Updated 6 June 2014

A brief introduction to indirect fire and mobile firepower

For about the first six centuries of its existence artillery was limited to direct fire.  The cannon was pointed directly at a target that its gunners could see.  The required amount of gunpowder was loaded and some adjustment was made to the vertical angle of the barrel.  The gunners observed the impact of their cannon ball (not always easy due to the smoke) and adjusted their aim for their next shot.  In essence, this sort of procedure continued until the German invention of the 'richt-fläche' in the early 1890's.  Over the following 20 years or so artillery became an indirect fire system and direct fire was only used in exceptional circumstances or by infantry and assault guns.  This wasn't entirely accepted by the 'old guard' in most European armies but 1914 quickly demonstrated its reality.

In English the 'richt-fläche' translated as 'lining plane' but became the 'goniometer' and then when optics were added the 'dial sight' (UK) or 'panoramic telescope' (US).  It enabled a gun to be aimed without its target being visible from the gun position, which meant that each individual gun no longer selected its own target.  The original intent of indirect fire was probably to allow guns to engage targets to their immediate front from behind the cover of a local crest.  This made them invisible to enemy artillery, machine guns and long range rifle fire.  Some not very effective methods for this had been devised in the years before 1890's and there is some evidence that the Russians used such methods in the early 19th Century.  Interestingly, before 1914 there was very little thought given to the problem of acquiring these concealed guns as targets and how these targets might be attacked.

However, the effect of indirect fire was that any target that was within range of a gun could be attacked by it, by day or night whatever the weather, providing there was a means of acquiring it.  This also meant that all guns within range of a target could attack it.  The means for mobile firepower had been created, where the guns of many batteries could be concentrated on one target and then a minute or so later attack another many miles away in a different direction without having to move as direct fire weapons did.

Of course making the most effective use of indirect fire meant that a system had to be created, although 'evolved' might be a better term.  Apart from efficient communications equipment, most of this was done in World War 1, coming to fruition in 1918.  The main components of this mobile firepower system are described on the following pages:

Fire could be ranged or predicted, ranged meant that an observer or target acquisition system in the air or on the ground had to correct the fall of shot.  Predicted  fire (originally called 'map shooting') required accurately knowing the target's map coordinates.  Additional data was needed ensure accurate fire, this had two aspects, the actual local conditions and the data to convert these into corrections to firing data.  Firstly there was meteorological data: air temperature, air pressure, wind speed and direction, which had to be determined and distributed to each battery every few hours.  Secondly the guns have to be periodically calibrated to determine their current muzzle velocity.  Depending on how fast they wear and how much they fire this could be anything from a few days to a few months.  This all adds further complexity to the system.

In addition the various artillery units have to be suitably organised and equipped with vehicles, fire control instruments and other necessities (see 'Artillery Organisations' page), and it all requires very substantial logistic support stretching back to the ammunition factories.  Underpinning the entire system are well-developed procedures, effective and efficient communications (see 'Artillery Communications' and 'Fire Discipline' pages) and well-trained soldiers including various specialists.  'Royal Artillery Methods in World War 2' page ties all these elements together.

In essence targets fall into one of two categories, the unforeseen ones engaged as impromptu targets and planned targets.  The basic system for impromptu targets is shown below, most usually they were originated by an artillery observer with the combat troops.  These observers were usually the troop commanders, nominally captains, in field and medium batteries.  Sometimes battery commanders (majors) and occasionally more senior officers engaged impromptu target.  From mid-war they were joined by the pilots of air observation Austers, who were all artillery officers despite the aircraft being RAF, see the 'Other Firepower' page.

The Basic System

iArtillery system schematic

The second category were planned targets.  These could be planned where the enemy might be or appear.  They were engaged according to a plan of engagement, a 'fireplan', with scheduled or 'on-call' targets.  Such plans were used to support an attack, a defence, an advance to contact or other type of operation.  They were typically planned by artillery staffs at divisional or corps HQs, although as the war progressed planning also occurred at lower levels.  Targets could be engaged with concentrations where all guns were aimed at the area around a point or barrages where fire was aimed at long lines with fire shifting from one line to the next in the case of moving barrages.

