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APPENDIX D

COMMON MISTAKES AND MALPRACTICE


D-1. PROBLEM AREAS

Inaccuracies in cannon artillery fires cause wasted rounds and a decrease in the effectiveness of fire support. Many of these inaccuracies can be attributed to careless and/or improper procedures at the howitzer or aiming circle. The key to minimizing human error and careless gunnery procedures is proper training. The problem areas discussed below give the commander a starting point for evaluating the training level of his unit.

D-2. PRECUTTING CHARGES

Charges will be cut only after the command CHARGE is given or, if CHARGE is not announced, after a subsequent element of the fire commands (fuze, deflection, and quadrant) is announced. Often, when charges are precut, the increments are placed in a powder pit. This causes two problems, as follows:

a. The increments are exposed to moisture, direct sunlight, and so forth. Thus, it is impractical and unsafe to use them again.

b. If placed in a powder pit, the unused increments are normally burned before the unit leaves the position. If the fire missions involve the use of various numbered charge increments, there is a good chance that a wrong charge could be fired. If the propellent is not used and is missing one or more increments, it cannot be returned to the ASP because it is not a complete charge. A report of survey for accountability is required.

WARNING

Firing an incorrect charge is the single most common reason that a unit fires out of safety limits. This can result in fratricide. Do not place remaining powder increments for precut charges in the powder pit until the rounds for which the charges were cut are fired. For separate-loading ammunition, keep the remaining increments in the powder canister with the respective charge. For semifixed ammunition, dangle the remaining increments over the lip of each cartridge case and seat the projectile. However, do not break the cord until the round is handed to the number 1 man and the chief of section has verified the charge for each round.

D-3. LAYING ON THE WRONG AIMING POSTS

This mistake is especially possible at night. Howitzer sections can color-code their aiming posts to preclude this. This is an extremely important consideration if the unit is on a fire base.

D-4. IMPROPER EMPLACEMENT OF AIMING POINTS

a. Aiming points are emplaced at certain distances from the howitzer so that the proper sight picture may be established. This is especially important when one considers the matter of displacement. Displacement is the undesired movement of the sight caused by traversing the tube or by the shock of firing. That is to say, if the sight is not centered over the pivot point of the weapon or if the weapon shifts backward during firing, it will be oriented toward the aiming point from a different angle. Corrections for displacement must be made when using the two close-in aiming points (collimator and aiming posts).

(1) The primary aiming point is the collimator, which is normally emplaced 4 to 15 meters to the left or left front of the weapon. Displacement is corrected by matching the numbers in the pantel with the corresponding numbers in the collimator. If the collimator is not emplaced within the distance stated above, the three graduations visible in the collimator will not align properly; the picture will be out of focus. Therefore, it will be impossible to correct for displacement. If displacement is not corrected, the weapon will not be oriented in the direction of the target.

(2) The aiming posts are emplaced 100 meters (far post) and 50 meters (near post) from the pantel. If the far aiming post cannot be placed at 100 meters, the near aiming post should be placed half the distance to the far post (for example, far post, 90 meters; near post, 45 meters). This is very important for the following reasons:

(a) The distance to the aiming post is in direct relationship to the angular measurement taken when the displacement occurs. The farther the aiming post is from the sight, the smaller the angular measurement. The near post, because it is closer to the pantel, has the greatest angular measurement. This is the reason for the use of the near-far-line rule when correcting for displacement to the aiming posts. To correct for displacement to the aiming posts, the number of mils between the near post and the far post must equal the number of mils between the far post and the line (vertical line of the pantel).

(b) The rules of geometry and trigonometry tell us that if two points are on a line and the near point is half the distance of the far point from the origin, then the angle measured to the far point from a point that is not on the line is half the angle measured to the near point. That is to say, the angle measured to the near post will be twice that of the far post only if the near post is half the distance to the far post. Therefore, if the near post is not properly emplaced, displacement will not be properly accounted for, and the weapon will not be oriented correctly.

(3) To measure the distance from the piece to the aiming posts, the stadia method may be used. The pantel and the aiming posts are used as measuring devices.

