Artillery - Field Artillery System

Field Artillery System

Because field artillery mostly uses indirect fire the guns have to be part of a system that enables them to attack targets invisible to them in accordance with the combined arms plan.

The main functions in the field artillery system are:

• Communications
• Command: authority to allocate resources;
• Target acquisition: detect, identify and deduce the location of targets;
• Control: authority to decide which targets to attack and allot fire units to the attack;
• Production of firing data – to deliver fire from a fire unit onto its target;
• Fire units: guns, launchers or mortars grouped together;
• Specialist services – produce data to support the production of accurate firing data;
• Logistic services – to provide combat supplies, particularly ammunition, and equipment support.

Organisationally and spatially these functions can be arranged in many ways. Since the creation of modern indirect fire different armies have done it differently at different times and in different places. Technology is often a factor but so are military-social issues, the relationships between artillery and other arms, and the criteria by which military capability, efficiency and effectiveness are judged. Cost is also an issue because artillery is expensive due to the large quantities of ammunition that it uses and its level of manpower.

Communications underpin the artillery system, they have to be reliable and in real-time to link the various elements. During the 20th century communications used flags, morse code by radio, line and lights, voice and teleprinter by line. Radio has included HF, VHF, satellite and radio relay as well as modern tactical trunk systems. In western armies at least radio communications are now usually encrypted.

The emergence of mobile and man-portable radios after World War I had a major impact on artillery because it enable fast and mobile operations with observers accompanying the infantry or armoured troops. In World War II some armies fitted their self-propelled guns with radios. However, sometimes in the first half of the 20th century hardcopy artillery fire plans and map traces were distributed.

Data communications can be especially important for artillery because by using structured messages and defined data types fire control messages can be automatically routed and processed by computers. For example a target acquisition element can send a message with target details which is automatically routed through the tactical and technical fire control elements to deliver firing data to the gun's laying system and the gun automatically laid. As tactical data networks become pervasive they will provide any connected soldier with a means for reporting target information and requesting artillery fire.

Command is the authority to allocate resources, typically by assigning artillery formations or units. Terminology and its implications vary widely. However, very broadly, artillery units are assigned in direct support or in general support. Typically, the former mostly provide close support to manoeuvre units while the latter may provide close support and or depth fire, notably counter-battery. Generally, 'direct support' also means that the artillery unit provides artillery observation and liaison teams to the supported units. Sometimes direct support units are placed under command of the regiment/brigade they support. General support units may be grouped into artillery formations for example, brigades even divisions, or multi-battalion regiments, and usually under command of division, corps or higher HQs. General support units tend to be moved to where they are most required at any particular time. Artillery command may impose priorities and constraints to support their combined arms commander's plans.

Target acquisition can take many forms, it is usually observation in real time but may be the product of analysis. Artillery observation teams are the most common means of target acquisition. However, air observers have been use since the beginning of indirect fire and were quickly joined by air photography. Target acquisition may also be by anyone that can get the information into the artillery system. Targets may be visible to forward troops or in depth and invisible to them.

Observation equipment can vary widely in its complexity.

• Unmanned air vehicles are the latest form of air observation, having been first introduced in the early 1960s.
• The equipment available to observation teams has progressed from just prismatic compass, hand-held or tripod mounted binoculars and sometimes optical range-finders.
• Special equipment for locating hostile artillery: flash spotting and notably sound ranging appeared in World War I the latter has been undergone increasing refinement as technology has improved. These were joined by radar in World War II.
• In the mid-1970s several armies started equipping their artillery observation teams with laser rangefinders, ground surveillance radars and night vision devices, these were soon followed by inertial orienting and navigating devices to improve the accuracy of target locations. The Global Positioning System (GPS) provided a smaller and cheaper means of quick and accurate fixation for target acquisition devices.
• Specialised units with ground surveillance radars, unattended ground sensors or observation patrols operating in depth have also been used.
• Targets in depth may also be 'acquired' by intelligence processes using various sources and agencies such as HUMINT, SIGINT, ELINT and IMINT.
• Laser guided shells require laser target designators, usually with observation teams on the ground but UAV installations are possible.
• Specialised artillery observation vehicles appeared in World War II and have greatly increased in sophistication since that time.

Control, sometimes called tactical fire control, is primarily concerned with 'targeting' and the allotment of fire units to targets. This is vital when a target is within range of many fire units and the number of fire units needed depends on the nature of the target, and the circumstances and purpose of its engagement. Targeting is concerned with selecting the right weapons in the right quantities to achieve the required effects on the target. Allotment attempts to address the artillery dilemma—important targets are rarely urgent and urgent targets are rarely important. Of course importance is a matter of perspective; what is important to a divisional commander is rarely the same as what is important to an infantry platoon commander.

Broadly, there are two situations: fire against opportunity targets and targets whose engagement is planned as part of a particular operation. In the latter situation command assigns fire units to the operation and an overall artillery fire planner makes a plan, possibly delegating resources for some parts of it to other planners. Fire plans may also involve use of non-artillery assets such as mortars and aircraft.

