can be used by the instructor in training ob servers to estimate the angle of site but cannot be used in action. The angle-of-site instrument is not issued to the gun commander for use in the field, the estimation of the angle of site by a trained observer being sufficiently accurate for the firing of the first round. Use of the angle-of-site instrument is confined to the training of the observer. • 53. FIRE CONTROL; FIRE ORDERS.—The observer is trained in giving fire orders (see par. 100) while other men are being trained in the duties of gunner. The fire order must be given in the prescribed sequence in order to avoid errors on the part of the gunner, and the different parts must be given at sufficient intervals to enable the gunner to set off the data on the sight as they are given. The observer will require the gunner to repeat the fire order correctly, step by step, as it is given. • 54. TRAINING IN ADJUSTMENT OF FIRE.—a. The best and most direct method of teaching the observer to conduct fire is by practice firing. However, ammunition allowances re- 63 54 37-MM GUN, M1916 strict the use of this method and it will be necessary for the instructor to devise other means. Training in adjustment of fire may be given in the classroom and a suitable method of teaching this subject is described in b below, b. (1) Articles of equipment required are— Blackboard. Sand table. Burst pointer. Any desired terrain may be reproduced on the sand table as described in paragraph 153. The burst pointer is a class room pointer split at one end with a small ball of cotton about l/2 inch in diameter placed securely in the split end to represent the "burst." (2) The instructor first explains the method of sensing described in paragraph 103 and the method of correcting the errors thus sensed by means of fire commands. To illustrate this explanation he uses a blackboard to show a sketch of the line gun-target and a second line perpendicular to it through the target. He plots the bursts and explains their deviation from these lines as described in paragraph 103. The group to be instructed is then assembled at the sand table where exercises similar to those described in c below are conducted. (3) The equipment is set up with the gun placed approxi mately 1,000 inches from the general area of the targets. The observation point may be at the gun position or to the flank, depending on, the exercise. The observer uses the mil scale in the field glass, type EE, to measure deflection errors on the miniature terrain. Ranges are indicated by placing markers in depth along an edge of the sand table. Cards about 3 by 4 inches numbered to indicate ranges in hundreds of yards (10, 11, 12, etc.) are suitable markers. c. Exercises.—(1) No. 1 (direct laying).—The instructor designates a target which is also the aiming point. The observer computes the initial firing data for engaging the target and gives the fire order. During the early stages of instruction the observer may pattern his fire order after a model on a blackboard near his position. When the observer has given his order, the instructor (standing alongside the sand table) says "On the way," and momentarily places the 64 37-MM GUN, M1916 54 tip of the burst pointer at a point on the range approximately where the fire order would cause the shot to strike. The observer estimates the errors in deflection and range and issues a flre order to correct them. This procedure is con tinued until the required final bracket is obtained. Example.—The instructor designates a target that is also to serve as aiming point on the sand table at a range of 1,000; the observer gives the fire order "Low explosive, 1,100, zero, that stump, one round." The instructor places his pointer beyond the target; the observer sees that the burst is an "over" and issues the fire order "900, one round." The instructor places his pointer before and to the right of the target (to bring out a deflection change); the observer esti mates the error in deflection with his field glasses, sees that the burst is a "short" and issues the fire order "1,000, left 10, one round." The instructor places his pointer in front or in rear of or hits the target, depending on the point he desires to bring out. Should the observer give an incorrect fire order such as right deflection instead of left deflection, the instructor places the burst as called for in order to em phasize the error by demonstration. (2) No. 2 (direct laying).—The instructor places his pointer on an aiming point other than the target and points out the observation post. The observer computes the initial firing data for engaging the target. The actual vertical and hori zontal differences in mils between the target and aiming point as measured with the field glasses on the sand table are used for calculating initial firing data. The observer issues the flre order and the instructor places the bursts until the prob lem is completed as in (1) above. (3) No. 3 (indirect laying).—Before the exercise the in structor has two or three aiming stakes set up a few feet in front of the gun position, and a contour outlined on the miniature range and arbitrarily assumed to be on level with the gun so as to give a zero angle of site. The instructor designates a target and points out the observation post. The observer computes the initial firing data by measuring the horizontal difference in mils between the target and the aim ing stake, the vertical difference in mils between the "zero angle-of-site contour" and the target for the plus or minus 65 54-56 37-MM GUN, M1916 angle of site, and by estimating the range. The observer issues the fire order and the instructor places the bursts until the problem is completed as in (1) above. (4) Other exercises.—When the observer has progressed sufficiently he works out more difficult problems to bring out the necessity of remembering where bursts at certain ranges appeared; the necessity of constant study of the terrain so as to recognize when bursts are "lost over" a hill, "lost short" in a ravine in front of a target, "lost in a woods on a flank," and the like; the necessity of studying wind conditions as when a cross wind causes the smoke to go across in front of or behind a target; correcting a shot in deflection only as when the burst appears to be correct as to range but off the line from gun to target, and determining whether the shot is an "over," a "short," or a "target" at that range when on the line gun-target; and the necessity of making correc tions for the difference between the observed error in deflec tion and the actual deflection to be set off on the sights, depending on the position of the observer in front, rear, or flank of the gun.
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