Field artillery

Field artillery is a category of mobile artillery weapon used to support armies in the field. These weapons are specialized for mobility and tactical efficiency, and not for long range nor sheer destructive power.

Types

infantry support guns - directly support infantry units (mostly obsolete)
mountain guns - lightweight weapons that can be moved through difficult terrain
field guns - capable of long range fire
howitzers - capable of high angle fire
gun howitzers - capable of high or low angle fire with a long barrel
mortars - lightweight weapons that fire projectiles at an angle of over 45 degrees to the horizontal

The revolution in artillery capabilities and range

Prior to the first World War, field artillery batteries generally fired directly at visible targets measured in distances of meters and yards. Today, modern field batteries measure targets in kilometers and miles and no longer directly engage the enemy with observed direct fire. This hundred-fold increase in the range of artillery guns in the 20th century has been the result of development of rifled cannons, improvements in propellants, better communications between observer and gunner and technical improvements in gunnery computational abilities.

Most field artillery situations require indirect fire due to weather, terrain, night-time conditions, distance or other obstacles. These gunners can also rely upon a trained artillery observer, also called a forward observer who sees the target, relays the coordinates of the target to their fire direction center which, in turn translates those coordinates into: a left-right aiming direction; an elevation angle; a calculated number of bags of propellant and finally a fuze with a determined waiting time before exploding, (if necessary) to be set, which is then mated to the artillery projectile now ready to be fired.

Field artillery team

Modern field artillery (Post-World War I) has three distinct parts: the forward observer (or FO), the fire direction center (FDC) and the actual guns themselves. On the battlefield, there will be combinations of all of the following elements.

FO (Forward Observer)

Because artillery is an indirect fire weapon, the forward observer must take up a position where he can observe the target using tools such as binoculars and laser range-finders and designators and call back fire missions on his radio. This position can be anywhere from a few thousand meters to 20-30 km distant from the guns.

Using a standardized format, the FO sends either an exact target location or the position relative to his own location or a common map point, a brief target description, a recommended munition to use, and any special instructions such as "danger close" (the warning that friendly troops are within 600 metres of the target, requiring extra precision from the guns). Once firing begins, if the rounds are not accurate the FO will issue instructions to adjust fire and then call "fire for effect."

The FO does not talk to the guns directly - he deals solely with the FDC except in the case of CAS (Close Air Support). The forward observer can also be airborne and in fact one of the original roles of aircraft in the military was airborne artillery spotting.

The FO may be called upon to direct fire for CAS and/or Naval GunFire in addition to Field Artillery based howitzer and Infantry based mortar units.

The US Army Field Manual describing the duties and responsibilities is FM 6-30, Tactics, Techniques, and Procedures for Observed Fire.

File:785px-Arty Call for Fire 1.jpg

Calling in and adjusting artillery fire on a target visible to a forward observer but not to the soldiers manning the guns, themselves

"HALO HALO ARTILLERY QUEEN OF BATTLE FOLLOW ME"

FDC (Fire Direction Center)

Typically, there is one FDC for a battery of six guns, in a light division. In a typical heavy division configuration, there exist two FDC elements capable of operating two four gun sections, also known as a split battery. The FDC computes firing data, fire direction, for the guns. The process consists of determining the precise target location based on the observer's location if needed, then computing range and direction to the target from the guns' location. These data can be computed manually, using special protractors and slide rules with precomputed firing data. Corrections can be added for conditions such as a difference between target and howitzer altitudes, propellant temperature, atmospheric conditions, and even the curvature and rotation of the Earth. In most cases, some corrections are omitted, sacrificing accuracy for speed. In recent decades, FDCs have become computerized, allowing for much faster and more accurate computation of firing data.

CP

In the Irish Army the Command Position or CP is in control of an artillery battery. It is usually located at battery centre. The CP should be well camouflaged, but the CPO (Command Position Officer) should be able to see all the guns with ease. Gun markers are placed in front of the CP to remind the CPO which gun is in which position. The CPO is assisted by two "Acks" who operate the fire data computers called gunzens. The GPO (Gun Position Officer) and CPO work at the plotter to ensure that the data calculated by the Acks is accurate and safe. The CP signaller is contact with the OP, or Observation Post, where the FOO, or Forward Observer Officer, works with the OP team to identify targets and call-back fire data. In recent years, headset radios have become common for communication between the CPO and gun detachment commanders.

Guns

The final piece of the puzzle is the "gun line" itself. The FDC will transmit a warning order to the guns, followed by orders specifying the type of ammunition and fuze setting, bearing, elevation, and the method of adjustment or orders for fire for effect (FFE). Elevation (vertical direction) and bearing orders are specified in milliradians) or mils, and any special instructions, such as to wait for the observer's command to fire relayed through the FDC. The crews load the howitzers and traverse and elevate the tube to the required point, using either hand cranks (usually on towed guns) or hydraulics (on self-propelled models).

Parent battalion and US Army brigade/USMC regimental FDCs

FDCs also exist in the next higher parent battalion that "owns" 2-4 artillery batteries. Once again, an FDC exists at the US Army brigade or USMC regimetal level that "owns" the battalions. These higher level FDCs monitor the fire missions of their subordinate units and will coordinate the use of multiple batteries or even multiple battalions in what is called a battalion or brigade/regimental mission. In training and wartime execises, as many as 72 guns from 3 battalions may all be coordinated to put "steel on the target" in what is called a "brigade/regimental time on target" or brigade/regimental TOT for short. The rule is "silence is consent," meaning that if the lower unit does not hear a "cancel the mission" (don't shoot) or even a "check firing" (cease firing) order from the higher monitoring unit, then the mission goes on. Higher level units monitor their subordinate unit's missions both for active as well as passive purposes. Higher level units also may get involved to coordinate artillery fire across fire support coordination boundaries (often parallel lines on maps) where one unit can not fire into without permission from higher and/or adjacent units that "own" the territory.