(a) A cannoneer, in setting out the aiming posts, holds the upper section of one of the aiming posts in a horizontal position, perpendicular to the line of sighting. The gunner measures the length of the section in mils by using the reticle of the pantel. For example, the upper section of the aiming post is 4 ½ feet long and measures 14 mils when it is 100 meters from the piece (Figure D-1). The proper location of the near aiming post, in this case, would beat the point at which the 4 ½-foot section measures 28 mils (Figure D-2).

(b) In many cases, the ideal spacing of 50 and 100 meters cannot be obtained. However, the aiming posts are properly separated when the near aiming post is set at a point where the 4 ½-foot section measures twice the number of mils it measured at the far aiming post location. This measurement may be made at night by attaching the night lighting device at the 4 ½-foot marks on the aiming posts.

(4) Delay often occurs during emplacement of aiming posts when cannoneers move both the near and far aiming posts to achieve correct alignment. The procedure discussed below allows accurate placement of aiming posts in a minimum amount of time. Use of this method consistently results in posts requiring no more that 2 mils adjustment (often 0 mils), even when emplaced by entry level soldiers. This method, when used with aiming post lights, also greatly simplifies and speeds the night emplacement of aiming posts.

(a) Visually pick a point about 100 meters from the howitzer, and walk toward it in as straight a line as possible from the pantel. Place the near post in the ground 50 meters from the howitzer in as vertical a position as possible.

(b) Walk another 50 meters with the other post. Hold this post vertically in front of you. Looking toward the pantel, move the post left or right as directed by the gunner until the far post, near post, and the pantel of the howitzer are all on line.

(c) Ensuring the post is aligned with the gig line of your uniform, grasp the aiming post, raise your hands above your heat and stick the post vertically in the ground. The post should be vertical; adjust if necessary. Move to the near post and, with your right hand, adjust the post (if necessary) as indicated by the gunner.

(5) The DAP, though not emplaced, must be properly selected. When a single aiming point (other than the collimator) is used, it is not possible to correct for displacement. Therefore, the aiming point must be far enough from the pantel to ensure that there is no need to correct for displacement. The principle is very similar to that involving the aiming posts.

(a) The greater the distance between the sight and the aiming point, the smaller the angular measurement will be when displacement occurs. We do not normally fire deflections of less than 1 mil. Therefore, we must ensure that the angular measurement caused by displacement is less than 1 mil when we are using a DAP.

(b) We know that the greatest amount of displacement possible with any one weapon system is 1.5 meters. That being the case, we can determine the minimum distance for a DAP by using the mil relation formula.

b. It is important that aiming points are positioned and/or selected to ensure that the howitzer can be oriented for direction throughout the various transfer limits. As a minimum, the aiming point should allow the section to cover the primary, left, and right sectors.

Note: There are eight sectors of fire in a 6,400-mil circle. These sectors are derived from the theory of transfer limits (see paragraph D-5c below).

D-5. FAILURE TO COMPUTE TERRAIN GUN POSITION CORRECTIONS

a. The digital link between the BCS and the GDUs will at some point fail to function. The problem may be in the BCS, one or more of the GDUs, or the wire line. When the failure occurs, voice fire commands must be transmitted to one or more of the howitzers. If the failure is at the BCS, voice commands must be transmitted to each of the howitzers. Therefore, it is important that TGPCs be computed. These corrections, as a minimum, should be computed for the primary, left, and right sectors.

b. TGPCs provide acceptable effects within the transfer limits for which they are produced. TGPCs can be produced either manually or with the BCS or LCU. Presently there are two methods of producing TGPCs with BCS or LCU (see the applicable job aids for step-by-step procedures).

(1) Calculate data for the center of the transfer limit for all howitzers in the firing element (during peacetime, range to center of impact area; in wartime, center range for the particular charge). From the data derived, calculate the difference in time, deflection, and quadrant of one of the howitzers and the rest of the firing element.

