Field artillery
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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.
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[edit] 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
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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).
[edit] 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.
