artillery

Sheafs

Now let's turn away from single-gun considerations and turn to battery fire. A sheaf is the planes of fire of a group of weapons. Depending on how the weapons in the group are aimed, the pattern formed by the group may take several forms.
Parallel Sheaf Regular Sheaf Open Sheaf Converged Sheaf

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.

Light and medium artillery usually use parallel sheaf. This may also apply to British heavy artillery. [2]

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 type of 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 accomodate a small amount of lateral dispersion. Heavy artillery usually uses open sheaf!

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).

Unusual Sheafs

The normal shape for a sheaf is a line perpendicular to the line-of-fire. Specially-shaped sheafs can be arranged unders certain circumstances, such as strangely-shaped targets, point targets, barrages, etc, but this would be the exception. Individual gun corrections for normal sheafs can be handled by the battery itself; for special sheafs, the calculations are done at the Fire Direction Center.

Preplanned barrages, which would be planned well before the start of an operation, would be more flexible in this respect in that there is plenty of time to do all the complex computations.



The Sheaf/Volley Tables

The following interesting table is taken mostly from the US manual, with some of the time numbers being derived from ROF numbers elsewhere. The first table is the statistics for a single battery of size 4 or 6 guns, with open or converged sheaf. Volleys is the number of volleys necessary to suppress troops in the area of impact, while rounds is simply Volleys times Battery Size. "Initial" gives the rate-of-fire during the first four minutes, when the guns are preloaded for the first volley, and time shows how long the guns would have to fire to put the "Rounds" figure in the air. The "Sustained" column shows longer-term fire, the ROF is greatly decreased due to ammo handling and gun cooling considerations.

Single-Battery Table

Weapon Battery
Size
Sheaf Area
W×D
(yards)
Volleys Rounds Initial Sustained
ROF Time ROF Time
75mm Howitzer 4 Converged 50×100 5 20 24 0:50 10 2:00
Open 120×100 12 48 24 2:00 10 4:48
6 Converged 50×100 3 18 36 0:30 15 1:12
Open 130×130 8 48 36 1:30 15 3:12
105mm Howitzer 4 Converged 75×100 3 12 16 0:45 6.6 1:49
Open 150×100 6 24 16 1:30 6.6 3:38
6 Converged 75×100 2 12 24 0:30 10 1:12
Open 200×130 6 36 24 1:30 10 4:48
155mm Howitzer 4 Converged 100×100 3 12 8 1:30 2.7 4:30
Open 250×100 8 32 8 4:00 2.7 12:00
6 Converged 100×100 2 12 12 1:00 4 3:00
Open 300×130 6 36 12 3:00 4 8:00
155mm Gun 4 Converged 100×150 5 20 8 2:30 4 5:00
Open 250×150 11 44 8 5:30 4 11:00
8" Howitzer 4 Converged 150×100 3 12 6 2:00 2 6:00
Open 380×100 7 28 6 4:40 2 14:00
8" Gun 2 Converged 120×150 6 12 3 4:00 1.3 9:00
Open 230×150 12 24 3 8:00 1.3 18:00
240mm Howitzer 2 Converged 130×150 6 12 3 4:00 1.3 9:00
Open 250×150 10 20 3 6:40 1.3 15:00



Battalion Fire Table

Range Spread 0 Range Spread 1/2 Range Spread 1

When an entire battalion fires, the batteries can choose to put all their sheafs on the same point, or to spread their sheafs downrange so there is some or zero overlap. The following table shows the statistics for various weapons with three batteries each of four or six guns in several arrangements:

Weapon Pieces Sheaf Range
Spread
Area Volleys Rounds
75mm Howitzer 12 Converged 100×150 4 48
Open 0 150×200 8 96
½ 150×250 9 108
1 150×300 12 144
18 Converged 100×150 3 54
Open 0 150×200 6 108
½ 150×250 6 108
1 150×300 8 144
105mm Howitzer 12 Converged 150×150 3 36
Open 0 200×200 5 60
½ 200×250 6 72
1 200×350 9 108
18 Converged 150×150 2 36
Open 0 250×200 4 72
½ 250×250 5 90
1 250×350 7 126
155mm Howitzer 12 Converged 160×150 2 24
Open 0 300×200 5 60
½ 300×250 6 72
1 300×350 9 108
18 Converged 160×150 2 36
Open 0 350×200 4 72
½ 350×250 5 90
1 350×350 7 126
155mm Gun 12 Converged 160×200 3 36
Open 0 300×250 6 72
½ 300×300 8 96
1 300×400 10 120
8" Howitzer 12 Converged 200×150 2 24
Open 0 400×200 5 60
½ 400×250 6 72
1 400×350 9 108



Multi-Battalion Fire Table

If multiple battalions attack a target, the effect and beaten zone is larger. The smaller areas on the following table are if careful correction is done:

BattalionsWeaponBattery SizeArea
2 105mm Howitzer 4 200×250 to 250×300
6 300×250 to 350×300
2 155mm Howitzer 4 250×250 to 300×300
6 350×250 to 400×300
3 Mixed   350×300 to 400×400




Other Observed Fires

Direct Laying

Direct laying is the term for direct fire, when the target can be seen from the piece. Self-observation is used.

Assault Fire

When attacking a strongpoint or bunker, pinpoint fire from 2500-4000 yards can be used. Fine control of the fire is obtained by using more trial fires and possible aiming boards to get 1/4 mil deflection.

High-angle Fire

Fire at an angle greater than the elevation that produces maximum range (say, 45-50º) is high-angle fire.

Mortars effectively always use high-angle fire, and guns cannot be elevated enough for high-angle fire -- only howitzers can do both low and high-angle fire.

HE (fragmentation) shells are improved in effect when the angle of impact is high, because all the side-spray fragments are travelling parallel to the ground in a 360-degree circle, while in low-angle fire half the shrapnel is expended harmlessly in the air. Ricochet fire is not possible. Dispersion is higher than low-angle fire, since the shell is in the air much longer, so unobserved high-angle fire is avoided.

Some weapons have "gaps" for high-angle fire no combination of elevation and charge will cause the round to fall correctly. High-angle fire with delay fuze may be useful in penetrating thick jungle foliage or canopy.

High-angle fire with quick fuse is about twice as effective against personnel standing or walking in the open. [2]

Barrages

A barrage is a prearranged barrier of fire designated to protect friendly troops and installations by impeding enemy movements across defensive lines or areas.

Each battery is laid on its barrage when not otherwise occupied and fires on barrage signal or call from the supported unit. The most effective barrages are the width of an open sheaf, though wider areas can be covered by shifting the entire battery or by spreading the batter and moving each gun in small increments. Unlike normal fire, barrages can easily be at any angle relative to the line-of-fire.

Target Marking

Artillery is sometimes used to identify targets for ground-attack aircraft, using colored smoke. Coordination must be arranged well in advance of the striking crafts' arrival on the battlefield.

Counterbattery

Flash, sound, radar ranging, or direct observation can be used to pinpoint enemy artillery. US Radar was good only against enemy mortars and could only give rough map positions, so they were generally treated as targets of opportunity. Division and corps assets were used more often in the counterbattery role, either as part of a prearranged fire plan or as a heavy concentration of surprise fire on enemy mortars.

A battalion would be used for the initial neutralization, followed by a battery or two just to maintain it. WP and HE, in about a 1:4 ratio, were an effective combination.

Time-on-Target (TOT) Fire

TOT fire is a technique when the volleys from several units arrive on the target at the same time, for maximal surprise. Of course, it takes time to calculate the flight time and coordinate all the units, so this type of attack will be longer in setting up.




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