(2) Using a converged sheaf, calculate data to the center of transfer limit for all howitzers and for a ghost gun, whose location is center of battery. Calculate the difference between the ghost gun data and those of the firing element. The ghost gun at battery center uses the average platoon or battery muzzle velocity. This method is not as desirable as that in (1) above because all howitzers must carry a TGPC.

c. Transfer limits are defined as an area 400 mils left and right of center and 2,000 meters over and short of the center range. TGPCs derived for a given transfer limit are effective as long as all weapons are within 200 meters of battery center.

d. Enemy attack capabilities may be so great and concealment so poor that the firing element must be spread over an abnormally large area. This may require that TGPCs be produced for two or more groups within the firing element individually. For example, if the howitzers are positioned about 250 meters apart, it would not be feasible to compute only one set of TGPCs for a given transfer limit. A solution to the problem would be to compute TGPCs for sections 1 and 2 and then for sections 3 and 4, both computations deriving corrections from separate group centers. The FDC could then transmit the two sets of data rather than four sets. This would speed up the delivery of fires and ensure that there would be effects on target.

Note: This consideration is extremely important when live fire exercises are conducted during peacetime training. When surface danger areas are computed, piece displacement factors are included. In general all weapons must be located within a 200-meter radius of a firing point marker or a surveyed grid location. Otherwise, an extended front must be requested. Consult local range regulations to determine restrictions of this type.

D-6. USING THE M139 OR M140 ALIGNMENT DEVICE TO VERIFY BORESIGHT

a. Boresighting is the process by which the optical axis of the weapons sights (the pantel and the elbow or direct fire telescope) are aligned parallel to the axis of the cannon tube. When this condition exists, the tube can be oriented parallel to the azimuth of tire upon occupation of a position. Thus, a target can be engaged with both indirect and direct fire.

b. When alignment devices were originally developed, it was intended that they be used to boresight. This was desirable because DAPs are not always available and transporting testing targets into a tactical environment is not practical. However, several problems have since surfaced which invalidate using an alignment device as a boresighting device:

  • Cross hairs in the alignment devices shift.
  • Locking lever wears and/or loosens.

c. Because of the above problems, the M139 or M140 should be used only to verify or check boresighting performed by other methods.

d. When performing fire control alignment tests, it is important that comparison tests be performed with the alignment devices to verify their accuracy.

D-7. OTHER MISTAKES

Other mistakes are as follows:

  • Failure to correct the gunner's aid when the corrections were not needed.
  • Transposition of numbers.
  • Failure to center pitch and cross-level bubbles.
  • Failure to compensate for backlash in the traversing handwheel by ensuring that the last movement of the handwheel is in the direction of the greatest resistance.

D-8. MALPRACTICE

Malpractice include blatant violations of standard procedures set forth in field manuals, technical manuals, and other publications. Some of these are as follows:

  • Failure to have a second, safety qualified person, orient the verification circle and verify the lay of the howitzers.
  • Having no system of double checks or leader checks on the actions taken.
  • Exceeding the maximum and/or sustained rates of fire.
  • Improper ramming, which may result in the projectile falling back on the propellent when the tube is elevated (separate-loading ammunition). If the projectile falls back on the propellant, expanding gases pass around the projectile (blow-by). This may decrease muzzle velocity. The projectile may be pushed forward towards the forcing cone. If so, the projectile will flutter and cause additional and unnecessary wear on the lands at the forcing cone.
  • Improper testing of the gunner's quadrant.
  • Improper or inconsistent placement of the propellant in the chamber.
  • Incomplete and/or improper fire control alignment tests. These tests must be conducted in accordance with the technical manual to ensure that the fire control equipment is synchronized with the cannon tube.
  • Cannon tubes improperly secured in travel lock. This causes damage to the traverse and elevation mechanisms.
  • Leaving projectiles and/or propellants exposed to direct sunlight for extended periods. The result is erratic firing.
  • Dropping projectiles or pallets of projectiles from the backs of ammunition trucks or carriers. Damage to the fuze well or rotating band may result.
  • Failure to clean dirty projectiles before loading. The result is increased resistance in the bore, and a dragging effect on the projectile during flight.
  • Lifting a round with a hand around the fuze.
  • Failure to use a fuze wrench when tightening fuzes. This increases the chance of an in-bore explosion if gases escape around the projectile, or it may bring about a low-order burst upon reaching the target area.
  • Removing the grommet protecting the rotating band before the round is placed in the bustle rack or on the loading tray.
  • Improper procedures when transferring from primary to alternate aiming points during a tire mission.
  • Attaching and/or picking up the lanyard before the proper command is given.
  • Standing in the path of recoil when priming or performing misfire procedures.
  • Failure to segregate propellent by lot.
  • Failure to perform prefire checks in each position.
  • Failure to cycle through the GDU on each command, verifying the number of rounds, charge, fuze, and projectile. Chiefs of section often look at only the deflection and quadrant.
  • Failure to cross-level the collimator.
  • Firing a round through an oily tube.
  • Moving an SP howitzer when there is no intercom communications between the track commander (TC) and the driver of the howitzer.
  • Improper shifting of trails on a towed howitzer. (Refer to -10 TM for that weapon system.)
  • Failure to perform equipment PMCS on a routine basis, especially cleaning the tube of the howitzer.