Planned targets were typically engaged with maximum accuracy because once firing started ranging was not usually acceptable.  An opportunity target, as illustrated in the Basic System diagram above, was used against targets that had not been planned and fire was usually ranged.  A significant development in the middle of the war was the UK development of procedures that enabled the massed fire of many batteries against an impromptu target, including by observers who had the control authority to give the orders without reference to an artillery commander, see the 'Concentrations of Massed Fire' page.  

For large fireplans batteries could be positioned in suitable areas, but against impromptu targets batteries fired from wherever they were.  Therefore to maximise massed fire guns need good range and the ability to cover a wide arc of fire.

All the components of the artillery system have to be combined in an effective and efficient system, and this does not necessarily mean having the best guns or best target acquisition or best anything else (whatever 'best' means!).  None of these components in isolation or aggregation is the same as having an effective (does the right thing) and efficient (does the thing right) system.  Furthermore, in efficient armies this artillery system does not exist in isolation, it is properly integrated with the other fighting elements on the battlefield.  

The key features of an effective artillery system are the capability to:

Indirect fire requires clear differentiation of command and control.  Command of artillery concerns the allocation of resources, primarily firing units (batteries, battalions, brigades) and ammunition.  Control is the allotment of firepower against particular targets.  In an effective artillery system batteries do not have to be transferred between commanders for their firepower to be available to them.   This meant that while the British divisional artillery was commanded by the divisional commander it could also be allotted to another, while non-divisional artillery was commanded at a high level and allocated as appropriate,  usually according to a standard 'scale', and again allotted as required.

The basic building block of artillery is the battery with between 2 and 8 guns, which the British sub-divided into sections of 2 and troops of 4 guns.  Batteries are organised into battalion sized units of 2 - 4 batteries, regiments in British terminology.  Batteries have their own observers who deploy in observation posts with good observation over an area or with infantry and armoured units to acquire and engage targets.  There are also specialist target acquisition batteries and air reconnaissance provides a further capability.

Target acquirers may either order or request fire against a target.  Requests always go through a fire control HQ that allots guns to engage the target.  The techniques of gunnery and its control procedures enable targets to be efficiently attacked with controlled indirect fire.  A defining feature of the British artillery system is that target acquirers routinely order fire to the guns, in contrast to the US system where they always request fire.  This is neither a trivial nor a semantic distinction, and is reflected in organisation and tactics.  The British system devolves control to the lowest practical level by allowing the observers to give orders to the guns.

Some armies, including the British, regard the shells fired by the guns, not the guns themselves, as their actual weapons - the things that provide firepower.  Indirect fire means mobile firepower, to fully exploit its potential two things are involved:  

The second sounds simple but in WW2 it was never achieved by the Red Army, who adopted a cruder approach of physically massing lots of guns where they thought they were needed.  Even in the US Army theory did not always work in practice because of 'proprietorial' attitudes by some commanders - they fixated on the principle of 'unity of command' (which the British did not recognise) and didn't understand 'control' as applied to artillery.

To get maximum benefit from a system that delivers massed mobile firepower the extent of the area that each battery can influence is important.  This is the combination of range and arc of fire.  The first seems straightforward, basically it's an innate characteristic of the gun and ammunition combination, but is not clear-cut.  The second is more complicated involving the gun, local terrain and time.

Figures for range have to be treated with caution.  Range can increase or decrease by hundreds of yards depending on the 'non-standard' conditions, particularly weather and other causes such as the wear of the guns and altitude differences between guns and targets.  For this reason the British generally used a 'planning range' at about 90% of range table maximum range.  In addition indirect fire artillery is usually deployed some distance behind the 'front line', so that it is not directly visible to the enemy.  Obviously this distance depends on the terrain, but roughly 1/3 of maximum range would be a reasonable rule of thumb for distance behind the front.  Furthermore firing near maximum range is less accurate, less consistent and causes more barrel wear than shorter ranges with smaller propelling charges, and sometimes requires special cartridges 'Charge Super'.  

