# Indirect Fire - Mk6

## UNITS OF ANGULAR MEASUREMENT

Two major units of angular measurement the Army uses: milliradians (mils) and minutes of angle (MOA). Mils and MOAs describe a measurement of accuracy when firing a weapon, system, or munition. Mils and MOAs typically include the accuracy of a specific weapon, the performance of ammunition, and the ability of the fire as it relates to firing the weapon.

## MINUTE OF ANGLE

MOA is an angular unit of measurement equal to 1/60th of a degree (see figure below). The most common use of MOA is when describing the distance of change required when zeroing a weapon. One MOA equals 1.047 inches per 100 yards. For most applications, a Soldier can round this to 1 inch at 100 yards or 1.1 inches at 100 meters to simplify their arithmetic.

## MILs

The mil is a common unit of angular measurement that is used in direct fire and indirect fire applications.

A Mil is "the angle obtained by dividing one round of the circle by 6400". Usually, we use the 360-degree angle of 360

Use. However, the military measures the heading in a more accurate way to increase the accuracy of the fire and the accuracy of the location. Similarly for indirect fire from field and mortars,

Use this mill angle to aim for accurate shooting.

## Vector 21 Rangefinder

The Vector 21 rangefinder is an ACE3 added rangefinder. Unlike other rangefinders, it doesn’t just magically show you the range to your target, but in exchange allows you to do alot of things with it that the other choices in Arma do not offer. The Vector’s functions include, but are not limited to:

• Distance to a target

• Azimuth to a target

• Horizontal and vertical distance to a target

• Distance between 2 targets

• Angle between 2 targets

• Switching between feet and meters

• Switching between degrees and mils …

### Usage

The Vector is controlled with 2 keys: the azimuth key and the range key; Tab and Rand is brought up like any other binoculars.

### Distance

• Press and hold R until the red pointing circle appears. Sight the circle on the object and release the key.

### Azimuth

• Press and hold the Tab ↹ until the azimuth is displayed.

### Distance and Azimuth

• Press and hold both R and Tab ↹ until the red pointing circle appears.

• Sight the circle on the object and release both keys.

### Horizontal distance and height difference

• Tap R once then press and hold it until the red pointing circle appears.

• Sight the circle on the object and release the key.

### Azimuth and Inclination

• Tap Tab ↹ once then press and hold it until the azimuth and inclination is displayed.

### Distance between two points

• Press and hold R until the red pointing circle appears.

• Sight the circle on the first object and tap Tab ↹ while further holding R. The first measurement is confirmed (“1-P” = first point).

• Sight the second object and release R.

### Horizontal and vertical distance between two points

• Tap R once then press and hold it until the red pointing circle appears.

• Sight the circle on the object and tap Tab ↹ once. The first measurement is confirmed (“1-P” = first point).

• Sight the second object and release R.

### Horizontal distance and azimuth between two points

• Press and hold Tab ↹ until the azimuth appears.

• Sight the circle on the first object and tap R while further holding Tab ↹. The first measurement is confirmed (“1-P” = first point).

• Sight the second object and release Tab ↹.

### Fall of shot

• Tap Tab ↹ once then press and hold it until the azimuth appears.

• Sight the circle on the object and tap R while further holding Tab ↹. The first measurement is confirmed (“1-P” = first point).

• Sight the Fall of shot and release Tab ↹. The left digits display the left (L)/right (r) correction value in meter and the right digits display the longer (A = add)/shorter (d = drop) correction value in meter. If R is tapped the height correction values will be displayed (UP and down).

### Setting the measurement units (degrees/mils & meters/feet)

• Tap Tab ↹ five times fast. “Unit Set” appears briefly.

• Press R until the desired units are displayed.

• Tap Tab ↹ five times fast to save the selection.

## Kestrel 4500

The Kestrel 4500 Pocket Weather Tracker is Kestrel’s environmental meter. This is a mini weather station in itself:

• Wind direction

• Crosswind

• Altitude

• Barometric pressure

• Wet bulb temperature

• Relative humidity in %

• Dewpoint

• Density altitude

• Wind chill

• Temperature °C

• Time and date

• Minimum, Maximum and Average values

### Usage

• Open the self-interaction menu Ctrl + ⊞ Win

• Select Equipment

• Select Open Kestrel 4500

• User Screen 1: (m/s) - Meters per second

• User Screen 2: - Temperature

## Environment

ACE3 Weather extends the existing weather by temperature, humidity and air pressure according to the geographic location, season and time of day. It also ensures that all players experience the same weather effects.