D-9. ERRORS IN SETTING UP AND ORIENTING THE AIMING CIRCLE

a. Some typical errors are as follows:

  • Failure to tighten the instrument-fixing screw securely. The head of the aiming circle will turn on the tripod, causing errors in readings given to the howitzers.
  • Not clearing the area of magnetic attractions (especially weapons, steel helmets, and eyeglasses) when the magnetic needle is used.
  • Failure to use a plumb bob and properly level the aiming circle, which could result in incorrect lay data.
  • Failing to first roughly orient the 0 -3,200 line when measuring an azimuth or an orienting angle. This could lead to a 3,200-mil error.
  • Inadvertently reading the red numbers rather than the black numbers on the azimuth scale.
  • Failure to set up the tripod so that one leg is oriented in the approximate direction of sighting. This puts one tripod leg in the instrument operator's way as he moves around and increases the likelihood he will knock the aiming circle off level or over.
  • Inadvertently moving the lower motion when movement of the upper motion is desired. When this occurs, the 0 -3,200 line will be reoriented along a different azimuth.
  • Making a 100-mil error in reading or setting deflections, instrument readings, and so forth on the upper motion. This is easy to do if one is not careful to read the numbers on the azimuth scale in a clockwise direction. When setting readings on the upper motion, it is best to set off 00 on the azimuth micrometer knob and then set off the first two digits of the reading on the azimuth scale.
  • Using an improper base length to perform subtense for distance measuring; for example, using the M16 when distance is greater than values listed in the appropriate table.
  • Failure to update piece location in the FDC with final lay deflections or when survey closes.
  • Verifying lay before the primary aiming point is emplaced or boresight is verified.
  • Leaving aiming circles attached to tripods during movement so they later become unserviceable.
  • Failure to verify the azimuth to the EOL. To verify the azimuth to the EOL--

- Set off the declination constant on the upper motion.

- Float and center the magnetic needle with the lower motion.

- Sight on the EOL with the upper motion, and check the reading on the scale with that given to the EOL.

- Map-spot the grid coordinates.

b. The result of an error in determining azimuth can be computed as it is a function of the mil relation formula. An error has a direct effect on direction and the accuracy of the fired round. See Figure D-3 and the example below.

D-10. INCIDENTS

Lack of attention to detail, improper supervision, and failure to make safety checks lead to mistakes and malpractices that cause equipment failure and injury or death to personnel. Some examples of incidents are discussed below.

a. During a live-fire exercise involving an M109A3 howitzer battery, unsafe charge data was transmitted from the BCS to the GDU. Both the FDC and the howitzer crew failed to catch the error. The round was fired out of safe, resulting in a fatal injury.

(1) The BCS operator and FDO failed to review the firing data before sending the commands to the firing battery.

(2) The howitzer crew failed to verify the firing commands against the safety T.

b. During a live-fire exercise involving an M109A3 howitzer battery, a howitzer misfired. The primer had fired, but there was no ignition of the propellant. The Number 1 crewman stated "It's just the primer; let me get it." As he stepped behind the breech, the cannon fired. The recoiling tube caught the Number 1 man in the chest and threw him to the rear of the cab. Also, fire from the breech recess engulfed the cab, burning several crewmen. The round fell short, just inside the buffer zone.

(1) The crew was not properly trained on misfire procedures.

(2) The Number 1 man had placed the charge in the powder chamber with the igniter forward, failing to announce I SEE RED! Therefore, the propellant was slow to bum until the igniter was lit. The M109-series weapons have breeches that open automatically when the tube is returned in battery. This resulted in tire escaping out of the breech recess.




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