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CHAPTER 8

SPECIAL SITUATIONS


8-1. DIRECT FIRE

Direct fire is a special technique that demands a high standard of training and requires the section to operate as an independent unit. It should be used only as a last resort. Considerations for direct fire engagements are discussed below.

a. Trajectory. Trajectory characteristics change with the range to target and charge fired. The following information is based on use of charge 7.

Note: To produce the highest muzzle velocity and a flat trajectory, the maximum charge should always be used for direct fire.

(1) 0 to 400 meters. This is the most accurate range at which to engage a target with direct fire during combat, because the trajectory is flattest.

(2) 400 to 1,500 meters. In this zone, the trajectory is . flat enough to allow direct estimation of range without actual bracketing of the target. Range changes in 50-meter increments give the best results.

(3) 1,500 to 2,500 meters. Hits are only reasonably possible in this zone. The bracket method of adjusting will probably be required to obtain a hit.

(4) Over 2,500 meters. Direct fire is not effective.

b. Types of Targets. The most likely direct-fire targets are vehicles and/or dismounted personnel. Vehicles are engaged as point targets. Personnel are engaged as area targets. Direct-fire priorities should be as follows:

    • Vehicles at short ranges threatening to overrun the position.
    • Stationary vehicles covering the advance of other vehicles.
    • Command and control vehicles.

c. Ammunition

(1) Shell/fuze combination used against armor and vehicular targets are as follows:

    • 105mm--Shell high explosive plastic-tracer (HEP-T); shell HE with impact, mechanical time, or variable time fuzes set for superquick action; and shell WP with impact or mechanical time fuze set for superquick action.
    • 155mm--shell HE with impact, mechanical time, or variable time set for superquick action and shell WP with impact or mechanical time fuze set for superquick action.

Note: WP projectiles can be used effectively to ignite immobilized vehicles. Smoke and WP projectiles can be used to obstruct the vision of vehicle drivers and tank gunners and serve to disorient them.

(2) Shell/fuze combinations used against personnel are as follows:

    • 105mm--antipersonnel (APERS-T) and shell HE with impact (set for delay action), mechanical time, or variable time fuzes (set for superquick action) fuze.
    • 155mm--shell HE with impact (set for delay action), mechanical time or variable time fuzes (set for superquick action) fuze.

Note: When used against personnel, shell HE with impact fuze (delay action) is fired at a point 10 to 30 meters in front of the target to achieve the best effects.

8-2. DIRECT FIRE SIGHTING METHODS

The three primary methods of sighting used in direct fire are as follows:

a. Two-Man, Two-Sight. This method is best for all weapons except the 105-mm howitzer M119. The gunner establishes lead with the pantel, and the AG establishes elevation with the direct fire telescope. This is the fastest and most accurate method of sighting. It permits the AG to check the direction of lead. The reticle in the direct-fire telescope must be level. A canted reticle in the direct fire telescope will prevent satisfactory direct fire on moving targets because an unacceptable range error is introduced when lead is changed.

b. Two-Man, One-Sight. The gunner establishes lead with the pantel, and the assistant gunner sets elevation on the elevation quadrant at the command of the chief of section. This method is not effective when the target is moving on other than flat terrain.

c. One-Man, One-Sight. This method is least desirable and should not be used unless absolutely necessary. The gunner lays for lead and elevation with the reticle of the pantel. This method should not be used if the target is moving or on a steep slope.

8-3. DIRECT FIRE LAYING METHODS

The two primary methods of laying for direct fire are discussed below.

a. Reticle Laying. The gunner maintains lead by placing the vertical hairline the proper number of mils ahead of the point of aim on the target (Figure 8-1).

b. Central Laying. The gunner sets the lead in mils on the azimuth micrometer scale of the pantel and maintains the vertical hairline of the reticle on the center of the target (Figure 8-2). There is a modification on the knob of the M100-series pantel called a click sight. It permits the gunner to set off lead in 5-mil increments, by sound or feel, without removing his eye from the sight.

8-4. COMMANDS FOR DIRECT FIRE

a. The platoon leader/XO or BC will direct the engagement of targets by certain sections using verbal commands. Normally, individual section commands for direct fire are given by the howitzer section chief. The commands include the following:

  • A warning order--TARGET (so-and-so).
  • General direction to the target--LEFT FRONT.
  • Lead in mils (how to determine lead is explained in the weapon manual)--LEAD, RIGHT 5.
  • Range to target--RANGE 800.
  • Method of fire--FIRE AT WILL.

b. The shell, fuze, and charge to be fired should be standardized to save time. If a shell-fuze combination other than the standard is desired, the command SHELL (so-and-so), with time (if applicable), is given after the direction to target.

c. The howitzer section chief gives subsequent commands based on the observed effects.