## Wind info

• Wind info is toggled on/off using SHIFT + K.

• The arrow representing wind info is based on Beaufort scale

### Wind layers & wind strength

When it comes to wind in ACE3, there are many layers, to infinity and beyond. No matter how high you are, the wind will always be there with you.

Each layer has its own strength which depends on the actual weather around you and your current position. For the player, there are 3 things you will notice.

### Wind speed

Each of those arrows has a set of dots. First arrow has 1 dot, 2nd has 2, 3rd has 3, 4th has 4 dots and this can go on.

The more dots you see on the right side of the arrow, the color of the arrow will change.

The colors, as well as dots, show you the wind speed

### Wind direction

• When facing the target, a crosswind is a wind blowing left to right, or right to left

• When facing the target is the wind is blowing from front to back, it is a headwind

• When facing the target is the wind is blowing from back to front, it is a tailwind

Example:

------> 3 mph - 8 mph Wind coming from 10 o'clock to 4 o'clock (Blowing from left to right) (crosswind)

Now, think of the arrow as a clock. You have all of the directions displayed in the picture above.

Direction of the wind affects the bullet's trajectory.

Crosswind affects the bullet horizontally. Headwind and Tailwind affect the bullet vertically, the difference is in increasing the zeroing (Headwind) and decreasing the zeroing (Tailwind) regarding the bullet drop, but only after setting up the scope regarding the distance. Soon to be explained in the section after this one.

## Indirect Fire Theory

Indirect fire is aiming and firing a projectile without relying on a direct line of sight between the gun and its target, as in the case of direct fire. Aiming is performed by calculating azimuth and inclination, and may include correcting aim by observing the fall of shot and calculating new angles.

## Trajectory

The basics of external ballistics are simple, if a projectile is fired in a vacuum affected by gravity at some angle of elevation, then it will follow a parabolic trajectory to hit the ground. The constant curve is the result of gravity. However, the earth has an atmosphere so the projectile is slowed by air resistance. This significantly reduces the distance (or ‘range’) that the projectile travels before hitting the ground. For a rifle bullet the range loss may be as much as a factor of 20, for an artillery shell perhaps a factor of 3 or 4 depending on its caliber. Air resistance also means the trajectory fired at an elevation of less than 45° is no longer parabolic, but elliptic - a segment of an oval curve:

1. Its highest point (vertex) is no longer mid-way but closer to the target,

2. The angle of descent is steeper than the angle of departure, and

3. The impact velocity is less than the muzzle.

An implication of this oval segment trajectory is that, without any angle of sight, maximum range for any charge is given by an elevation angle of about 45°, however, 50% this elevation angle gives about 80% of maximum range. A shell loses velocity along its trajectory, although it gains a little in the final 10% or so of maximum range when the angle of descent steepens significantly and gravity makes a noticeable contribution.

Gravity also varies slightly and the total effect depends on and is a major determinant of the shell's time of flight because the total effect depends on the exposure time to the gravitational force.

## Coordinates

The two most basic pieces of information needed to calculate a firing solution (the angle you need to aim your artillery piece) are the coordinates of the artillery platform, and the coordinates of the target.

10 digit is preferred 8 digits will work if in a hurry

## Elevation

The elevation is the angle between the horizontal plane and the axial direction of the barrel of a gun, mortar or heavy artillery.

When an artillery piece is fired, it will only accurately hit the target if the target lies on the parabolic path of the round. This can be approximated without knowing the elevations, but accuracy will suffer greatly and need more information from spotters to correct for the error resulting from lacking elevation information.

## Air Resistance

Air behaves as a fluid, it is actually denser than water vapor, has higher viscosity than water or water vapor, and its viscosity changes with atmospheric conditions.