Arc of fire is also a factor in concentrating the fire of many batteries.  Guns have top traverse, the amount the saddle can move left and right on the carriage or mounting.  However the gun itself can also be moved to cover a wider arc.  The ease and speed of this is dependant on the weight of the gun.  Of course the arc of fire may be limited by the terrain and topography around the gun position.

Making comparisons between 'text book' ranges can be slightly misleading because these ranges are based on 'standard conditions', and different armies used different 'standard conditions' in World War 2 (WW2).  For example, in WW2 the range table maximum range for a 25-pdr was 13,400 yards.  In the 1950's UK adopted new NATO (actually ICAO) standard conditions, whereupon the 25-pdr maximum range became 13,600 yards!  Another national variable is the criterion used to select the standard Muzzle Velocity (MV), a gun's MV rises with initial use then falls as the gun wears.  Traditionally the French used the peak MV, accentuating the 'maximum range', others use the new gun MV and UK generally used one for a worn barrel past its peak.  

For a given elevation angle the main determinant of range is MV (higher means more range), and MV can be increased either by using more propellant or a lighter shell for the same amount of propellant, mediated by the shell's shape (ballistic efficiency). That said, for a given MV and elevation a heavier shell will go further than a lighter one, although it needs more propellant to get that MV.

The following table shows many of the most widely used guns of WW2, UK used those in blue, for more details see 'Guns'.  None have been adjusted to standardise standard conditions or the point in a gun's life for the standard MV, therefore their precise maximum ranges do not give the precisely true relative picture.  Of course in the end this standardisation would be fairly meaningless in practical terms because the wind component of weather conditions may favour one side of opposing artilleries and so disadvantage the other, and guns will all be at different stages of wear.  Disparities between MV, shell weight and resultant range reflect the shell's shape - ballistic efficiency.




Shell Weight



Gun Weight

Top Traverse

7.5-cm Gun M95


75 mm

6.5 kg

500 m/s

10,950 m

1,105 kg

25° L & R

75-mm How M8


75 mm

6.3 kg

595 m/s

8,500 m

610 kg

30° L & R

76-mm M42


76.2 mm

6.3 kg

680 m/s

11,156 m

1,115 kg

27° L & R

3.7-inch How


94 mm

9.1 kg

295 m/s

5,486 m

840 kg

20° L & R

25-pdr Gun


88 mm

11.3 kg

520 m/s

12,253 m

1,825 kg

4° L & R + platform
SP Sexton 24°L, 16°R

105-mm How M2A1


105 mm

15.0 kg

470 m/s

11,200 m

2,260 kg

23° L & R
SP M7 15°L, 30°R

10.5-cm le FH18


105 mm

14.8 kg

470 m/s

10,675 m

1,985 kg

28° L & R

10.5-cm le FH18M


105 mm

14.8 kg

540 m/s

12,325 m

2,040 kg

28° L & R

10.5-cm How M91


105 mm

15.8 kg

545 m/s

10,765 m

1,495 kg

20° L & R

122-mm How M38


122 mm

21.8 kg

500 m/s

11,800 m

2,450 kg

25° L & R

122-mm Gun M31/37


122 mm

25 kg

800 m/s

20,400 m

7,250 kg

28° L & R

4.5-inch Gun


114 mm

 24.9 kg

685 m/s

18,290 m

 5,735 kg

30° L & R

5.5-inch Gun (80 lb/100 lb shells)


