Field artillery

This article describes field artillery in general. See Field Artillery for the U.S. field artillery. Also see artillery

Field artillery is a category of mobile weapons used to support armies in the field. This article concerns these categories only:

• mountain guns - lightweight weapons that can be moved through difficult terrain.
• howitzers - capable of high angle fire.
• gun-howitzers - capable of high or low angle fire with a long barrel.
• self-propelled artillery - with guns or gun howitzers mounted on a vehicle.

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.

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. The forward observer can also be airborne and in fact one of the original roles of aircraft in the military was airborne artillery spotting.

Typically, there is one FDC for a battery of six guns. 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, drift of the projectile due to the right-hand spin imparted by the howitzer's rifling, 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.

The final piece of the puzzle is the "gun line" itself. The FDC will transmit the fire order to the guns, specifying the number of volleys, a particular shell and fuze combination, the specific charge, a deflection (horizontal direction) and quadrant elevation (vertical direction) both specified in 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).