(1) Change in lead. During adjustment, the lead in mils is changed to a new total lead command.

EXAMPLE

The initial fire command was LEAD LEFT 5. After spotting the burst, the section chief decides a lead of 10 will hit the target. His subsequent command is LEAD LEFT 10.

(2) Change in range. During adjustment, the range is increased by the command ADD (so many meters) and is decreased by the command DROP (so many meters). Another option is that the section chief announces a new range based on the desired increase or decrease in range to hit the target. Unit SOPs will dictate which technique to use.

d. When commands for direct fire are issued, firing battery personnel must ensure that direct-fire engagements do not result in fratricide. This is the particular responsibility of the howitzer crew, section chief, FDO, platoon leaders, and platoon sergeants in a platoon-based unit and of the XO, chief of tiring battery, and GSG in a battery-based unit. (See AR 385-63 on minimum engagement ranges.)

8-5. EMERGENCY BORESIGHTING

a. Boresighting is the only means a gunner has of ensuring that the optical axis of his sights are parallel to the tube of the weapon. The weapon should be boresighted in the following cases:

  • Anytime the sight has been subjected to any shock other than tiring.
  • Before firing in a new firing position (verify).
  • Anytime the howitzer fires inaccurately for no apparent reason.

b. The primary methods of boresighting are:

  • Distant aiming point.
  • Test target.
  • Standard angle.

c. When time is not critical and the tactical situation permits, use of the test target may be preferred over the DAP method because of its accuracy.

d. Boresighting methods are discussed in detail in the applicable weapon manuals. The following paragraphs describe several boresighting techniques that may be used if, for some reason, one of the primary methods is not possible.

8-6. COLLIMATOR METHOD OF BORESIGHTING

The collimator may be used to boresight weapons. Procedures are as follows:

a. Prepare the weapon for boresighting in the same manner as for the DAP method.

b. Place the collimator about 20 feet in front of the tube.

c. Sight through the tube and align the 0 of the collimator with the vertical muzzle boresight string.

d. With the pantel, sight on the collimator and match the numbers on the reticle pattern of the sight with the numbers on the collimator. The reading should be as follows:

  • 3200 on the azimuth scale of the M 100-series sight.
  • 0 on the slip scale of the M12-series sight.

Note: This method may not work with the M109A3/A6 or M198 howitzers. Because of the length of the tubes on these howitzers, the numbers in the collimator may not be visible during the alignment portion (paragraph c above) of the boresighting process.

8-7. STANDARD ANGLE METHOD OF BORESIGHTING

For the M101A1, the standard angle must be established during the conduct of a fire control alignment test. The procedures are outlined in the applicable weapon manuals. To boresight by the standard angle method, do the following:

a. Establish the recoiling parts in the same relationship to the nonrecoiling parts as they were when the standard angle was established.

b. Place a pin in the left witness mark on the muzzle.

c. Install the parallax shield.

d. Set the standard deflection angle on the telescope.

e. Using a tested gunner's quadrant, set the standard elevation angle.

f. Match all standard angle scribe lines.

g. If the weapon is out of boresight, do not disturb the bubbles. Adjust the vertical hairline onto the junction of the pin and the muzzle.

Note: As soon as possible, the boresight should be verified by a more accurate means.

8-8. AIMING CIRCLE METHOD OF BORESIGHTING

a. Set up the aiming circle approximately 30 to 50 meters in front of the weapon (Figure 8-3).

b. Insert the boresight disks and strings in the cannon.

c. With the upper motion of the aiming circle, set off 0000 (for M12-series sights) or 3200 (M100-series sights).

d. Align the cannon bore on the aiming circle, and center the cross-level bubble of the pantel.

e. With the lower motion of the aiming circle, align the vertical hairline on the center of the cannon bore.

f. With the upper motion of the aiming circle, align the vertical hairline on the pantel of the weapon. Read the instrument reading (angle from center bore to pantel) to the weapon.

g. The gunner sets the announced reading on the pantel. He then adjusts the pantel by using the tangent screws, or the boresight adjustment shaft, until his sight picture is centered on the lens of the aiming circle.




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