140 mm

37.2/45.6 kg

595/510 m/s

16,400/14,860 m

5,784 kg

30° L & R

15-cm sFH18


150 mm

43.5 kg

495 m/s

13,250 m

6,500 kg

32° L & R

15-cm K18


150 mm

43.0 kg

890 m/s

24,500 m

12,760 kg

10° L & R + platform

150-mm How Type 96


150 mm

30.8 kg

805 m/s

11,870 m

4,135 kg

15° L & R

152-mm How M1943


152 mm

39.9 kg

510 m/s

12,400 m

3,600 kg

35° L & R

152-mm Gun How M1937


152 mm

43.6 kg

655 m/s

17,265 m

7,130 kg

28° L & R

155-mm How M1


155 mm

44.1 kg

565 m/s

15,000 m

5,765 kg

26.5° L & R

155-mm Gun M1


155 mm

44.1 kg

853 m/s

23,500 m

13,880 kg

30° L & R

17-cm K18


170 mm

68.0 kg

925 m/s

29,600 m

17,520 kg

16° L & R  + platform

7.2-inch How MkVI


183 mm

91.6 kg

586 m/s

17,995 m

13,220 kg

30° L & R

8-inch How M1


203 mm

90.7 kg

595 m/s

16,970 m

14,427 kg

30° L & R

203-mm How M1931


203 mm

100 kg

607 m/s

18,025 m

17,700 kg

4° L & R

8-inch Gun M1


203 mm

109.1 kg

865 m/s

32,015 m

31,460 kg

15° L & R

240-mm How M1


240 mm

163.3 kg

700 m/s

15,045 m

28,449 kg

22.5° L & R

If guns can't quickly and easily traverse between widely separated targets then they are restricted in using their range laterally, even if the control arrangements enabled them to fire across unit and formation boundaries.  In WW2 most heavy and self-propelled guns were limited in this way.   Most guns have a traverse capability in two forms: top traverse and carriage traverse.  The former is effected via the handwheel that rotates the saddle (carrying the barrel, etc) on a pivot fixed to the carriage.  The latter means physically moving the carriage while keeping the dial sight in the same place.  This was normally fairly easy for field guns such as 105-mm M2 (it's not too heavy) and extremely easy with 25-pdr because of its platform - one man could do it.  It was physically harder with 5 or 6 tons of medium gun such as 5.5-inch needing men lifting each trail and others pushing.  However, it was generally impractical with guns such as 155-mm Gun M1 unless there was plenty of time because the gun had to be brought out of action, moved, new forward spade pits dug, and then brought back into action taking perhaps 45 minutes or so (and a lot of sweat).  SP guns also had to be brought out of action because of the difficult in keeping their dial sight in the right place when moving the carriage, although this could be done quite quickly.  An added constraint on traverse could be the local terrain, for example if guns were close to buildings or trees, or if the guns were in gun-pits that permitted only  limited traverse.

The following chart translates angular arcs in degrees into widths in yards at different ranges, although labeled in yards it can be equally read in metres.  It perhaps explains the popularity of 60° arc (ie 30° left and right), the width of the arc is the same as the range.  Of course the actual total width of arc cannot be more than twice a gun's maximum range!

Arcs ranges and  coverage

The final but first question about the artillery system is 'what is artillery fire trying to achieve'.  Many, if not most people, would probably say 'kill and destroy the enemy', perhaps adding 'casualties and damage'.  These are undoubtedly desirable effects in most circumstances.  However, by the middle of World War 1 the British and Germans had realised that this was not the complete story, bombarding the enemy to destroy them before an attack did not work.  The British and Germans (the latter in the person of Colonel Georg Bruckmüller) realised that neutralisation was the key to success.  In essence neutralisation meant that the enemy was prevented from doing what they should be doing, it negated their effectiveness.  The critical circumstance was during the attack, effective neutralising fire forced the enemy to 'keep their heads down' and so left the assaulting troops unmolested.  The practical problem was that neutralisation and its essential integration with the infantry or armoured assault was difficult - timing was crucial so that the attackers arrived on the enemy position as soon as possible after artillery fire lifted, 2 minutes at most.  This was the difficult and dangerous bit.



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