Arma 3 it is a deceleration that is applied uniformly to the shell

## Coriolis Effect and Eötvös Effect

The Coriolis effect causes Coriolis drift in a direction perpendicular to the Earth's axis; for most locations on Earth and firing directions, this deflection includes horizontal and vertical components. The deflection is to the right of the trajectory in the northern hemisphere, to the left in the southern hemisphere, upward for eastward shots, and downward for westward shots. The vertical Coriolis deflection is also known as the Eötvös effect. Coriolis drift is not an aerodynamic effect; it is a consequence of the rotation of the Earth.

You will notice that when you shoot north or south, your shots will start to "drift" right. This is because the earth (yes even in ARMA) is continuing to rotate beneath the shell, but the shell is not receiving the force from the earth. This means the ground is moving relative to the shell at a small speed.

Accounting for the Coriolis Effect stops your shells from drifting, but you still notice when you are firing the weapon. You notice that you tend to overshoot when shooting east, and undershoot when shooting west. This is known as the Eötvös Effect, and is caused again by relative motion to the ground. This time it is due to the apparent centrifugal force applied when moving in the same direction or against the earth's rotation. You must account for all three of these factors to begin zeroing a weapon.

## Angles

When solving for a parabola with two points, there are always two different solutions. The first is a "low angle" parabola that creates a more direct path toward the target. The second is a "high angle" parabola that stretches far into the sky before finally landing on the target.

The low angle results in a much faster delivery of the artillery payload, but may not be suitable if lots of hills, mountains, or large buildings are between you and the target. The accuracy can also be more variable with the low angle, as a small perturbation or deviation from the correct angle and direction will have a more drastic effect on the trajectory of the round.

The high angle will require more time to reach the target, but is likely to have less variability in accuracy and on average be more accurate. This is because small perturbations cause the rounds landing point to shift less.

## SHEAVES

A sheaf is the plane of fire of a group of weapons.

### Parallel Sheaf

Parallel sheaf occurs when you aim all the weapons in the battery the same direction and angle. Disregarding dispersion, the shells will land in the same pattern as the guns are set up. This is the easiest sheaf to do since all guns use the same firing orders.

### Regular Sheaf

Regular sheaf is when the shells are intended to land in a line with regular lateral spacing. This may, for instance, require the gun in the back of the battery to fire a little higher than the one in the front. This line usually runs perpendicular to the line between the guns and the target.

### Open Sheaf

Open sheaf is a regular sheaf where the spacing is chosen so the sheaf has maximum width (given the burst area of each shell) without any gaps in between. This spacing is somewhat smaller than the width of a single shell burst to accommodate a small amount of lateral dispersion.

### Converged (or Point) Sheaf

Converged (or point) sheaf occurs when all the guns are corrected to hit the same point. Also known as Precision Fire. Converged fire is called for to destroy a point target, a densely-packed target, or for point interdiction (such as on a bridge or crossroads).

## Setting up

To set up the Mk6 Mortar you must have both pieces with one of them being on the ground in front of you and one being in your backpack slot. Select the action: Assemble Mk6 Mortar.

• Place one of the packs on the ground

• While one pack is on your back, look at the other pack and select the assemble action.

• The mortar will be assembled facing the direction you were facing when you selected the assemble action.

Once assembled you can carry or drag the weapon by using ACE interaction. To tear down the mortar make sure you are out of it and select the action: Disassemble Mk6 Mortar.

## Sight

• Angle With Base – The difference angle between your rangefinder and the base of the mortar. Because elevation of the actual mortar is also measured from base this value needed for the ballistics computer.

• Optics Zoom – Self-explanatory. You can change it back and forth to max of 90.0x by using + and – keys on Num pad.

• Range – The range to the target in meters.

• Travel Time – Estimated time for the mortar round to reach the target.

• Vision Mode – There are 2 modes: normal, VIS and night vision NV, you don’t need to have NV Goggles.

• Actual Elevation – This is your mortar elevation that will directly influence the mortar travel arch, which will affect where it lands and its travel time. You change elevation the same way you change zeroing on rifles, Page Up and Page Down.

• Required Elevation – This is output of your ballistic computer based on range. Your Actual Elevation should be set to this value. If Actual Elevation < Required Elevation, the rounds will overshoot the target, if Actual Elevation > Required Elevation, they will fall short of target.

## Munitions

### High-Explosive (HE):

18-meter blast radius, has a penetration depth of 30 millimeters (direct impact only).