Control of fire against opportunity targets is an important differentiator between different types of artillery system. In some armies only designated artillery HQs have the tactical fire control authority to order fire units to engage a target, all 'calls for fire' being requests to these HQs. This authority may also extend to deciding the type and quantity of ammunition to be used. In other armies an 'authorised observer' (for example, artillery observation team or other target acquisition element) can order fire units to engage. In the latter case a battery observation team can order fire to their own battery and may be authorised to order fire to their own battalion and sometimes to many battalions. For example a divisional artillery commander may authorise selected observers to order fire to the entire divisional artillery. When observers or cells are not authorised they can still request fire.

Armies that apply forward tactical control generally put the majority of the more senior officers of artillery units forward in command observation posts or with the supported arm. Those that do not use this approach tend to put these officers close to the guns. In either case the observation element usually controls fire in detail against the target, such as adjusting it onto the target, moving it and co-ordinating it with the supported arm as necessary to achieve the required effects.

Firing data has to be calculated and is the key to indirect fire, the arrangements for this have varied widely. In the end firing data has two components: quadrant elevation and azimuth, to these may be added the size of propelling charge and the fuze setting. The process to produce firing data this is sometimes called technical fire control. Before computers, some armies set the range on the gun's sights, which mechanically corrected it for the gun's muzzle velocity. For the first few decades of indirect fire, the firing data were often calculated by the observer who then adjusted the fall of shot onto the target.

However, the need to engage targets at night, in depth or hit the target with the first rounds quickly led to predicted fire being developed in World War I. Predicted fire existed alongside the older method. After World War II predicted methods were invariably applied but the fall of shot usually needed adjustment because of inaccuracy in locating the target, the proximity of friendly troops or the need to engage a moving target. Target location errors were significantly reduced once laser rangefinders, orientation and navigation devices were issued to observation parties.

In predicted fire the basic geospatial data of range, angle of sight and azimuth between a fire unit and its target was produced and corrected for variations from the 'standard conditions'. These variations included barrel wear, propellant temperature, different projectiles weights that all affected the muzzle velocity, and air temperature, density, wind speed & direction and rotation of the earth that affect the shell in flight. The net effect of variations can also be determined by shooting at an accurately known point, a process called 'registration'.

All these calculations to produce a quadrant elevation (or range) and azimuth were done manually by highly trained soldiers using instruments, tabulated data, data of the moment and approximations until battlefield computers started appearing in the 1960s and 1970s. While some early calculators copied the manual method (typically substituting polynomials for tabulated data), computers use a different approach. They simulate a shell's trajectory by 'flying' it in short steps and applying data about the conditions affecting the trajectory at each step. This simulation is repeated until it produces a quadrant elevation and azimuth that lands the shell within the required 'closing' distance of the target co-ordinates. NATO has a standard ballistic model for computer calculations and has expanded the scope of this into the NATO Armaments Ballistic Kernel (NABK) within the SG2 Shareable (Fire Control) Software Suite (S4).

Technical fire control has been performed in various places, but mostly in firing batteries. However, in the 1930s the French moved it to battalion level and combined it with some tactical fire control. This was copied by the US. Nevertheless most armies seemed to have retained it within firing batteries and some duplicated the technical fire control teams in a battery to give operational resilience and tactical flexibility. Computers reduced the number of men needed and enabled decentralisation of technical fire control to autonomous sub-battery fire units such as platoons, troops or sections, although some armies had sometimes done this with their manual methods. Computation on the gun or launcher, integrated with their laying system, is also possible. MLRS led the way in this.

A fire unit is the smallest artillery or mortar element, consisting of one or more weapon systems, capable of being employed to execute a fire assigned by a tactical fire controller. Generally it is a battery, but sub-divided batteries are quite common, and in some armies very common. On occasions a battery of 6 guns has been 6 fire units. Fire units may or may not occupy separate positions. Geographically dispersed fire units may or may not have an integral capability for technical fire control.

Specialist services provide data need for predicted fire. Increasingly, they are provided from within firing units. These services include:

• Survey: accurate fixation and orientation of the guns, historically this involved specialists within field artillery units and specialist units. In some armies mapping and amp supply has also been an artillery responsibility. Survey is also essential for some target acquisition devices. Traditional survey methods of measurement and calculation have been replaced by inertial orientation and navigators and GPS.
• Meteorological data: historically these were usually divisional level specialist teams but advances in technology mean they are now increasingly part of artillery units.
• Calibration: periodically establishing the "normal" muzzle velocity of each gun as it wears. Originally this involved special facilities and army level teams. Measurement using Doppler radar, introduced in the 1950s, started to simplify arrangements. Some armies now have a muzzle velocity measuring radar permanently fitted to every gun.

Logistic services, supply of artillery ammunition has always been a major component of military logistics. Up until World War I some armies made artillery responsible for all forward ammunition supply because the load of small arms ammunition was trivial compared to artillery. Different armies use different approaches to ammunition supply, which can vary with the nature of operations. Differences include where the logistic service transfers artillery ammunition to artillery, the amount of ammunition carried in units and extent to which stocks are held at unit or battery level. A key difference is whether supply is 'push' or 'pull'. In the former the 'pipeline' keeps pushing ammunition into formations or units at a defined rate. In the latter units fire as tactically necessary and replenish to maintain or reach their authorised holding (which can vary), so the logistic system has to be able to cope with surge and slack.

Artillery has always been equipment intensive and for centuries artillery provided its own artificers to maintain and repair their equipment. Most armies now place these services in specialist branches with specialist repair elements in batteries and units.