### Guided*:

8-meter blast radius, infrared-guided; will attempt to home into "hot" vehicles within a radius of 800 meters. The submunition separates from the main shell once it is 300 meters above the impact zone. The IR seeker has a 10% chance to lose lock against smoke countermeasures.

### Laser Guided (LG)*:

8-meter blast radius, laser-guided; can only lock onto laser spots within a radius of 800 meters. The submunition will "launch" from the dummy shell once it is 300 meters above the impact zone and begin seeking a laser spot.

• If no laser spot can be found, the shell will simply strike the point below where it separated from the primary shell.

## Ranges

It has three range modes available for firing:

• Close range: 34 to 499 meters (ETA 14-10 seconds)

• Medium range: 139 to 1,998 meters (ETA 28-20 seconds)

• Far range: 284 to 4,078 meters (ETA 40-29 seconds)

You need the proper mortar magazines in your inventory., or laying on the ground next to the mortar

• Interact with the mortar by pressing the interaction key ⊞ Win and looking near the muzzle.

• Select the Load Mortar action and then select the round type you want to load.

• If you want to unload the mortar without firing, interact near the muzzle again and select

Remove Round. If there isn’t space in your inventory for the round, it will be placed on the ground.

## FIRING PROCEDURE

### Locations

Get the distance and elevation difference between you and the target or the grid of the mortar, and the target grid

### Solution

What you need

• The location of the mortar

• The azimuth from the mortar to the target

• Wind speed and direction

• Temperature

Using my vector 21 linked to a micro dagr

Target

• Direction = 2533

• Range = 398m (call it 400)

• Elevation = 39msl

• Cross wind = 1.5mph left to right (D)

• Temp = 15c

Motar

• Elevation = 27msl

Solution

• Direction = 2534.35 (A)

• Tube Elevation = 1105.28 (B)

• Charge = 0

Tube direction math

• 2533 + 1.35 =2534.35 (D)

Tube elevation math (C)

• 1097 + ((69/100)*(39-27)) = 1105.28

• 1097 + (.69 * 12) = 1105.28

• Base +[the d elev / 100] * [elevation difference]

• To shift left direction -

• To shift right direction +

• To shift up, tube elevation -

• To shift down tube elevation +

Notes

If you are using a laser guided round the base from the range card will work

## Six elements of a call for fire

### Observer identification

Fire missions are started with the observer identification (call sign):

Mission type:

• Fire mission

### Target location

The grid of the target

### Target description

The target description should provide enough detail to enable the firer to determine the amount and type of ammunition to be used. The description should be brief, but accurate, and contain the:

• Type of target (troops, supply dump, trucks)

• Target activity (digging in, assembly area)

• Number of elements in the target (squad, three trucks)

• Degree of protection (in the open, in fighting holes, in bunkers with overhead cover)

### Method of engagement

Method of engagement describes the attack of the target. The options are “Danger close” and Munitions, if laser guided the laser code should be included.

For ARMA purposes Danger close ranges

• Under 200 meters, mortar

• Under 400 meters, Self-Propelled Howitzer

• Under 1000 meters, MLRS HE

• Under 2000 meters, MLRS Cluster

### At my command (AMC)

This announcement indicates that the observer desires to control the time of delivery of fire. The observer announces, "At my command," immediately preceding "Adjust fire or fire for effect."

### Cannot observe

This announcement indicates that the observer cannot adjust fire. However, the observer believes that a target exists at the given location, and the target is important enough to justify firing on it without adjustment.

### Time on target (TOT)

The observer may tell the FDC when he wants the rounds to impact by requesting, "Time on target (amount of minutes desired) minutes from now," or "Time on target zero six four five (0645) hours."

### Continuous illumination

If no interval is given by the observer, the section sergeant determines the interval by the burn time of the illuminating ammunition in use. If another interval is required, it is indicated in seconds.

### Cease fire

This command is used during firing of two or more rounds to stop the loading of rounds into the mortars. The gun sections may fire any rounds that have already been loaded (hung).

### Check fire

This command is used to cause an immediate halt in firing.

### Continuous fire

In mortars, this command means loading and firing as rapidly as possible, consistent with accuracy, within the prescribed rate of fire for the mortar being used. Firing continues until suspended by the commands CEASE LOADING or CHECK FIRE.